Final Flashcards
What is immunology?
Study of hosts reactions to foreign substances that are introduced into the body
What is an antigen?
A substance that reacts with an antibodies or sensitized cells but may or may not be able to elicit an immune response
What is immunity?
Condition of being resistant to infection
Who is the father of immunology?
- Louise Pasteur
- he created the first attenuated vaccine
What is attenuation?
- makes pathogens
- takes place through heat, aging and chemicals
What is phagocytosis?
Cells that eat cells
What is humoral immunity?
- Protection from disease resulting from substances in the serum/plasma (antibodies and acute phase reactants)
What are the two types of the adaptive immune response?
- cellular
- humoral
What is the function of humoral immunity?
Involves production of antibodies by B cells and plasma cells
What are antibodies?
- serum proteins used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses
What is innate immunity?
An individual ability to resist infection by means of normally present body functions
What are characteristics of the innate immunity?
- nonspecific
- no memory
- immediate exposure
- same response for all pathogens
- influenced by nutrition, age, fatigue, stress, and genetic determinants
What is adaptive immunity?
Resistance that is characterized by specificity for each individuals pathogen
What are characteristics of adaptive immunity?
- delayed response
- stronger response
- specific
- has memory
What is the function of WBCs?
Defend against invasion by bacteria, virus, fungi, and other foreign substances
What are the 5 types of leukocytes?
- monocytes
- lymphocytes
- basophil
- eosinophil
- neutrophils
What WBC is part of the adaptive immunity?
Lymphocytes
What are the main cells found in tissues?
- dendritic cells
- macrophages
- mast cells
What are hematopoietic stem cells (HSC)?
All blood cell types arise from this cell
Where are WBC produced? How much?
- bone marrow
- one and a half billion daily
What two distinct types of precursors does HSC give rise to?
- common myeloid precursors (CMP)
- common lymphoid precursors (CLP)
What do CMPs do?
- give rise to WBC that participate in phagocytosis
- also known as myeloid line
What are characteristics of Neutrophils?
- life span in several days
- nucleus has 2-5 lobes (has lots of granules)
- 50-70% of WBC
- use wright stain
What is the main function of neutrophils?
Phagocytosis
What is diapedesis?
Movement through blood vessel wall
What are chemotaxins?
Chemical messengers that cause cells to migrate in particular direction
What are characteristics of eosinophils?
- 1-4% of WBC
- eosin stain
- bilobed/eccentrically located nucleus
What are the functions of eosinophils?
1) phagocytosis (not as efficient as neutrophils)
2) neutralize basophils and mast cells
3) kills parasites using cationic proteins
4) MOST IMPORTANT: regulation of adaptive immune response through cytokine release
What are characteristics of basophils?
- less than 1% of WBC
- smallest
- nucleus is bilobed, and has deep purple-blue granules (hard to see)
- life span is a few hours
What happens to basophils in the spleen?
Removed and destroyed by marcrophages
What are the 3 main functions of basophils?
1) induce and maintain allergic reactions
2) regulate some Th cell response
3) stimulate B-cells to produce IgE antibody
What is the function of histamine?
Contracts smooth muscle
What is the function of heparin?
Anticoagulant
What are characteristics of monocytes?
- Largest
- irregular horseshoe or folded nucleus (occupies half or more of cell)
- 2-10% of WBC
- 30 hour lifespan
- after 30 hours, travels to tissue and becomes macrophage
Why are neutrophils more efficient at phagocytosis than macrophages?
Macrophages are slower
Why are neutrophils more efficient at phagocytosis than eosinophils?
- less eosinophils
- eosinophils lack digestive enzymes
What is the lifespan of macrophages?
A few months
What are the functions of innate immunity?
1) phagocytosis
2) microbial killing
3) anti-tumor activity
4) intracellular parasite eradication
5) secretion of cell membrane
How do macrophages play an important role in the adaptive system?
By presenting phagocytosized antigens to T cells
Where are mast cells found?
- located in variety of tissues (resembles a basophil)
What are the functions of mast cells?
1)act to increase vascular permeability and increase blood flow to affected area
2) role in allergic reactions
3) APC
Describe the appearance of dendritic cells
Covered with long membraneous extensions that resemble nerve cell dendrites
What are dendritic cells?
- APC that links innate and adaptive immunity and are critical for the induction of immune response
- classified according to location
What is the most potent phagocytic cell?
Dendritic cells
What are characteristics of lymphocytes?
- 20-40% of WBC
- large, rounded and indented nucleus
- similar size to RBC
- has narrow ring
- chromatin stains deep blue
- sparse cytoplasm
Why are lymphocyte granules unique?
They arise from HSC
What are the 3 types of lymphocytes?
- T cells
- B cells
- innate lymphoid cells
What is the most prominent innate lymphoid cells?
NK cells
What % of lymphocytes are B cells?
10-20%
What % of lymphocytes are T cells?
61-80%
What % of lymphocytes are NK cells?
10-15%
What is cluster of differentiation?
Protein found of cells surfaces that can be used to identify specific cell types and stages of differentiation
What are the primary lymphoid organs
Bone marrow
Thymus
What is the largest tissue in the body?
Bone marrow
What is bone marrow the main source of?
HSC
What can HSC develop into?
- RBCs
- lymphocytes
- monocytes
- granulocytes
- platelets
What occurs when lymphocytes remain in the bone marrow?
Mature and become NK cells or B cells
What occurs when the lymphocytes travel to the thymus?
Mature and become T cells
Describe the thymus
Filled with epithelial cells that play central role in differentiation process
How long does it take T cells to mature?
3 weeks
What are mature T cells released from?
Medulla thymus
What are the secondary lymphoid organs?
- spleen
- lymph nodes
- CALT
- MALT
Where does main contact of foreign antigens occur?
- secondary lymphoid organs
- T cells and B cells meet here as well
Where do lymphocytes spend most of their time?
The tissues
How do lymphocytes travel to blood stream?
Via. Thoracic duct
What is the largest lymphatic vessel?
Thoracic duct
What is lymphopoiesis?
Multiplication of lymphocytes
Where is the spleen located?
- upper left quadrant
- below diaphragm
- largest secondary organ
What is the function of the spleen?
Removes old/damaged cells and foreign antigens from the blood
What is the function of red pulp?
- to destroy old RBCs, platelets, and pathogens
What is rich in red pulp?
Macrophages
What is % of red pulp found in the spleen?
50%
What % of white pulp is found in the spleen?
20%
What is the main function of lymph nodes?
- Filtration of interstitial fluid from around cells in tissues
- important because it allows contact between lymphocytes and foreign antigens that have penetrated tissue
What are the layers of lymph node tissues?
- outer cortex
- para cortex
- inner medulla
What is lymph fluid?
A filtrate of blood and arises from the passage of water and low molecular weight solutes out of blood vessels walls and into the interstitial spaces between cells
What cells could be found in a primary follicle of the lymph nodes?
- stimulated B cells
- macrophages
- follicular dendritic
What cells can be found in a secondary follicle of lymph nodes?
Antigen stimulated proliferating B cells
What is at the center of a secondary follicle of the lymph nodes called?
Germinal center
What happens when B cells come in contact with antigens?
Plasma cells and memory cells form
Where can T cells be found in the lymph nodes?
Paracortex
What is the main function of plasma cells?
Actively secrete antibodies
What is the main function of memory cells?
Can quickly change into plasma cells
Where can MALT be found?
- appendix
- GI tract
- ileum
- peyers patch
- respiratory tract
- tonsils
- urogenital tract
Why are macrophages and lymphocytes and localized in MALT?
Mucosal surface are main ports of entry for a foreign antigen
What cells cab be found in CALT?
- dendritic cells
- macrophages
- monocytes
What are innate phagocytic cells?
- dendritic cells
- macrophages
- monocytes
- neutrophils
Describe NK cells
- can kill virally infected or cancerous target cells without previous exposure to them
- first line of defense against virally infected cells
- no specificity
- enhanced by exposure to cytokines: IL-12, INF-alpha, and INF-beta
How are T cells different from NK cells?
- only NK cells are able to kill target cells without prior exposure to them
What is the most potent phagocytic cell?
Dendritic cells
What is the main function of T-cells?
- produce cytokines that regulate both innate and adaptive immunity
What blood cell kills parasite?
Eosinophils
What are the 2 systems of the innate immunity?
- external defense system
- internal defense system
Describe the external defense system of innate immunity
- contains chemical, physical, and biological factors that work together to prevent most infections agents from entering the body
Describe the internal defense system of the innate immunity
- triggered within minutes and clears invaders as quickly as possible
Describe the outer layer of the external defense barrier
- outer layer of skin is the epidermis and contains several layers of tightly packed epithelial cells
- proteins coated cell called keratin
What is the role of keratin in the epidermis?
Makes skin impermeable to most infectious agents
What is the layer under the epidermis?
Dermis
Describe dermis
- thicker than epidermis
- connective tissue with blood vessels, hair follicles, sebaceous glands, and WBC
What cells are found in the dermis?
- dendritic cells
- macrophages
- mast cells
Why does skin have several secretions?
Discourage growth of microorganisms
What is secreted on the skin to maintain pH balance? What is the pH?
- fatty acids and lactic acid
- they prevent growth of microorganisms
- ~5.6
what is psoriasis?
- produced by skin
- has antibacterial effects, especially for gram negative bacteria
What is the respiratory tracts external defense system?
- mucous secretion block adherence
- coughing and sneezing clear out pathogens
What is the genitourinary tracts external defense systems?
- flushing out urine
- acidity helps to remove many potential pathogens
- lactic acid of vagina maintains pH of 5
What is the external defense for the digestive tract?
-hydrochloric acid keeps pH as low as 1 to kill pathogens brought in by food and drink
What are the lysosomes role in the external defense system?
- attack cell wall of microorganisms, especially gram positive bacteria
What is microbiota?
A mix of bacteria that are normally found at species body sites and do not typically cause disease
Explain the internal defense system of innate immunity
- composed of both cells
- soluble factors that have specific and essential functions
What is the function of phagocytes?
- they engulf and destroy most foreign cells or particles that enter the body
What is the % of dendritic cells and macrophages found in tissues?
10-15%
What are the most important cells in pathogen recognition?
- dendritic cells
- macrophages
What is the main function of patter recognition receptors (PRRs)?
- able to distinguish pathogens from normally present molecules in the body by means of receptors
What happens when PRRs binds to pathogen?
1) phagocytic cells activate and are better able to engulf and kill organisms
2) activated cells secrete proinflammatory cytokines and chemokines
3) cytokines and chemokines also trigger adaptive immune response
Describe pathogen associated molecular patterns (PAMPs)?
Substances that allows PRRs to have ability to distinguish self from non-self
What TLRs are found in cytoplasm?
- TLR1
- TLR2
- TLR4
- TLR5
- TLR6
What TLRs are found in the endosomal compartment of cells?
- TLR3
- TLR7
- TLR8
- TLR9
What are c-lectin receptors (CLRs)?
- plasma membrane receptors that bind to Mannan and beta-glucans found in fungal cell walls
Describe serum amyloid A
- major protein who concentration can increase X1000 in response to infection/injury
- apolipoprotein synthesized in liver
- acts like cytokines, chemical messenger (activates monocytes and macrophages
Why would serum amyloid A be increased?
- chronic inflammation
- atherosclerosis
- cancer
Describe complement
- series of serum proteins that are normally present and contribute to inflammation
What are the functions of complement?
1) opsonization
2) chemotaxis
3) lysis of cells
What is elastase?
- an enzyme secreted by neutrophils during inflammation that can degrade elastin and collagen
What are the pro inflammatory cytokines?
- TNF- alpha
- interleukin-1beta
- interleukin-6
Describe haptoglobin
- alpha1-globulin
- binds irreversibly to free hemoglobin
- acts as antioxidant to protect against oxidative damage from free hemoglobin
Describe fibrinogen
- acute phase protein involved in coagulation pathway
- small portion cleaned by thrombin to form fibrils that create a fibrils clot
What do fibrin clots do?
- increases strength with wound and stimulate endothelial cell adhesion and proliferation
- creates barrier of microorganisms further into the body
Describe ceruloplasmin
- consists of a single polypeptide chain
- copper transporting protein in human plasma
- acts as enzyme, converting the toxic ferrous ion (Fe^2+) to non toxic ferric form ( Fe^3+)
What disease is characterized by depletion of ceruloplasmin?
Wilsons disease
What is inflammation?
Body’s overall reaction to injury or invasion by an infectious agent
What are the 4 cardinal signs of inflammation?
- erythema (redness)
- edema (swelling)
- heat
- pain
What is the acute inflammatory response?
- acts it combat the early stages of infection and also begins a process that repairs tissues damage
What cells are most active in phagocytosis?
- dendritic cells
- macrophages
- monocytes
- neutrophils
What are selectins?
- adhesion molecules on endothelial cells lining blood vessels
what are integrins?
- adhesion molecules on endothelial cell wall
What is chemotaxis?
- cells are attracted to site of inflammation by chemical substances such as soluble bacteria factors and acute phase reactants
What enhances the binding process during phagocytosis?
Opsonins
what are opsonins?
Serum proteins that attach to a foreign cell or pathogen and make it more susceptible to phagocytosis
What are phagosomes?
Pseudopodia fuse to completely enclose pathogen
What are phagolysosome?
Lysosomal granule fused to phagosome
What are the two processes that eliminate pathogens?
- oxygen-dependent pathway
- oxygen-independent pathway
Describe oxygen-dependent pathway
- increase in oxygen consumption (oxidative burst) occurs in cell as the pseudopodia enclose particles within vacuole
- generates considerable energy through oxidative metabolism
What is an important bacterial agent in oxygen dependent process?
Hydrogen peroxide
Describe oxygen-independent pathway
- defensins kill gram-negative bacteria, many fungi, and some viruses
What are defensins?
Small cationic proteins that cleave segments without benefits of oxygen
What is cytotoxicity?
- the degree to which a substance can cause damage to a cell
What are two main binding receptors for NK cells?
1) inhibitory receptors
2) activating receptors
What do inhibitory receptors do?
Deliver inhibitor signals
What do activating receptors do?
Delivers signals to activate cytotoxic mechanism
What are perforins?
Proteins that form channels in target cells
What are granzymes?
Packets of enzymes tat may enter through channels and mediate cell lysis
Describe antibody-dependent cellular cytotxocity
- NK cells recognize and lysis antibody-coated target cells
- binding occurs through surface receptors; CD16 and CD32, which bind to Fc portion of immunoglobulins
- destruction occurs outside of NK cells
- important contributor to anti-tumor activity
Describe innate lymphoid cells
- growing family of immune cells that develop from the common lymphoid progenitor but does not express markers of lymphocytes lineage
- primarily found in mucosal sites
What can measurements of CRP levels be used for?
- tracking progress of organ transplant
- monitoring drug therapy with anti-inflammatory agents
- determining active phases of RA
What are the functions of C-reactive protein?
1) opsonization
2) complement activation
What is the function of serum amyloid A?
Activates monocytes and macrophages
What is the function of alpha1-antitrypsin?
Proteases inhibitor
What is the function of fibrinogen?
Clot formation
What is the function of haptoglobin?
Binds hemoglobin
What is the function of ceruloplasmin?
Binds copper and oxidizes iron
What are the functions of complement C3?
1) opsonization
2) lysis
What causes increased vasodilation and vasopermability?
Inflammation
Are all immunogens antigens?
Yes
Are all antigens immunogens?
No
What is a distinct difference between immunogens and antigens?
Immunogens successfully stimulate an immune response
What is immunogenicity?
The ability of an antigen to stimulate an immune response
What factors affect the strength of immunogenicity?
1) macromolecule size
2) foreignness
3) ability to be processed and presented with MHC molecules
4) chemical composition
5) molecular complexity
What are the most effective immunogens?
- proteins (strongest)
- polysaccharides
Describe the structure of a proteins primary structure?
- made up of subunits known as amino acids that are covalently linked together in polypeptide chains of various links
describe the structure of proteins secondary structure
Interactions between amino acids within primary structure causes chain to band/kink/loop creating 3D shapes
What are the two common secondary structures found in proteins?
- alpha-helices
- beta-pleated sheets
Describe the alpha helices of the secondary structures of protein
- peptide chains that twist to form a signal
Describe the beta-pleated sheet secondary structure of protein
Chains of undulating zig zags that have a planar shape
Describe the tertiary stucture of proteins
Secondary folds upon themselves once again, bringing distant regions of Amino acid chains together and embodying the 3D orientation of the entire molecule
Describe the quaternary structure of proteins
Two or ore polypeptide chains come together, forming a multimeric unit
What are polysaccharides less immunogenic than proteins?
- their small size
- T cells do not recognize carbohydrates
What are not immunogenic by themselves?
- pure nucleic acids
- lipids
What is required for a substance to elicit an immune response?
- must be subject to antigen processing
What is antigen processing?
- involves enzymatic digestion to create small peptides that can be completed by MHC molecules for presentation to responsiveness of an specific antigen
What is a hapten?
- a substance that isn’t immunogenic by itself but is able to form a new antigenic determinant when combined with larger carrier molecule
Are haptens considered an antigen or an immunogen?
Antigen
What is an epitope?
- part of antigen that hosts immune system recognizes, eliciting the immune response to an invading pathogen
- specifically binds to the corresponding antigen receptor on the immune cell
What are the two types of epitopes that B cells recognize?
1) linear epitopes
2) conformation epitopes
describe linear epitopes
Consist of sequential amino acids on a single polypeptide chain
Describe conformational epitopes
- results from the folding of one or more polypeptide chains, bringing together amino acids that may be distant from each other so that they are recognized together
What is an autoantigen?
- antigens that belong to host
- does not evoke an immune response under normal circumstances
What happens if an immune response does occur to autoantigens?
May result in autoimmune disease
What is an alloantigen?
From other members of the hosts species and are capable of eliciting an immune response
When are alloantigens important to consider?
- tissue transplant
- blood transfusion
What is a heteroantigen?
From other speciesm such as other animals, plants or microorganisms
What is a heterophile antigen?
- heteroantigens that exist in unrelated plants or animals but are either identical or closely related in structures so that an antibody against either antigen will cross- react with each other
Describe current rapid screening tests for IM
- detect heterophil antibodies present in the serum of infected patients that cross react with horse or bovine RBCs antigens
where are MHC molecules found?
On all nucleated cells
What do MHC molecules play a pivotal role in?
- development both humoral and cell-mediated immunity
What is the main immune function of MHC molecules?
- bring antigens to cell surface for recognition by the T cells
- only when the antigens is combined with the MHC molecules does the T cell activation occur
What is B cell recognition?
Surface receptors bind to antigen directly
What is T cell recognition?
Requires antigens to be cradled within MHC molecules
Where are class I MHC molecule genes found?
3 loci’s: A, B, C
Where are class II MHC molecule genes found?
- D region: DR, DQ, and DP
Where are class III MHC molecules found?
Lies between the class I and class II regions on chromosome 6
describe class III MHC molecules
- are secreted protein that have an immune function, but they are not expressed on cell surfaces
What is codominant?
All alleles that an individual inherits code for products that are expressed on cells
What is a haplotype?
- group of alleles in an organism that are inherited together from a single parent
- one haplotype is inherited from each parent
Where cells are class II MHC molecules found in?
Primarily on antigen-presenting cells (APCs)
What are the most important class I MHC antigens to match for transplantation?
- HLA-A antigens
- HLA-B antigens
What are the major class II molecules?
- HLA-DP
- HLA-DQ
- HLA-DR
Describe antigen presentation
- peptide fragments derived from degraded proteins are transported to the plasma membrane, allowing recognition by T lymphocytes
What does the class I MHC molecules mainly present?
CD8 T cells (cytotoxic)
What does the class II MHC molecules mainly present?
CD4 Th cell
What is the function of class I MHC molecule?
Watchdogs of viral, tumor and intracellular bodies
What is the function of class II MHC molecule?
- help to mount an immune response to bacterial infections or other pathogens usually found outside of cells
Describe modern transplant HLA testing
- involves the use of molecular techniques to determine the MHC types of both donor and recipient
What could occur when an individual inherits certain HLA types?
May predispose individuals to the development of autoimmunity
What is rheumatoid arthritis?
Inflammation of multiple joints
Describe type I diabetes
Increase in blood glucose because of destruction of insulin-producing cells
What are two transporters associated with antigen processing?
TAP1
TAP2
What is immunogen?
A substance that reacts with an antibody or sensitized cell but always triggers an immune response
What is an adjuvant?
- substances delivered simultaneously with an antigen to enhance the immune response; used in vaccines
- also prevents antigen from diffusing more immune cells to the injection site of inoculation
What is an allele?
Alernate forms of a gene that code for a slightly different variety of the same product
Where are class II MHC molecules synthesized?
Rough endoplasmic reticulum
Describe helper T cells
- recognize antigen along with class II MHC protein
- orchestrate the adaptive immune response, influencing activities of other immune cells
- express CD4 receptors
What is the key portion of an antigen?
Epitope
How do adjuvants work?
Acts by activating innate immune cells
What is the most polymorphic gene system in humans?
HLA systems
What is the function of cytotoxic T cells?
To kill cells infected with intracellular pathogens, such as viruses, bacteria and cancerous cells
What is the function of Th cells?
- control the immune response through the secretion of cytokines or signaling molecules that allow communication between immune cells
What are the roles of antibodies in immunity?
1) labeling targets for ingestion by phagocytes
2) rendering viruses and toxins inert through neutralization
3) blocking adhesion of microbes to body tissues
Describe clonal expansion when infection occurs
Only lymphocytes responsive to epitopes found on/in the invading pathogens are activated and proliferate
What are effector cells?
Either T cells that secrete cytokines or cytotoxic OR B cells that produce antibodies
Describe memory cells
- enter quiescent state and become long-lived
- lie in wait for reinfection with same microbe
- when they encounter their specific epitope, they activate rapidly, resulting in faster response of greater magnitude that the primary response
Where do thymocytes enter the thymus?
Cortico-medullary junction
What are the stages of T cell differentiation?
- double negative stage
- double positive stage
- mature T cells
What are the 3 pairs that occur in CD3 complex?
- delta-epsilon
- gamma-epsilon
- tau-tau
What type of antigens is not recognized alone by T cell receptors?
Peptide antigens
Where does negative selection occur?
In the corticomedullary and medulla region of the thymus
When is a T cell considered mature?
When it exits the thymus
What is a naive T cells?
- mature T cells that have not yet encounter d the specific peptide epitope recognized by their TCR
What are all B cells derived from?
Hematopoietic stem cells
What is antigen-independent phase?
- first phase of B cell development in bone marrow that results in mature B-cells that have not been exposed to antigens
What are the subpopulations of antigen independent phase?
- pro-B cells
- pre-B cells
- immature B cells
- mature B cells
Describe the antigen dependent phase?
If B cells are stimulated by antigen, it undergoes transformation to a blast stage that forms memory cells and plasma cells
Describe Pro B cells
- stage in B-cell development in which rearrangement of the genes that code for the heavy-chain region of an antibody occurs
- B-cell progenitors receive signals from bone marrow stromal cell to cell contact as well as soluble cytokines
What is the most important event of Pro B cell phase?
Rearrangement of the B-cell receptors (BCR) genes
What do BCR and TCRs have in common?
1) composed of 2 different chains
2) have variable regions which determine their specificity
3) have constant regions, which allow for intracellular signaling activation of the lymphocytes expressing them
4) have a similar gene regions (V, D, J)
5) use similar mechanisms for gene rearrangement
What are the two chains in BCRs?
Light and heavy chains
What genes in BCR contain multiple V, D, and J segements?
Heavy chain genes
What needs to occur for a Pro B cell to progress to the next phase of differentiation?
At least one heavy chain gene must undergo successful rearrangement
Describe the Pre-B cell phase
- the stage of B cell development where the heavy chain part of the antibody molecule is present
What are the two types of light chains possessed by humans?
Kappa
Lambda
What is the first immunoglobulin produced?
IgM
What signifies the Pre-B cells entry into the next phase, immature B cells?
The appearance of a functional BCR on the B cell surface
What determines the antigen specificity of immature B cell and its IgM BCR?
The immunoglobulin variable region, found on both the light and heavy chains
What happens to prevent BCRs from responding to self-antigens?
Negative selection
What occurs when B cells reach maturity?
B-cells respond to binding of antigen to the BCR by activation, proliferation, and antibody production
What is the reaction of immature B cells when signaled?
Halting their development and undergoing apoptosis
Describe central tolerance
- elimination of B cells that bear self-reactive receptors
- it is estimated that more than 90% of B cells die in this manner
What surface markers begin to make an appearance during the immature B cell phase?
- IgM
- CD21
- CD40
- class II MHC
When is a B cell considered mature?
Expresses a functional IgM BCR, survives selection by not reacting to self antigens and begins to display certain B cell markers
What occurs once a B cell is considered mature?
- exit bone marrow and are carried in the blood to the spleen for the next stage of development
What are the two types of mature B cells that develop in the spleen?
- follicular B cells (majority)
- marginal-zone cells
Where can follicular cells be found?
Constantly recirculate between blood and secondary lymphoid organs in search of their specific antigens
Where can marginal-zone B cells be found?
Remain in spleen to respond quickly to blood-borne pathogens
Describe lymphoid follicles
Represent dense clusters of naiver B cells awaiting exposure to their specific antigens
Where are marginal-zone B cells located in the spleen?
Marginal sinus
What does a the presen se of both IgM and IgD on the cell membrane signify?
A mature B cell
What are plasma cells role?
A differentiated B cell that actively secretes antibodies
What is a common resident of bone marrow and the germinal centers of peripheral lymphoid organs?
Plasma cells`
What occurs when an infection occurs in the body tissues?
- macrophages and dendritic cells are among the first immune cells to respond
- APCs engulf pathogens at these distal sites of infection and carry associated antigen to local lymph nodes
What transforms a naive T cell to an activated T cells?
Combination of signals that arises when the TCR recognizes its specific peptide and CD28 is ligated
What are Th cells considered the most important cells of the adaptive response?
- driving activities of other immune cells that act directly fight infection
What are the most prominent subsets of Th cells?
Th1
Th2
Th17
What influences the type of Th cell subset that is produced after differentiation?
Influenced by the cytokines present during activation
Describe role of Th1
-produce IFN-gamma, IL-2, and TNF-alpha which protect cells against intracellular pathogens by activating cytotoxic lymphocytes and macrophages
Describe role of Th2
-essential role is to help B cells produce antibodies against extracellular pathogens and to generally regulate B cell activity
- produces: IL-4, IL-5, IL-6, IL-9, IL-10 and IL-13
- also may play role in allergies
Describe the role of Th17
Produce cytokines IL-17 and IL-22 which lead to the recruitment of granulocytes in response to an extracellular bacterial infection damage
Describe T regulatory cells (Treg cells)?
- subset of T cell
- posses the CD4 and CD25 antigens
- play important role in suppressing the immune response to self-antigens and harmless antigens
How do Treg cells suppress the immune response to self and harmless antigens?
They proliferate of other T cell populations by secreting inhibitory cytokines
What are the two main distinct population created after cell division of Th cells?
1) most Th cells begin to secrete to cytokines and may travel to infected tissues where their activities are most needed
2) a small percentage of Th cells generated after activation will differentiate into memory cells
What are the two toxic substances found in cytotoxic T cell granules?
- perforins
- granzymes
How do T-dependent antigens get their name?
The follicular B cell response depends heavily on the activity of Tfh cells to promote an effective antibody response, antigens that provoke this type of response
How did T-independent antigens get their name?
Marginal-zone B cells don’t require the help of Tfh cells
T-dependent antigens are most likely what?
Proteins, only type of antigen that can stimulate a T cell response
What are the two possible fates of daughter B cells that are produced during proliferative phase of T dependent response?
1) remain in contact with T cells and differentiate into IgM secreting plasma cells
2) others form germinal centers within follicles and participate in a series of processes that enhance the antibody response through time
What are the three overlapping processes of the germinal center formation require?
1) immunoglobulin isotope switching
2) activity maturation
3) memory cell generation
Describe IgG
- predominant form of antibody found in blood
- found in intestines and the bodies secretion
- associated with allergies
What is isotope switching?
- under the direction of T cells, germinal center B cells can change which class of antibody they express
- also determines the class of antibody secreted once the B cell differentiates into a plasma cell
What is affinity maturation?
- immunoglobulin binds antigen with increasing strength (affinity) through the course of an immune response, resulting in the production of even more effective antibodies
- this is accomplished through somatic hypermutation
What is somatic hypermutations?
Appearance of mutations in immunoglobulin gene variable regions
What causes daughter cells to be produced with slightly different antigen-binding abilities
Somatic hypermutation
For each generation of daughter cells produced within the germinal center, there are 3 basic populations of cells formed. What are these cells?
1) plasma cells
2) memory cells
3) B cells hat remain in the germinal center to continue the process of affinity maturation
What occurs once a memory B cell is re-exposed to an antigen?
It can rapidly respond with the production of high affinity, class switched antibody
What are the Pro-B cells key CD markers?
CD10 and CD19
What are the Pre-B cell key CD markers>?
CD10
CD19
CD20
What are the immature B cell key CD markers?
CD10
CD19
CD20
CD21
CD40
What are the mature B cell key CD markers?
CD19
CD20
CD21
CD40
What are the Pro-B cell receptors?
None
What is the Pre-B cell receptor
Pre-BCR: immunoglobulin heavy chain and surrogate light chain
What is the immature B cell receptors?
Functional BCR: IgM heavy chains and kappa or lambda light chains
What is the mature B cell receptor?
Functional BCR: IgD or IgM gravy chains and kappa or lambda light chains
What is the double negative key CD marker?
CD3
What is the double negative key CD marker?
CD3
What is the double negative T cell receptors?
None
What are the double positive key CD markers?
CD3
CD4
CD8
What are the double positive T cell receptors?
TCR alpha
TCR beta
What are the single positive key CD markers?
CD3
CD4
CD8
What are the single positive T cell receptors?
TCR alpha
TCR beta
What is a characteristic of immune response to a T-independent antigen?
- antigen are often polysaccharides
How does the humoral immunity produce antibodies?
By plasma cells
What is negative selection?>
- process that takes place among surviving DP T cells in the corticomedullary region and the medulla of the thymus
- strong reactions with self-peptides other than MHC antigens triggers apoptosis
What are thymocytes?
Lymphocyte precursors in the thymus that are committed to becoming T cells
Describe immature B cells
A phase in the growth of B cells characterized by the appearance of complete IgM antibody molecules on the cell surface
What are variables?
- contained by both alpha and beta chains on TCR
- recognizes specific antigens
What is MHC restriction?
Selection of thymocytes that will only interact with the MHC antigens found on host cells
What is a surrogate light chain?
- consists of two short polypeptide chains that are noncovalently associated, along with two shorter chains, Ig-alpha and Ig-beta
What is allelic exclusions?
Selection of an allele on one chromosome only
What is clonal deletion?
Process of elimination of clones of cells that would be capable of an autoimmune responses
Describe Flow cytometry
Automated system for identifying cells based on the scattering of light as cells flow single file in a stream of fluid by a laser beam
What is positive selection?
allows only DP cells with functional TCR receptors to survive
What is a distinguishing feature of Pre-B cells?
Mu chains in the cytoplasm
What are the 3 characteristics of acute phase reactants?
1) rapid increase following infection
2) enhancement of phagocytosis
3) nonspecific indicators of inflammation
What are 3 characteristics of an immunogen?
1) large molecular weight
2) internal complexity
3) presence of numerous epitopes
Where are class II MHC ANTIGENS found
B cells
macrophage
What is an immunoglobulin?
Globular proteins (glycoproteins) that play a role in immunity
What is the composition of immunoglobulins?
- 86-98% polypeptides
- 2-14% carbohydrates
What percentage of plasma proteins are immunoglobulins?
20%
Describe serum protein electrophoresis procedure
1) serum is placed on a agarose gel
2) electric current applied to separate the proteins
At what pH does electrophoresis separates most serum proteins by size and change?
8.6
What do the results of electrophoresis appear as?
Five bands
What are the slowest moving protein?
Immunoglobulins
What band of electrophoresis contains the most antibody activity’?
Gamma band
What are the 5 classes of immunoglobulins?
IgG
IgM
IgD
IgE
IgA
Describe the two dimensional forms of IgG
- two large peptide chains (heavy chains, unique)
- two small peptide chains (light chains, kappa or lambda)
How do the kappa and lambda light chains differ?
- differ by just a few amino acid substitutions along their length
- no functional difference
What are heavy and light chains held together by?
- Disulfide bonds (s-s)
- hydrogen bonds
- hydrophobic forces
- electrostatic attractions
What is the structural unit of all the immunoglobulin classes?
Tetrapeptide structure
Where is the variable region of an immunoglobulin located?
The first 110 amino acids of the molecule at the amino terminal
Describe the variable region of an immunoglobulin
- unique to each other antibody
- allows the molecule to bind specifically to a particular antigen
Where is the constant region of the immunoglobulin located?
From amino acid 111 to the carboxyl terminal
Describe the constant region of an immunoglobulin
- are the same in each immunoglobulin class/subclass
- responsible for the biological functions that play a role in immune defense against an antigen
What are the three constant regions of an immunoglobulin?
CH1
CH2
CH3
What are CH2 and CH3 responsible for?
For binding to complement and Fc receptors on phagocytic cells
What are the prototypic enzymes?
Pepsin and papain
Describe Papain
- cleaves the IgG molecule below the set of the disulfide bonds that holds the two heavy chains together, resulting in formation of 3 fragments: 2 Fab fragments and Fc fragment
Describe Fab fragments
- each have one light chain and one half of a heavy chain
- located at amino-terminal end o the molecule
- both are identical
- have antigen-binding capability
Describe the Fc fragment
- consists of carboxyl-terminal halves of two heavy chain
- spontaneously crystallizes at 4 C
- does not bind antigen
- contain constant regions CH2 and CH3
Describe pepsin
- cleaves IgG at the carboxyl-terminal side of the inter chain disulfide bonds
- 2 fragments: F(ab’)2 fragment and Fc’
Describe the F(ab’)2 fragment
- contains all antigen binding ability in pepsin
Describe Fc’ (fragment of pepsin)
- in carboxyl-terminal portion of the molecule which is disintergrated into several smaller pieces
- has no biological activity
Describe the hinge region of an immunoglobulin
- segment of heavy chain located between the CH1 and CH2
- rich in hydrophobic residues
- high proline content that allows for flexibility
What is flexibility important in the hinge region of immunoglobulin?
- let’s two antigen binding sites operate independently and engage in angular motion relative to each other and to the Fc stem
- initiation of complement cascade
- binding to cells with specific receptors for the Fc portion of molecule
What immunoglobulins have a hinge region?
IgG
IgD
IgA
Why do IgM and IgE gave flexibility even though they do not have a hinge region?
CH2 are paired in such a way as to confer flexibility to the Fab arms
What do immunoglobulins contain>?
4 polypeptide chains
Carbohydrate portion
Where is the carbohydrate portion of immunoglobulins located?
Between the CH2 domains of the two heavy chains
What are the functions of the carbohydate portion of immunoglobulins?
1) increase solubility of immunoglobulin
2) provide protection against degradation of molecule
3) enhancing functional activity of Fc domain (most important)
What are the three antigenic determinants?
Isotype
Allotype
Idiotype
describe isotype
- unique amino acid sequences that are common to all immunoglobulins of given class/subclass
- identical in all individuals or given species and differ from one species to another
How can antibodies to human isotypes be prepared?
By immunizing animals with human serum
What are allotypes?
- minor variations of amino acid sequences that are present in some individuals of the same species but not others
What classes do allotypes occur in?
- four Ig classes
- one IgA subclass
- lambda light chain
Where are allotypes located in an immunoglobulin?
- found in the constant region
What are idiotypes?
- the variable portion of each immunoglobulin chain are unique to a specific-antibody molecule
- essential to the formation of the antigen binding site
Where are idiotypes located in the immunoglobulin?
At the amino-terminal ends of both heavy chains and light chains
What is the predominant immunoglobulin in humans?
IgG
What % of immunoglobulins are IgG?
70-75%
What immunoglobulin has the longest half life?
IgG
Describe structure of IgG
- monomer
- consists of one tetrapeptide unit
What are the 4 subclasses of IgG? What is their compositions?
IgG1: 66%
IgG2: 23%
IgG3: 7%
IgG4: 4%
What are IgG1 and IgG3 associated with?
Protein antigens
What are IgG2 and IgG4 associated with?
Polysaccharide antigens
What immunoglobulins can cross the placenta?
IgG (except IgG2)
What are the functions of IgG?
1) CH2 region is able to bind to complement
2) important mediator of opsonization
3) participates in antibody-dependent cellular cytotoxicity
4) ability to bind to bacterial toxins and viruses and neutralizes their activity
5) can cross placenta
6) agglutination reactions and precipitation takes place in vitro
What does activation of complement result in?
An enhanced inflammatory response and destruction of foreign cells such as bacteria
What is the most efficient subclass of IgG to bind completeIgM? Why?
IgG3: it has the largest hinge region and the largest number of interchain disulfide bonds
What is the 2nd most efficient subclass of IgG to bind complement
?
IgG1
What is opsonization?
The coating of a foreign antigen that leads to enhanced phagocytosis
Why are IgG1 and IgG3 particularly good opsonins?
They bind most strongly to Fc receptors
Why is passive transfer of maternal IgG to the fetus important?
Providing immunity to the newborn during its first few months of life, when its immune system is immature
Is IgG better at agglutination or precipitation? Why?
Precipitation because it involves small soluble particles, which are brought together more easily by the relatively small IgG molecule
What else is IgM called? Where does it get this name?
Macroglobulin because it is the largest of all the immunoglobulin classes
Describe the structure of IgM
- pentameter of five monomers held together by J chain (joining)
Describe J chain
- glycoprotein that holds together monomers
- cysteine residues form disulfide bonds that link the carboxyl-terminal ends of adjacent monomers in IgM and IgA
What does each monomer of IgM contain?
- Mu heavy chains and either kappa or lambda chains
- Mu heavy chains possess one more constant domain (CH4) adding to it large size
What % of immunoglobulins are IgM?
5-10%
What does IgM perform things more efficiently than IgG?
Because of IgMs multiple binding sites
What immunoglobulin is most efficient at triggering the classical pathway?
IgM because a single molecule can initiate the reaction when complement binds to two adjacent CH region
Where are IGN mainly found?
In the intravascular pool and not in other body fluids or tissues because of its large size
What immunoglobulin is the first to appear after antigenic stimulation?
IgM
What is the first immunoglobulin that appears in maturing infants?
IgM
How many binding sites does IgM have?
10
What % of immunoglobulins are IgA?
10-15%
Where does IgA migrate in electrophoresis?
Between the beta and gamma bands
What immunoglobulins have complement fixation?
IgG
IgM
Describe the basic structure of IgA
- alpha heavy chain
- contains one variable regions
- contains three constant regions
- dimer, two monomers held together by J chain
What are the two subclasses of IgA?
IgA1
IgA2
How do IgA1 and IgA2 differ?
By 22 amino acids, 13 of which are located in hinge region (deleted in IgA2)
Where are IgA2 found?
- secretions at mucosal surfaces
- along respiratory, urogenital, and intestinal mucosa
- appears in breast milk, saliva, tears, sweat, and colostrum
Where are IgA1 found?
In serum
What is the major role of serum IgA?
- anti-inflammatory agent
- down regulate IgG mediated phagocytosis, chemotaxis, bactericidal activity, and cytokine release
Why is the J chain essential for in IgA?
Essential for polymerization and secretion of IgA
Where are secretory IgA synthesized?
Plasma cells found mainly in mucosal-associated lymphoid tissue and is released dimeric form
Describe secretary component
- serves as specific receptors for IgA
- precursor is present on surface of epithelial cells
Where do plasma cells secret IgA>?
Subepithelial tissue
What happens once IgA bind to SC precursors?
- Transcytosis
- both of them are taken inside the cell and released at the opposite surface
What is the main function if secretory IgA?
- to patrol mucosal surfaces and act as a first line of defense by preventing farther into the body
What is the important role of IgA?
- neutralizing toxins produced by microorganisms and helps prevent bacterial and viral adherence to mucosal surfaces
What immunoglobulin complex is trapped by mucus and coughed/sneezed out to protect the respiratory system?
IgA complex
Where is IgA found in humans?
Breast milk
How does breastfeeding help to maintain the health of newborns?
Passively transferring antibodies
What cells posses specific receptors for IgA?
Macrophages
Monocytes
Neutrophils
What % of immunoglobulins are IgD?
0.001%
What is the half day of IgD?
1-3 days
What antibody migrates as fast as a gamma protein?
IgD
Describe hinge region of IgD
- unusually long
- 58 amino acids
Why is IgD more susceptible to proteolysis that any other antibody?
Because of its long hinge region, this may be the reason for its short half life
Where are most IgD found?
Surface of unstimulated B cell
What is the second antibody that appears during an immune response?
IgD
What are the roles of IgD?
- B cell maturation and differentiation
- not exactly understood
Why is IgD an ideal early responder?
High level of surface expression and its intrinsic flexibility
What is IgE best known for?
Very low concentration in serum and the fact that it has the ability to activate mast cells and basophils
What % of immunoglobulins are IgE?
0.0005%
Describe the IgE structure
- epsilon heavy chain is composed of one variables and four constant domains
- a single disulfide bond joins each epsilon chain to a light chain, and two disulfide bonds link the heavy chains to one another
Does IgE participate in complement fixation, agglutination, or opsonization?
None of them
Where can plasma cells that produce IgE be located?
Primarily in lungs and in the skin
Where can mast cells be located?
- mainly in the skin
- lining of the respiratory and alimentary tracts
What does the release of IgE mediators induce?
- type I hypersensitivity
- allergic reaction
What are typical reactions with allergic reactions?
- anaphylactic shock
- asthma
- diarrhea
- hay fever
- hives
- vomiting
Describe the role of IgE
Serve a protective role by triggering an acute inflammatory reaction that recruits neutrophils and eosinophils to the area to help destroy invading antigens that have penetrated IgA defenses
What occurs when the first time an individual is exposed to an antigen?
Primary antibody response
What are characteristics of primary antibody response?
- IgM shows up first
- lag phase between the encounter with the antigen and the production of detectable antibody
- low affinity
- amount of antibody produced are relatively low and decline during the span of a few weeks
Describe the lag phase of the primary antibody response
- lasts 4 and 7 days
-T and B cells are being activated to respond to the antigen by the T-dependent mechanisms of antibody production
What does the lag phase of the primary antibody response result in?
Results in the generation of antibody-secreting plasma cells
What do activated B cells from the primary response develop into?
- plasma cells
- expand into clones of memory cells (long lived)
Describe secondary antibody response?
If memory cells are exposed to the same antigen weeks, months, or even years later, they can rapidly differentiate into plasma cells and larger amounts of antibody are produced
What are characteristics of the secondary antibody production?
- shorter lag time: 1-2 days
- high affinity
- production of low levels of IgM that rapidly declibe
- higher levels of other immunoglobulin isotypes, mainly IgG levels decline slowy and persists for longer periods
Describe clonal selection hypothesis
- body has numerous close of lymphocytes, each possessing surface receptors with a unique specificity
- when body is exposed to antigen, the antigen selectively binds to receptors on cells to proliferate and mount antibody responses
When can a gene be transcribed and translated into functional antibody molecule?
Not until it undergoes rearrangement, assisted by special recombinase enzymes
What does gene rearrangement involve?
Cutting and splicing process that removes much of the intervening DNA, resulting in a functional gene that codes for a specific antibody
Where does rearrangement of the gene begin?
The heavy chains
What are the genes that code for variable region of the heavy chain divided into?
Divided into 3 groups;
- V genes (variable) —> 45 genes
- D genes (diversity) —> 23 genes
- J genes (joining) —> 6 genes
Where are all the V,D and J genes present?
The germ line DNA of a bone marrow stem cell
Joining of V, D, J and constant region of a heavy chain is a two step process. What are the steps?
1) In Pro-B cells, one D gene and one J gene are randomly chose and are joined by means of a recombines enzyme after the intervening DNA is deleted
2) in Pre-B cells, a V gene is joined to the DJ complex, resulting in a rearranged VDJ gene
What is allelic exclusion?
The genes on the second chromosome are not rearranged because the rearrangement of DNA on one chromosome 14 was successful the first time
What occurs is the first rearrangement of heavy chains is unsuccessful?
- rearrangement of the second set of genes on the other chromosome 14 occurs
- this mechanism maintains clonal specificity by ensuring each B cell only expresses a single antigen receptor
What happens after rearrangement of the genes of the heavy chains?
- the variable and constant regions are joined
- occurs at the RNA level, thus conserving the DNA of the constant regions
What are the markers of the Pre-B cells?
Mu heavy chains
What does the presence of both C”Mu” and C”delta” regions of heavy chains allow?
Allows for mRNA for IgD and IgM t be transcribed at the same time
When do light chains rearrangement occur?
After Mu chains appear
Describe VJ joining of light chains
- accomplished by cutting out one intervening DNA
- results in the V(k) and J(k) segments becoming permanently joined to one another on the rearranged chromosome
When does lambda chain synthesis occur in a light chain?
Only it a nonfunctioning gene product arises from Kappa rearrangement
What does the lambda locus consist of?
Approximately:
- 30 V(lambda) segments
- 4 J(lambda) segments
- 4 C(lambda) segments
If functional heavy and light chains are not produced but a B cell, what occurs?
Cell dies by apoptosis
Light chains are joined with Mu chains to form what?
- a complete IgM antibody
- first appears in immature B cells
What happens once IgM and IgD are present on the surface membrane?
The B cell is fully mature and capable of responding to antigen
What are essential for initiating the VDJ recombination during B cell maturation?
Recombinase enzymes
RAG-1
RAG-2
What is the role of RAG-1 and RAG-2?
Recognize specific recombination signal sequences in the DNA that flank all immunoglobulin gene segments
What is junctional diversity?
- V, D and J segments doesn’t always occur at a fixed position, so each sequence can vary by small number of nucleotides
- major contributor to diversity in the variable-region genes
Where do immunoglobulins get their variation diversity from?
1) junctional diversity
2) different heavy chains can combine to different light chains
3) somatic hypermutation
What is class switching?
A the immune response progresses, B cells, may become capable of producing antibody of another class
What is switch recombination?
- a portion of the constant region DNA is deleted and the remaining C(h) genes are placed adjacent to the variable to the variable region genes
- allows the same VDJ region to be coupled with a different C regions to produce-antibody of a different class but having identical specificity for antigen
What are monoclonal antibodies?
- derived from singe antibody-producing cell that has reproduced many times to form a clone
- all the cells in the clone are identical and the antibody produced is exactly the same
-directed agains a specific epitope
what is hybridoma?
- fusion of activated B cell and myeloma cell
- myeloma cell chosen lacks essential enzymes and cannot produce own antibodies
How does production of hybridomas begin?
By immunizing a mouse with the desired antigen
What is the traditional process of mouse antibody production?
1) immunize a mouse with a specific-antigen
2) harvest spleen cells from the mouse spleen
3) combine spleen cells with myeloma cells in the presence of PEG
4) select fused cells and screen for presence of desired antibody
5) grow positive cells in larger quantities
What was used before monoclonal antibodies?
- antibody reagent could only be produced by immunizing animals such as horses or goats with the desired antigen and isolating polyclonal antibodies from the animal serum
What are the primary advantages of the monoclonal antibody reagent?
- provide decreased lot-to-lot variaton
- increased specificity toward a single epitope, rather than multiple epitopes of an antigen
What is a major limitation of using mouse monoclonal antibody as therapeutic agents?
- highly immunogenic for humans, inducing the development of human anti-mouse antibodies (HAMAs) that can cause severe hypersensitivity reactions
Where are isotypes located?
Constant region
Where are allotypes located?
In the constant regions of the IgG subclasses, one IgA subclass, and light chain
Where are idiotypes located?
Amino terminal regions of heavy and light chains
Where do antigens bind on immunoglobulins?
Hypervariable regions that contain CDRs
What are complement fixation functions?
1) enhances inflammatory response
2) uses positive feedback cycle to promote phagocytosis
3) enlists more defensive elements
Explain the process of complement fixation
1) antibodies bound to cells change shape and expose complement binding sites
2) this triggers complement fixation and cell lysis
Describe neutralization of antibody action
Antibodies bind to and block specific sites on viruses or exotoxins, thus preventing these antigens from binding to receptors on tissue cells
Describe agglutination of antibody action
- makes antigen-antibody complexes that are cross-linked, causing clumping
Describe precipitation of antibody action?
- soluble molecules are cross-linked into large insoluble complexes
What enhances phagocytosis at the antigen-antibody complex?
- neutralization
- agglutionation
- precipitation
- complement
What enhances inflammation of antigen-antibody complex? co
Complement
What are cytokines?
- chemical messengers that regulate immunity
- small proteins that bin to and activate receptors located on the target cells
Describe regulations of cytokines?
- Important in determining where cytokine action will be effective or inappropriate
- massive overproduction and dysregulation of cytokines can lead to yperctokinemia
- results in hypotension, fever, edema, multi-organ failure, or death
What is pleitotropy?
Single cytokine with many different actions
What is redundancy?
- occurs when different cytokines activate some of the same pathway and genes
- can be explained by the fact many cytokines share receptors subunits
How is cytokine activity classified?
According to the distance traveled between the producing cell and its targets cells
What is autocrine?
Cytokines that bind to receptors on the same cell from which they were secreted
What is a paracrine?
Cytokines that act one cells within tissue region surrounding their cellular source
What is an endocrine?
Some cytokines diffuse into the bloodstream, allowing them to influence cells far from the cells that produce them
What is synergistic?
Interactions that complement and enhance each other
What is antagonism?
If one cytokine counteracts the action of another
What is a cytokine cascade?
Many cytokines induce the production of additional cytokines by targeting cells
What is the antagonist of IL-4?
TNF-alpha
What synergies with IFN-gamma?
TNF-alpha
What is hypercytokinemia?
- also referred to as cytokine storm
- massive overproduction and dysregulation of cytokines can result in hyper stimulation of the immune response
What are the major proinflammatory cytokines?
- TNF-alpha
- IL-1
- IL-6
- IFN-gamma
What are the major anti-inflammatory cytokines?
- TGF-beta
- IL-10
- IL-13
- IL-35
What is the most important role of IL-1, IL-6, and TNF-alpha?
Recruiting effector cells, such as neutrophils and monocytes, into inflamed tissues
What are the best characterized cytokines of the IL-1 family?
IL-1alpha
IL-1beta
IL-1RA
Describe IL-1 alpha
- retained within the cell cytoplasm
- only released after cell death
- presence of IL-1alpha helps attract inflammatory cells to areas where cell and tissues are being damaged or killed
Describe IL-1beta
-mediates most paracrine (local) and hormonal (sytstemic) activity
- before secretion, IL-1beta must be cleaved intracellularly to an active form
Why is IL-1beta referred to as endogenous pyrogens?
It’s ability to induce fever
What purpose does a fever have?
1) inhibit of many bacteria and fungi.
2) increase the microbicidial activities of macrophages and neutrophils
3) contribute to feeling of discomfort and fatigue, compelling individuals to rest
What are the role of IL-1beta?
1) activation of phagocytosis
2) induce fever
3) production of acute-phase reactant
What are TNF products of?
Macrophages and lymphocytes
Describe CD40 ligand
Essential for signaling between T and B cells
What is the most important TNF of inflammation?
TNF-alpha
What is a major inducer of TNF-alpha production?
Microbial substances such as LPS
What is LPS?
A component of the cell wall of gram-negative bacteria
The activity of IL-6 is highly ________.
Pleiotropic
What are innate roles of IL-6?
- stimulates the production of acute-phase proteins by liver hepatocytes
What are the adaptive roles of IL-6?
- increases activation of B and T cells
- causes B cells to proliferate and differentiate into plasma cells
What are chemokines?
Subgroup of cytokines that influence the motility and migration of their tartlet cells
What are the 4 families of chemokines?
1) CXC
2) CC
3) C
4) CX3C
Describe CXC chemokines
Contain single amino acid between the first and second cysteines
Describe CC chemokines
The cysteines are found together, with no intervening amino acid
Describe C chemokines
Has only a single cysteine
Describe CX3C chemokines
Have 3 amino acids between the cysteines
What is the most important effect of chemokines?
- recruitment of leukocytes from the blood into infected or damaged tissues
What are interferons?
Soluble substances produced by virally infected cells that interfere with the ability or viruses to replicate by making host cells less hospitable to viral takeover
What are the 3 groups of IFNs?
Type I
Type II
Type III
What are the most important cytokines in response to viral infections?
IFN- alpha
IFN-beta
(Both type I)
What are the functions of type I IFN?`
1) interfere with viral replication
2) activate NK cells
3) enhances expression of class I MHC proteins on target cells
What is the most important innate defense mechanism against viral infection?
Combination of IFN-alpha and IFN-beta and NK cell killing
What secretes the majority of the cytokines in the adaptive immunity?
T cells, especially T helper Cells (CD4+)
What are the 4 sub populations of T helper cells?
Th1
Th2
Th17
Treg cells
Describe differentiation of Th cells
The cells undertake a process during which they are transformed into one of the four subclasses
What causes differentiation to the Th1 lineage?
Dendritic cell production of cytokine IL-12
What drives antibody mediated immunity?
IL-4
What arises in the presence of IL-23?
Th17 cells
What are produced in response to TGF-beta?
Treg cells
what is the hallmark of Th1 cells?
High level expression of the proliferative cytokine IL-2 and IFN-gamma, a type II IFN
What are the roles of Th1 cells?
1) expand to combat infection with viruses and intracellular bacteria
2) promote cell-mediated immunity with cytotoxic T cells, and activate macrophages
3) cause antigen-activated B cells to produce IgG1 and IgG3 antibodies capable of opsonization and fixing complement
What is another name for IL-2?
T-cell growth factor
What are the roles of IL-2?
1) drives proliferation and differentiation of both T and B cells
2) enhances the lytic activity of NK cells
3) causes naive Th to differentiate into Th1 cells
What is the primary cytokine of the Th1 response?
IFN-gamma
What are the roles of IFN-gamma?
1) influences expression of more than 200 target-cell genes
2) stimulates antigen presentation by class I and class II MHC
3) potent activator of macrophages
4) involved in regulation and activation of CD4+ Th1 cells, CD8+ cytotoxic T cells and NK cells
What are the most influential Th2 cytokines?
IL-4
IL-10
What is the IL-4 activity on naive T cells?
- turns on genes that generate Th2 cells and turns off genes that promote Th1 cells
What are Th2 cells responsible for regulating?
Allergies
Autoimmune disease
Parasites
What does IL-5 do along with IgE?
Drives differentiation and activation of eosinophils in both allergic immune response and responses to parasitic infection
What does IL-4 and IL-13 have in common?
- induce worm expulsion
- favor IgE class switching
How do IL-4 and IL-13 differ?
IL-13 plays anti-inflammatory role by inhibiting activation and cytokine secretion by monocytes
What are the roles of IL-10?
1) has anti-inflammatory and suppressive effects on Th1 cells
2) inhibits antigen presentation by macrophages and dendritic cells
3) down regulates immune response by counteracting IFN-gamma
What is the antagonist of IFN-gamma?
IL-10
How can Treg cells be identified?
Expression of CD4, CD25, and FoxP3
What are Treg cells essential?
For establishing peripheral tolerance to a wide variety of self-antigens and harmless antigens
What are the roles of Treg cells?
1) establish peripheral tolerance to self-antigens and harmless antigens
2) produce suppressive cytokines: TGF-beta and IL-10
3) down regulate immune response to prevent chronic inflammation (main)
4) may prevent tumor cells from attack by inhibiting cancer-fight cells
What does Th17 secrete?
IL-17 family cytokines
What cytokines play a role in finalizing the commitment to Th17?
IL-23
What are the roles of Th17?
1) host defense against bacterial and fungal infection at mucosal surfaces
2) secretion of IL-17
3) promote recruitment of neutrophils
4) promote release of antimicrobial peptides
5) when dysregulated, may promote pathogenesis of several inflammatory dieases
What are the APC cytokines?
IL-12
IL-23
What are the primary mediators of hematopoiesis called? Why?
- IL-3
- EPO
- G-CSF
- M-CSF
- GM-CSF
Why does IL-3 act one bone marrow stem cells?
To begin differentiation cycle
What happens if M-CSF is activated?
The cells become macrophages
What is the role of M-CSF?
Increases phagocytosis, chemotaxis, and additional cytokine production in monocytes and macrophages
What happens if G-CSF is activated?
Cells become neutrophils
What are the roles of G-CSF?
1) enhances function of mature neutrophils
2) affects the survival, proliferation, and differentiation of all cell types in neutrophil lineage
3) decreases IFN-gamma production
4) increases production IL-4 in T cells
5) mobilizes multi potent stem cells from the bone marrow
What does GM-CSF do?
Acts to drive differentiation toward other WBC types
What does EPO do?
Regulate RBC production in the bone marrow
What is EPO mainly produced by?
The kidneys
What is recombinant EPO?
- administered to improve RBC counts for individual with anemia and those with cancer
What is anti-cytokine therapy?
Aims to break vicious cycle of chronic inflammation by targeting the interactions between specific cytokines cytokines and their cognate receptors
Describe newer anti-cytokine agents
Greatly improved using recombinant DNA techniques to generate humanized monoclonal DNA antibodies that are much less immunogenic
What are 3 cytokine assay formats?
1) ELISAs
2) microbead assays
3) ELISpot assays
Describe ELISAs
- can detect many pro- and anti- inflammatory cytokines in one reaction
- allow for simultaneous detection of several cytokines from serum or plasma in single a test run
- has “spots”
Describe microbead assays
- allow for the simultaneous detection of multiple cytokines in a single tube
- each bead type has own fluorescent wavelength. When combined with fluorescent secondary antibody bound to a specific cytokine, allows for detection stop to 100 different analysis in one tube
Describe ELISpot
- similar to ELISA performed on in vitro activated peripheral WBC
- allow the detection and enumeration of individual cytokine-specific capture antibodies
What is the ELISpot procedure?
1) PBMCs are added to the wells of antibody-coated micro plate and treat with synthetic protein antigen
2) incubation period: Th1 cells secrete cytokines as they rest as the rest at the bottom of the microplate well
3) PBMCs and any soluble substances (cytokines) are washed from wells
4) detection antibody antibody specific to the target cytokine, is added to wells
What is the role of ELISpot detection antibody?
To produce a signal indicating where target cytokine is bound to capture antibody
What do the “spots” represent in ELISpot?
Tiny, elliptical silhouettes of captured IFN-gamma speckling plate bottom
What is PCR product?
Made using fluorescent-labeled primer and can be hybridized to either solid or liquid phase arrays
Describe the solid-phase array of PCR
- have up to 40,000 spots containing specific single-stranded DNA (ssDNA) oligonucleotides representing individual genes
- fluorescence of a spot indicates that gene was expressed in the cell and that cell was producing the cytokine
Describe liquid arrays of PCR
- uses same beads as microbeads arrays but have oligionucleotides on surfaces instead of antibodies. Show up to 100 different complementary DNAs to be identified
- combination of bead fluorescence and fluorescence of labeled cDNA produces an emission spectrum that identifies the cytokine gene that was expressed in cell
What are 4 approaches to anti-cytokine therapy?
1) disrupting interaction between cytokines and their cognate receptors
2) using monoclonal antibodies that function as cytokines agonists
3) hybrid proteins containing cytokine receptor binding sites attacked to Ig constant regions to block cytokine activity
4) blocking IL-17 function
What are Th2 cells involved in?
Antibody-mediated responses
What are Th1 induced by?
Dendritic cell production of IL-12
What are Th2 induced by?
IL-4
What are Th17 induced by?
IL-23
What are treg cells induced by?
TGF-beta
What are the roles of chemokines?
1) enhance motility and promote migration of many types of WBC toward source of the chemokines (chemotaxis)
2) modulate adhesion of WBCs to endothelial cells lining the blood vessels, facilitating extravasation into the tissues
Describe TNF-alpha
- LPS is a major trigger of TNF-alpha production
- secreted by activated monocytes and macrophages
- cause vasodilation and increased vasopermeability
- activates T cells by inducing expression of MHC class II molecules, vascular adhesion molecules and chemokines
What are the roles of complement?
1) causes lysis of foreign cells
2) acts as opsonins
3) increase vascular permeability
4) recruit monocytes and neutrophils to the area of antigen concentration
5) trigger secretion of immunoregulatory molecules that amplify the immune response
What is complement?
A series of more than 50 soluble and cell-bound proteins that interact to enhance host defense mechanisms against foreign cells
What are the three pathways of complement system activation?
1) classical
2) alternative
3) lectin
Describe classical pathway
- involves 9 proteins that are trigger primarily by antigen-antibody complexes
- major role in natural defense system
What classes of immunoglobulins activate the classical pathway?
IgM
IgG1
IgG2
IgG3
Describe recognition unit of the classical pathway?
Formation of C1
Describe activation unit of classical pathway
Once C1 is bound, C4, C2, and C3 are activated
Describe membrane attacks complex (MAC)?
- comprises of C5 through C9
- completes lysis of foreign particles
Describe C1 of classical pathway
- consists of 3 subunits: C1q, C1r, and C1s
- subunits require calcium to maintain structure
What happens once the classical pathway is activated?
C1r cleaves a thioester bond on C1s, which in turn, activates it.
What does it mean when C1s activated?
Recognition stage ends
What marks the beginning of the activation unit of the classical pathway?
Begins when C1s cleaves C4
What marks the end of the activation unit in the classical pathway?
The production of the enzyme C3 convertase
What is the second most abundant complement protein?
C4
What is the combination of C4b and C2a called?
C3 convertase
What occurs if C3 does not bind quickly?
Cleaved into two fragments, C3a and C3b
What is the central constituent of the complement system?
C3
What is the most significant step of complement system?
Cleavage of C3 to C3b
Describe structure of C3
- consists of two polypeptide chains, alpha, beta
- alpha chain highly reactive thioster beta
What occurs after cleavage of C3 in the classical pathway?
About 200 molecules are split for every molecule of C4bC2a
C3b also serves as a powerful _______
Opsonin
What has a specific receptors for C3b? Explain
Macrophages, primed to phagocytize antigen that has bound to C3b
Where does C3b bind in classical pathway? What does this create?
- within 40 nm of the C4bC2a
- C4C2aC36 is created. Also called C5 convertase
Describe the structure of C5
- contains two polypeptide chains, alpha, and beta, which are linked by disulfide bonds to form a molecule
What are the two fragments is C5 split into?
C5a and C5b
What occurs when sC5b-9 is formed in the classical pathway?
- MAC produce a pole of 70 to 100A that allows ions pass in and out of the membrane
What diseases are associated with abnormal C1q, C1r, and C1s?
SLE, recurrent infections
What is the function of C1q?
Binds to Fc region of IgM and IgG, synaptic pruning
What is the function of C1r?
Activates C1s
What is the function of C1s?
Cleaves C4 and C2
What is the function of C4?
Part of C3 convertase (C4b)
What is the function of C2?
- binds to C4b —> forming C3 convertase
What is the function of MBL?
Binds to mannose
What is the function of MASP-1?
Unknown
What is the function of MASP-2?
Cleaves C4 and C2
What is the function of factor B?
Binds to C3b to form C3 convertase
What is the function of factor D?
Cleaves factor B
What is the function of properdin?
Stabilizes C3Bb-C3 convertase
What is the function of C3?
Key intermediate in all pathways
What is the function of C5?
Initiates MAC
What is the function of C6?
Binds to C5b in MAC
What is the function of C7?
Binds to C5bC6 in MAC
What is the function of C8?
Starts pore formation on membrane
What is the function of C9?
Polymerizes to cause cell lysis
What are the steps of the classical pathway?
(Recognition unit)
1) the zygomens C1r and C1s are converted into active enzymes as binding of C1q occurs
2) autoactivation of C1r results from change that takes place as C1q is bound
3) when activated, C1r cleaves thioster bond on C1s, which activates it.
(Activation unit)
4) C1s cleaves C4 to create C4b and C2 to make C2a
5) C3 convertase (C4b2a) is formed
6) C3b binds to C4b2a to form C5 convertase (C4b2a3b)
(MAC)
7) C5 convertase splits C5 into C5a and C5b
8) C5b attaches to the cell membrane to initiate formation of the MAC (C5b6789)
How does the lectin pathway play an important role in infancy?
Defense mechanism during the interval between the loss of maternal antibody and the acquisition of as full-fledged antibody response to pathogens
What are the 3 recognition molecules of the lectin pathway?
- Lectin
- ficolins
- collectins (CL-L1)
What is the key protein of the lectin pathway? Describe this protein
- Mannan binding lectin (MBL)
- binds to mannose or other related sugars in a calcium-dependent manner to initiate this pathway
- considered acute phase protein because produced in liver and normally present in serum
What are the steps of the lectin pathway ?
1) binds to mannose or ribose sugar to initiate pathway
2) complex associates with MASP-1, MASP-2, and MASP-3. Complex act like C1qrs
3) MASP-2 cleaves C4 and C2
4) C3 convertase (C4b2a) is formed
5) C3b binds to C4b2a to form C5 convertase (C4b2a3b)
6) C5 convertase splits C5 into C5a and C5b
7) C5b attaches to the cell membrane to initiate formation of the MAC (C5b6789)
What are the steps of alternative pathway?
1) C3 hydrolysis water to produce C3b which binds Factor B, and together they attach to target cell surface
2) B is cleaved by Factor D into the fragments Ba and Bb. Bb combines with C35 to form C3bBb,an enzyme with C3 convertase activity
3) more C3 is cleared, forming more C3bBb. This enzyme is stabilized by properdin and, it continues to cleave additional C3
4) it a molecule of C3 remains attached to the C3bBbP enzyme, the convertase now has the capability to cleave C5. The C5 convertase now has the capability to cleave C5. The C5 convertase this consists of C3bBbP3b
5) C5b attaches to the cell membrane to initiate formation of MAC (C5b6789)
What is the role of the alternative pathway?
Functions largely as an amplification loop for activation started for activation started from the classical or lectin pathways
What are some triggering substances for the alternative pathway?
- bacterial cell walls
- some parasites
- fungal cell call
- viruses/ viral infected cells
- tumor cell line
- yeasts
- these all serve as binding site complex C3bBb
What proteins are involved in the alternative pathway?
- C3
- C5-C9
- factor B
- factor D
- P (properdin)
Describe the alternative pathway
Acts as a natural defense system
What protein is not stable in plasma in the alternative pathway?
C3
What has the ability to bind to factor B?
- iC3 (C3b)
What happens when C3b binds to factor B in the alternative pathway?
- factor D with magnesium can cleave B into Ba and Bb
Describe Factor D
- plasma protein that circulates in active enzyme form
- serine protease
- only substrate is bound to factor B
What occurs once B is cleaved into Ba and Bb in the alternative pathway?
1) Ba goes off into plasma
2) Bb binds to the surface of the triggering cellular antigen
3) if it does not bind quickly, it disintegrates.
What does C1 inhibitor (C1-INH) inhibit?
- activation of the first stages of the classical and lectin pathway
What is MCP also known as?
CD46
What is DAF is also known as?
CD55
What is Factor I?
- serine protease that inactivates C3b and C4b when bound to one of these regulators
What is immune adherence?
The ability of cells to bind complement-coated particles
Where are MCPs found?
- found on the cell membrane of all epithelial and endothelial cells except erythrocytes
What is the most efficient cofactor for factor I?
MCP
Describe DAF
- a membrane glycoprotein that has wide tissue distribution
- found on peripheral blood cells, endothelial cells, fibroblasts, and numerous types of epithelial cells
What does the presence of DAF on host cells protect them from?
Bystander lysis
What is bystander lysis?
- main mechanism used in discrimination of self from nonself because foreign cells do not posses this substance
What is the principle soluble regulator of alternative pathway?
Factor H
What is S protein?
- soluble control of protein that acts at a deeper level of complement activation
- terminal pathway
What does Factor H do in the alternative pathway?
- acts by binding to C3b to prevent binding of Factor B
