Infection and immunity Flashcards
The ability of an organism to defend itself against infectious agents, foreign cells and proteins, and catastrophic cell dysfunction (e.g. cancer)
Immunity
Name the two different types of immunodeficiency
- Genetic inheritance (e.g. Severe Combined Immune Deficiency)
- Acquired during life (e.g. AIDS)
A damaging immune response by the body to a substance, especially a particular food, pollen, fur, or dust, to which it has become hypersensitive.
Allergy
Allergy and hypersensitivity result when the immune system responds….
innappopriately to antigens.
An extreme hypersensitivity reaction where the immune system attacks its own body tissues
Auto-immunity
In autoimmune conditions, what types of cells mount an attack against the body’s own tissues?
B & T cells. This is the result when T cell control mechanisms fail.
List the three key areas of immunological disease:
- Immunodeficiency
- Auto-immunity
- Allergy
Name the two branches of the immune system
Innate and adaptive
Which branch of the immune system is the first immunological mechanism for fighting against intruding pathogens?
The innate immune response
Which of the two branches of our immune system is more immediate (initiated within minutes or hours)?
Innate
Does the innate immune system have immunologic memory?
No
Which branch of the immune system is antigen dependent and antigen specific?
The adaptive immune response
Which of the two branches of the immune system has capacity for memory?
The adaptive immune response
What is the purpose of memory in the adaptive immune response?
Memory to specific antigens enables the host to mount a more rapid and efficient immune response upon subsequent exposure to the antigen. This should prevent an infection on the second encounter.
In which part of the lymphatic system do lymphocytes and macrophages generally reside (in concentrated areas)?
Lymph nodes
Where are blood cells produced, including B and T lymphocytes?
Red bone marrow
Which organ acts as an emergency blood store?
The spleen
Where is blood cleansed of pathogens and debris?
The spleen
What is the site of maturation of T-lymphocytes?
The thymus gland
What is the name of the inital cells that give rise to all other blood cells?
Hematopoietic stem cells
What is the “parent” cell of T cells, B cells, and natural killer cells?
Lymphoid progenitor
What is the “parent” cell of dendritic cells, granulocyte-monocyte progenitors, eosinophil progenitors, basophil progenitors, erythroid progenitors, and megakaryocytes?
Myeloid progenitor
What is the job of dendritic cells?
Antigen-presenting cells
Megakaryocytes produce what kinds of cells?
Platelets
Erythroid progenitors produce what kind of cells?
Erythrocytes (red blood cells)
Which type of cell is mostly involved with host defenses against multicullular parasites?
Basophils
What type of cell is mostly involved in defense against nematodes and parasites?
Eosinophils
This type of cell coordinates the inflammatory response and is the 1st line of defense in bacterial infections
Neutrophils
These are the “scavenger” cells; phagocytic, highly migratory. Also professional antigen presentation
Macrophages
Macrophages are produced from…
Monocytes
Name the leucocytes with myeloid lineage (4)
- Basophils
- Eosinophils
- Neutrophils
- Monocytes/macrophages
Name the leucocytes with lymphoid lineage (4)
- T cells (CD8 and CD4)
- B cells
- NK cells
- Dendritic cells
What would trigger a haematopoietic stem cell to differentiate into either a myeloid progenitor cell or a lymphoid progenitor cell?
Molecular messengers such as cytokines and chemokines
Name the two different types of T cells
- T Helper cells (CD4+)
2. Cytotoxic cells (CD8+)
What type of lymphocyte produces antibodies?
B cells (plasma cells)
True or false: dendritic cells can come from either myeloid or lymphoid progenitor cells
True
These are the effector lymphocytes of the innate immune system. They are best known for killing virally infected cells, as well as for detecting and controlling early signs of cancer.
Natural killer cell
Natural killer cells are derived from what type of progenitor cell?
Lymphoid progenitor
This type of leucocyte activates B cells to secrete antibodies and macrophages. It can also activate cytotoxic T cells
T helper cell (CD4+)
This type of T cell directly kills virally infected cells and tumours
T cytotoxic cell (CD8+)
Which leucocyte is integral to the adaptive immune response?
B cells
Define “immunological memory”
The adaptive immune system exhibits a memory function that kicks in quickly if a pathogen is encountered again later on in life. It acts quickly on the second exposure, providing a robust response that ideally should prevent an infection.
This is the state of immunological non-reactivity to an antigen
Tolerance
What type of immune disorders can result from a breakdown of tolerance?
Auto-immunity or allergies
Describe how alleriges can develop
Allergies can result when there is a breakdown of tolerance, and the body reacts to potential antigens that are not actually harmful (e.g. pollen, dust).
Describe how auto-immunity can develop
Auto-immunity can result when there is a breakdown of tolerance, and the body reacts to its own tissues as if they were antigens.
What are the steps involved in antigen-antibody phagocytosis?
- Antibodies (produced by B cells) bind to specific antigens on pathogens
- Antibodies then act as a bridge between a phagocytic cell and a pathogen
- The antigen-mediated cross-linking drags Fc receptor complexes on the phagocytic cell closer together, stimulating phosphorylation to occur
- The phosphorylation results in signal transduction, which signals the phagocytic cell to engulph the pathogen
What triggers phagocytosis of a pathogen?
The Fc receptors being dragged closer together by cross-linking
Glycoproteins that have the ability to bind to a specific antigen are called
antibodies
What is a naive B cell?
A B cell that has not been exposed to an antigen
What happens to a B cell when it is exposed to an antigen?
The cell becomes either a memory B cell or a plasma cell that secretes antibodies
What is the result of a B cell receptor becoming activated by antigen cross-linking, and cytokine stimulation by T helper cells?
The membrane-bound surface antibody on a B cell promotes production of the soluble form of antibodies
What type of bonds join the light and heavy chains of an antibody?
Disulphide bonds
The grouping of different antibodies based on function
Antibody isotype
Name the 5 antibody isotypes
- IgM
- IgG
- IgA
- IgE
- IgD
Which is the most abundant internal immunoglobulin?
IgG
Which immunoglobulin protects external surfaces?
IgA
Which immunoglobulin is most efficient against bacteria?
IgM
Which immunoglobulin is involved in parasitic infections and allergic reactions?
IgE
Which immunoglobulin is mainly associated with lymphocyte receptors?
IgD
Which immunoglobulin can cross the placenta?
IgG
What is the significance of IgG antibodies being able to cross the placenta?
IgG antibodies passed from mother to fetus can provide some immune protection to the baby while its humoral immune response is still developing
Which antibody is highest in the classical complement fixation?
IgM
WHich immunoglobulin is best at binding to macrophages and polymorphs?
IgG
The property of mature B and T lymphocytes that enables them to respond to specific foreign antigens entering the body is known as
Antigen specificity
Antigen specificity requires mature T & B cells that have been…
…previously exposed to an antigen.
All members of the leucocyte family communicate using small, soluble messaging proteins known as
Cytokines and chemokines
What types of signalling do leucocytes use to communicate?
Autocrine (self) signalling
Paracrine (nearby cell) signalling
Juxtacrine (direct cell-to-cell) signalling
The type of communication that occurs when cytokindes and chemokines travel through the blood stream
Endocrine signalling
The type of signalling associated with hyperactivation of the immune system (cytokine storm)
Endocrine signalling
What is the most common signalling method utilised by leucocytes?
Paracrine signalling, where water-soluble signalling molecules travel through space and bind to a specific receptor with a lock and key mechanism that has a high affinity (tightness of binding)
A toxin or other foreign substance which induces an immune response in the body, especially the productino of antibodies
Antigen
What triggers the increase in blood flow and capillary permeability after tissue has been injured?
vasoactive and chemotactic factors
List the four key immunological events that underlie inflammation and its resolution
- Tissue damage triggers increase in blood flow and capillary permeability
- Permeable capillaries allow an influx of exudate and cells
- Phagocytes migrate to site of inflammation (chemotaxis)
- Phagocytes and antibacterial exudate destroy bacteria
Name some examples of barrier systems in immunity
Skin
Enzymes in mouth & upper alimentary canal
Low pH of stomach
Digestive enzymes of small intestine
Normal flora in large intestine
Airway and lungs have cilia, macrophages in alveoli, coughing/sneezing expels mucous
List the 5 key cells of innate immunity
Macrophage Neutrophil Eosinophil Basophil Dendritic cell
This type of cell is phagocytic, highly migratory; professional antigen presentation
Macrophage
This cell is highly abundant and migratory; coordinates inflammatory response
Neutrophil
This cell is involved in the host defense against nematodes and other parasites
Eosinophil
This type of cell is invloved in host defenses against multicellular parasites
Basophil
This type of cell is the most adept of the family of antigen-presenting cells
Dendritic cells
This branch of the immune system consists of physical, chemical, and cellular defenses against pathogens
Innate (or non-specific) immune response
What is the main purpose of the innate immune response?
To immediately prevent the spread and movement of foreign pathogens throughout the body
Pattern recognition receptors are associated with which branch of the immune system?
Innate
This type of receptor, on phagocytic cells, detects antigen non-specifically using receptors for PAMPS
Pattern recognition receptors
What does “PAMPS” stand for?
Pathogen
Associated
Molecular
Patterns
What types of organisms contain PAMPS?
Lower organisms (as opposed to human cells)
Name two examples of PAMPS
- Lipopolysaccharide (from the outer membrane of gram negative bacteria)
- Peptidoglycan (found in gram positive cell walls)
Pseudopodia form a __________ in the process of engulphing a pathogen.
phagosome
Which type of receptor binds to a potentially infinite array of pathogen-associated peptides- adaptive immune response receptors, or pattern recognition receptors?
Adaptive response receptors. Pattern recognition receptors bind to a limited array of PAMPS
In the adaptive response receptor of T cells, the antigens are always
Protein peptides
True or false: Pattern recogntion receptors exhibit molecular memory and ability to improve/adapt during immune response
False. This describes the ability of adaptive response receptors
The family of plasma proteins that activate each other are known as
The complement cascade
What are the main effects of the complement cascade?(3)
- Destabilises bacterial membrane
- Coats bacteria, marking them for destruction
- Attracts phagocytes to the site of infection
The complement system enhances immunity by increasing availability of ________ to the adaptive immune system.
antigen
Name a few of the soluble mediators that play a role in innate immunity
- Complement
- Lysozyme
- Cytokines
A hydrolytic enzyme present in saliva and tears that can destroy the cell wall of bacteria
Lysozyme
What are the substances that attract leucocytes to the site of infection?
Cytokines or chemokines
Molecular messengers that are capable of coordinating an immune response
Cytokines/chemokines
This is the name for a type of glycoprotein that interferes with viral replication (a cytokine)
Interferon
This refers to a type of gene rearrangement by which cells of the adaptive immune system physically cut out small regions of DNA and then paste the remaining pieces of DNA back together in an error-prone way. This process is known as
Somatic recombination
What is the benefit of somatic recombination?
It contributes to antibody diversity
Name the four gene segments of the heavy chain in an antibody
Variable (v)
Diversity (d)
Joining (j)
Constant (c)
Name the three gene segments of the light chain in an antibody
(remember- “light hain”)
Variable (v)
Diversity (d)
Joining (j)
What is the downside to somatic recombination?
Can cause genetic instability –> leukemias
List two effects of an antigen binding to a B cell receptor
- Cell is triggered to divide further, producing soluble form of antibodies
- IgM antibody matures into IgG
This process invloves minor changes in the amino acid sequence of the variable domain in the mature B cell once it encounters antigen for the first time, which can change the affinity of the antibody. This generally results in increased affinity.
Affinity maturation
What are the first isotypes of immunoglobulins produced by the B cells in the primary immune response (first phase)?
IgM and IgD
When an IgM matures into an IgG, this is known as
class switching
Class switching affects which domain of the antibody?
The constant (Fc) domain. Therefore, the Ab retains affinity for the same antigen, but can interact with different effector molecules.
What is the main isotype of antibody in the primary stage of the immune response?
IgM
What is the main isotype of antibody in the secondary stage of the immune response?
IgG
Out of the primary and secondary stages of the immune response, which is considered to be the most “robust” and effective in terms of responding to the pathogen?
The secondary response
What is the time of peak response in the primary phase of the immune response?
7-10 days
What is the time of peak response in the secondary immune response?
3-5 days
What type of B cell responds to the pathogen in the primary immune response?
A naive B cell
What type of B cell responds to the pathogen in the secondary immune response?
A memory B cell
Is antibody affinity higher in the primary immune response, or the secondary immune response?
Secondary
Describe the lineage and maturation of CD4 and CD8 T cells
- T cells originate from haematopoietic stem cells (which are produced in the bone marrow)
- Molecular messengers (cytokines or chemokines) trigger the haematopoietic stem cell to differentiate into a lymphoid progenitor cell
- Lymphoid progenitor cells travel via the blood to the thymus gland
- Cells mature in the thymus gland and become T cells
- Each T cell develops its own T cell receptor that is specific for a particular antigen
- Mature T cells leave the thymus and circulate through the lymphatic system, ready to encounter a specific antigen and become activated
CD8+ T cells recognise peptides presented by which class of molecule
MHC class I
MHC class I molecules are associated with what type of T cells?
CD8+
What is the main role of the CD4 and CD8 cells in recognising antigens?
Double checking the identity of the presenting cell before it becomes activated to either kill the pathogen or secrete cytokines that promote immune responses to kill the invading pathogen
Is the class II MHC pathway endogenous or exogenous?
Exogenous (extracellular infections)
Is the class I MHC pathway endogenous or exogenous?
Endogenous (intracellular infections, such as viruses)
Name the three types of immune cells that are capable of class II MHC presentation
Dendritic cells
Macrophages
B cells
What type of infection would result in the stimulation of the class I MHC antigen processing pathway?
A viral infection
What types of cells are capable of expressing class I MHC molecules?
All nucleated cells
The vast majority of peptides presented in Class I context are _____________ and therefore will not trigger an immune response
self-derived
MHC class I molecules are associated with what type of T cells?
CD4+
These cells recognise peptides derived from processed antigen and presented to them by another cell
T cells
These cells recognise intact protein antigen- soluble or pathogen-associated
B cells
Which type of cell has antibody receptors both on the cell surface, and in a secretory form?
B cells
Which of the lymphoid cells have major subset differentiation?
T cells (CD4+ and CD8+)
Which type of lymphoid cells mutate their receptor duing affinity maturation?
B cells
Does affinity maturation take place in T cells?
No
A failure in which branch of the immune system (in discriminating against self vs non-self tissues) could result in autoimmunity?
Adaptive
What are the three major types of cells invovled in teh adaptive immune response?
B cells, T cells, and antigen-presenting cells
What types of cells are phagocytes?
Macrophages/monocytes, and neutrophils
What are the major cell types associated with innate immunity?
Phagocytes (monocytes/macrophages, neutrophils), NK cells, and dendritic cells
Name a few acute phase proteins associated with the innate immune system
CRP, interferon, and cytokines
What are the soluble factors of the innate immune system?
Lysozyme, complement, and acute phase proteins (CRP, interferon, cytokines)
What are the soluble factors mainly associated with the adaptive immune response?
Antibodies
Which branch of the immune response has antigen specificity?
Adaptive
What are the effector T cells?
Cd4+ T helper cells and CD8+ cytotoxic cells
What happens to T cells upon reexposure to an antigen they have been previously sensitized to?
Memory T cells are quickly convereted into large numbers of effector T cells (CD4+ and CD8+) upon reexposure to the apecific antigen, thus providing a rapid resposne to infection.
