Section IV: Adaptive Immunity Flashcards
What is specificity
- recognition of foreign substances
- a small molecule called hapten can also act as an antigen, but only when bound to a larger molecule
What are the characteristics of adaptive immunity
- specificity
- self recognition
- memory
What is memory
following the first exposure to antigen, immune system develops memory to provide rapid secondary response to same antigen
What is the bodies two part strategy for eliminating foreign material
- humoral response
- cell mediated response
What is a humoral response
eliminates antigens that are extracellular, for example bacteria in the bloodstream
What is a cell mediated response
deals with antigens residing within a host cell, for example a virus infected cell
What is the structure of an antigen
large carrier molecule with epitopes projecting from surface. Epitopes interact with antibody and T cells
What are the origins of exogenous antigens
those that have entered the body from the outside, for example by inhalation, ingestion, or injection
What are the origins of endogenous antigens
those that have been generated within the cell, as a result of normal cell metabolism, or because of viral or intracellular bacterial infection
What are superantigens
- do not behave as normal antigens. Rather than attaching to the MHC groove and triggering a normal immune response, superantigens attach onto the sides of the binding site
- as a result, T cells go on an unregulated rampage, uncontrollably releasing regulatory molecules-such as interferons- in toxic amounts
What are Class I MHC’s
- presents proteins (antigens) from inside cell
- also presents abnormal proteins on surface of virus infected cells or tumor cells for inspection by cytotoxic T cells
- cytotoxic T cells will destroy “non-self” proteins
What are Class II MHC
presents antigens from outside cell
-MHC II proteins display non-self which will be recognized by helper T cells
Where are MHC II proteins found
ONLY on immune cells called antigen presenting cells
What are activated dendritic cells
Found in those tissues which are in contact with the environment: in the skin and lining of nose, lungs, stomach, and intestines
What are activated macrophages
- present antigen early in infection
- the presence of the antigen activates macrophages
- activated macrophage processes the antigenic material
What happens following processing by an activated macrophage
- epitopes from the antigen are presented on the macrophage surface in combination with MHC proteins
- presented antigen is the recognized by helper T cells
- recognition activates the helper T cells
What do activated helper T cells regulate
Cell mediated and Humoral immunity
Does a T cell produce antibodies
no… never… never ever
Do T cells interact with free antigens
no.
- anitgen must be presented to T cell by another cell (CD4 cell)
Where are inactive (naive) T cells located
- restricted to circulation
- cannot migrate into tissues
What is required for activation of T cells
- must encounter antigen presented on cell in antigen-MHC complex
- must also be concurrently stimulated by other molecules
What does activation of T cells lead to
- formation of specific effector cells types
- effector T cells have different roles in cell mediated immunity
What are functions of activated T cells
- proliferative, develop into different effector cells
- bring antigens to naive T cells
- Release lymphokines which act as messengers, they do not respond to specific antigen, instead lymphokines act to recruit other cell types, particularly macrophages
What are CD4 T lymphocytes and what is there roll
- T cells that carry the CD4 marker can be T helper cells
- The role of T helper cells is to judge the significance of antigen presented by APC’s
What happens following recognition by T helper cells
B cells development stimulated and other T cells by releasing cytokines
–impacts both cell mediated and humoral immunity
What are Th1 cells
- judge antigen presented by macrophages. If a Th1 cell recognizes the antigen it responds by activating the macrophage
- Th1 cells orchestrate the cell mediated response by releasing lymphokines to stimulate proliferation of T cells, stimulate natural killer cells and recruit macrophages
What are Th2 cells
- judge antigen presented by B cells
- if Th2 cell recognizes the antigen it responds by activating the B cell to produce antibody
- Th2 cells also stimulate proliferation of B cells
What are T regulatory cells
also carry CD4 marker
-block induction and activity of T helper cells and B cells
What are CD8 T lymphocytes
Most T cells have the CD8 marker
- T cytotoxic cells induce apoptosis in self cells infected with virus or other microbe. Can also destroy cancerous cells
- > T cytotoxic cells recognize dysfunctional self cells by recognition of antigen presented on MHC I molecules
What are T memory cells
long lived anitgen activated T cells that respond with heightened reactivity to secondary exposure with specific antigen
How is Type IV hypersensitivity immune response mediated and how does it occur
mediated by cellular immunity
-occurs when effector T cells regulate delayed allergic reactions
What happens when CD4 and CD8 are out of balance
compromised cellular immunity
What do lymphokines activate
activation of macrophages
- activation of polymorphonuclear leukocytes
- activation of lymphocytes
- other lymphokines
What is macrophage activation factor (MAF)
activates macrophages and allows them to act as cytotoxic cells that non-specifically kill tumor cells
What is Macrophage migration inhibitory factor (MIF)
- Inhibits random migration of macrophages, role in T cell activation
- MIF is now recognized as a principle cytokine modulating T cell/macrophage interactions in the expression of delayed hypersensitivity and acquired cellular immunity
What are chemotactic factors
substances possessing chemotactic activity
What is leukocyte inhibitory factor
inhibits the random and directed migration of polymorphonuclear leukocytes
What is eosinophil stimulation factor
stimulates eosinophil migration and is produced by mitogen or specific Ag stimulation of spleen cells fro mice infected with Schistosoma mansoni
What are interleukins
structurally and functionally distinct soluble proteins secreted by different types of leukocytes that are involved in cell to cell communication
What are cytotoxic factors
term for a factor or an agent that has a specific destructive effect on cells
What is growth inhibitory factor
found in normal human brain tissue and is expressed exclusively in the nervous system. GIF inhibits survival and the outgrowth of neurites in cortical neurons.
-Drastically reduced concentrations of this factors are found in the brains of patients with Alzheimer’s disease
What is osteoblastic factor
stimulates the formation of osteoblast cells in bone
What is collagen production
factors stimulating formation of collagen
What are interferons
proteins that elicit a virus non-specific antiviral activity. Also posses anti-proliferative and immunomodulating activities and influence the metabolism, growth and differentiation of cells in many different ways
What is Transforming growth factor
- TGFs were identified initially as proteins secreted by virus-transformed mouse cells
- TGF-beta is the most potent known growth inhibitor for normal and transformed epithelial cells, endothelial cells, fibroblasts, neuronal cells, lymphoid cells and other hematopoietic cell types
What does TGF-beta inhibit
proliferation of T lymphocytes
-shuts down clonal expansion
What mediates Humoral immunity
B lymphocytes
What do B-cells do in response to antigens
proliferate and then differentiate into plasma cells which function to produce antibodies
What are the characteristics of antibodies
- produced by plasma cells
- antibodies are found in blood serum
- antibodies also found on the surface of B lymphocytes
Why are there antibodies found on B cells
allows B cell to interact with specific antigens
- antigen interaction causes the B cell to differentiate into plasma cells and into memory cells important concept
- allows plasma cells to to produce free antibody
What is the role of antibodies
- agglutination
- precipitation
What recognizes antigen/antibody complexes
phagocytic cells
What is an antitoxin
antibody with the ability to neutralize a specific toxin
What is an opsonin
any molecule that acts as a binding enhancer for the process of phagocytosis
-antibodies can be opsonins
opsonin~helper
What is the basic structure of an antibody
consist of two high molecular weight polypeptide chains called heavy chains and two lower molecular weight polypeptide chains called light chains
What type of bond holds the chains together
disulfide bonds
What is the Fab- fragment
binding portion, binds the antigen
What is the Fc- fragment
crystalline fragment, determines the antibody class
Where is the variable region found on the antibody
at the end of the Fab region
What is the constant region
encompasses the entire Fc region as well as one domain of both heavy and light chains in the Fab region
What is IgG
- monomer
- most abundant immunoglobulin
- agglutinates and precipitates antigen, also can act as antitoxin
- When multiple bind to surface of antigen a specific complement protein binds to FC region to begin complement cascade
- crosses placental barrier to provide passive immunity to fetus
What is IgM
- pentamer
- Largest immunoglobulin, large size prevents from entering tissue
- first class to be produced in response to antigen
- most efficient class at activating complement cascade
What is IgA
- pentamer
- found in body secretions
- exists as monomer in blood, but secreted as dimer
What is IgE
- monomer
- barely detectable in normal blood, most bound via Fc region to mast cells ad basophils
- involved in allergy, triggers release of histamines by binding mast cell
- can cause anaphylactic shock
What is IgD
- Monomer
- found in low levels in serum, role is uncertain
- primarily found on B cells surfaces where it function as a receptor for antigen
- does not bind complement
What is the complement system
series of proteins that constantly circulate in blood and tissue fluid
-augment, or complement the activities of antibodies
What are the characteristics of complements
- complement proteins are always circulating and can be quickly activated
- when activated various complement proteins attach to cell surfaces-forms membrane attack complex
- complement binding prepares cell for phagocytosis
- complement binding can release active substances
- complement binding can lyse cell
What is the classical complement cascade
antibody binding to antigen is necessary for cascade
- C1 binds to Fc portion of antibody
- C1 converted to enzyme which splits into C2 and C3
- C3 splits to C3a and b
- C3b combines with C4b2b to create C5 convertase
What is the alternative complement pathway
- bypasses portion of classical system b/c no antibody/antigen binding is required
- involves 4 proteins, factors B and D, properdin, and C3
- activated by:
- > plant, fungal, bacterial polysaccharides
- > bacterial lipopolysaccharides
What are the functions of complements
- formation of membrane attack complex (MAC) that causes cell lysis, especially true when bacteria is antigen
- complement proteins mark antigens and attract phagocytic cells
- complement proteins can act as opsonins
- complement proteins can act as anaphylatoxins leading to anaphylaxis
What can occur if complement is not controlled
vascular damage and initiation of coagulation
-following initiation of coagulation, components of coagulation are consumed and destroyed, results in hemorrhage
What is the primary immune response
- the first response to a particular antigen
- the adaptive immune system requires 1 week or more to respond
- first antibody produced during adaptive immune response is IgM then IgG
Whatis an T cell independent antigen
do not require presentation, rather B cells respond directly to antigen
What is a T cell dependent antigen
require presentation to helper T cell
What is the secondary immune response
- memory cells are stimulated consequently the adaptive immune response occurs only after a short delay
- level of IgG is higher and longer lasting
- less antigen needed to elicit response of immune system
- memory may persist for years
