(DSA8) Antigens and Antibodies Flashcards
Differentaite between antigens, immunogens, and tolerogens.
DSA8(Ag) S4
Antigen:
-a molecule or protion of a molecule that is recognized by the immune system
Immunogen:
-Ag that generates and immune response
Tolerogen:
-Ag that induces immunologic tolerance
Differentiate between endogenous and exogenous Ags.
DSA8(Ag) S5
Endogenous:
-antigens generated by the body or intracellular pathogens
Exogenous:
-outside antigens that have entered the the body
What are epitopes and what are the types of determinents?
DSA8(Ag) S6
Portion of an Ag that binds with Abs, BCRs, or TCRs
Conformational determinant:
- epitope found only on antigen when in native conformation
- denaturing results in loss of epitope
Liner determinant:
- epitope consists of continuous portion of Ag
- epitope may or may not be exposed in native conformation
Neoantigenic determinant:
-epitope generated only following selective proteolysis
What is the difference between T-dependent Ags and T-independent Ags?
DSA8 (Ag) S7
T-dependent:
- requires Th2 costimulation to illicit Ab prodution and isotype switching
- protein Ag
- produces IgG, IgA, and IgE
T-independent:
- does not require Th2 constimulation to illict Ab produciton; no isotype switching
- multivalent lipid, polysaccharide, and nucleic acid Ags
- produces IgM
What types of epitopes are recognized by T lymphocytes?
DSA8(Ag) S8
The linear epitope of proteins are the m Ags recognized by TCRs.
Ags must be presented by APCs as TCRs do not bind free peptides.
What is special about γδ T cells when compared to αβ T cells?
DSA8(Ag) S9
Located in epithelial/mucosal compartments (oral, respiratory, vaginal, anal, etc.)
Can bind non-protein Ags and DAMPs
Do not require MHC presentation
Comprise 5-10% of T cell population
What are haptens and why are they significant?
DSA8 (Ag) S11
Haptens are too small to be to illict an immune response on their own.
They must be coupled with a carrier protein to create a response.
Most drug allergies occur via this mechanism and vaccines are designed this way.
What are super antigens and what is their mechanism?
DSA8(Ag) S13
Binds outside of MHC groove and to certain β chains of TCRs. This overly activates the affected T cells and affects more T cells as it does so regardless of the specificity of the T cell.
Super antigens are responsibel for:
- food poisoning (enterotoxins)
- toxic shock syndrome (toxic shock toxin)
- scalded skin syndrome (exfoliating toxin)
- shock (pyrogenic exotoxins)
Differentiate between antibodies and BCRs.
DSA8(Ab) S5
Antibody:
- soluble
- effector mechanisms through Fc portion of tail which binds Fc receptors (opsonization, NK cell activation, mast cell activation, complement activation)
- effector mechanisms also through Ag binding (neutralization)
BCR:
- membrane bound to B cells
- intracellular signaling domain (ITAMs)
What is the structure of an antibody and what is the function of each region?
DSA8(Ab) S6
Heavy chain:
-variable, Ag binding region (VH)
-constant, biologically active region (CH and hinge)
Light chain:
- variable, Ag binding region (VL)
- constant region (CL)
What is the results of digestion of an antibody with papain or pepsin?
DSA8(Ab) S7
Papain:
-digested into two seperate Fab regions and an intact Fc region
Pepsin:
-digested into two connected Fab regions and degraded Fc region
What is the hypervariable region of an antibody and what is its funciton?
DSA8(Ab) S8
Three regions found in the V domain surrounded by framework regions.
The hypervariable regions create a charge and shape complimentarity to the antigen they are specific for.
What is the difference between allotypes and idiotypes?
DSA8(Ab) S10
Allotype:
-genetic variations of the constant regions
Idiotypes:
-genetic variations of the variable regions
What is the structure of IgM?
What role does it play in immune response?
DSA8(Ab) S12
Structure:
- pentamer with 10 Ag-binding sites
- J-chain (required for transport into mucosa)
- 4 heavy chain constant regions
Function:
- predominantly produced in primary responses (first exposure)
- coexpressed on mature B-cells with IgD
- only Ab produced by fetus (late)
What is the structure of IgG?
What role does it play in immune response?
DSA8(Ab) S13
Structure:
- monomer
- 3 heavy chain constant regions
Function:
- predominantly produced in secondary responses (any exopsure after first)
- only Ab to cross placenta (passive immunity to fetus and neonate)
What is the structure of IgA?
What role does it play in immune response?
DSA8(Ab) S14
Structure:
- monomer (serum) and dimer (mucosa)
- J-chain (required for transport into mucosa)
- secretory component (portion of receptor from transport)
- 3 heavy chain constant regions
Function:
- component of secondary immune response
- predominantly found in secretions (colostrum, saliva, tears, and mucus)
- provides passive immunity to newborns via breast milk
What is the structure of IgE?
What role does it play in immune response?
DSA8(Ab) S15
Structure:
- monomer
- 4 heavy chain constant regions
Function:
- component of secondary immune response
- activates basophils and mast cells
- protection against helminth (parasitic worms) infeciton
function in allergic/asthmatic responses
What is the structure of IgD?
What role does it play in immune response?
DSA8(Ab) S16
Structure:
- monomer
- 3 heavy chain constant regions
Function:
- coexpressed on mature B-cells with IgD
- minimal serum pressence
What is the function of FcγRI (CD64), where is it located, and what antibody is it specific for?
DSA8(Ab) S18
Binds IgG1 and 3 with high affinity
Located on phagocytes
Triggers phagocytosis of IgG opsonized targets
What is the function of FcγRIIA (CD32), where is it located, and what antibody is it specific for?
DSA8(Ab) S18
Binds IgG with low affinity
Found on phagocytes and eosinophils
Triggers phagocytosis or degranulation
What is the function of FcγRIIB (CD32), where is it located, and what antibody is it specific for?
DSA8(Ab) S18
Binds IgG with low affinity
Located on B cells, phagocytes, and mast cells
Provides feedback inhibition to B-cells and inhibits cell activity
What is the function of FcγRIIIA (CD16), where is it located, and what antibody is it specific for?
DSA8(Ab) S18
Binds IgG with low affinity
Found on NK cells (CD16+ cells)
Triggers antibody dependent cellular cytotoxicity (ADCC), effector mechanism of NK cells
What is the function of FcεRI (CD32), where is it located, and what antibody is it specific for?
DSA8(Ab) S18
Binds IgE with high affinity
Found on mast cells, basophils, and eosinophils
Triggers degranulation
How do the terms affinity, valence, and avidity relate?
DSA8(Ab) S21
Affinity is the strength of interaction between the Ag epitope and Ab paratope (affinity of IgG is higher than affinity of IgM).
Valence refers to how many Fab regions an Ab has (valence of IgG is 2 and IgM is 10).
Avidity is the overall strength of an Ab-Ag complex and it is directly related to both affinity and valence.
What is isotype switching?
DSA8(Ab) S22
DNA splicing to exchange μ-heavy chain for IgM out with α, ε, or γ-heavy chains to produce IgA, IgE, and IgG respectively.
T-dependent
What is affinity maturation?
DSA8(Ab) S22
Mutations that occurs in B-cells that are activated by folicular T helper cells (T-dependent response)
Process involves somatic hypermutation and clonal selection
Does not occur to IgM as it is T-independent but does occur in IgG, IgA, and IgE as they are T-dependent
