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What is an antigen?
A substance capable of stimulating an immune response by activating lymphocytes.
What is an epitope?
The specific part of an antigen that binds to immune receptors (antigenic determinant).
How do B-cell epitopes differ from T-cell epitopes?
B-cell epitopes are surface structures recognized directly by BCRs, while T-cell epitopes are processed peptides presented with MHC molecules.
What are the two main types of antigens?
Foreign antigens and autoantigens.
What are exogenous antigens?
Antigens from outside the body that are processed by antigen-presenting cells and presented via MHC II to CD4+ T cells.
What are endogenous antigens?
Antigens produced within host cells (e.g., viral or self-proteins) presented via MHC I to CD8+ T cells.
Define antigenicity.
The ability of an antigen to bind specifically to T-cell or B-cell receptors.
Define immunogenicity.
The ability of an antigen to provoke an immune response.
List factors that affect immunogenicity.
Foreignness, size, stability, complexity, genetics of the recipient, route of administration, and dose of antigen.
What is a hapten?
A small molecule that has antigenicity but not immunogenicity unless bound to a larger carrier molecule.
Give an example of a hapten reaction.
Penicillin can bind to albumin, forming a penicilloyl-albumin complex that causes allergic reactions.
What is a cross-reaction?
When antibodies against one antigen also react with structurally similar but different antigens.
What does MHC stand for?
Major Histocompatibility Complex.
What is the role of MHC molecules?
To present antigenic peptides to T cells and mediate self/non-self recognition.
Who discovered MHC?
George D. Snell, awarded the 1980 Nobel Prize in Physiology or Medicine.
What is the difference between syngeneic and allogeneic tissue transplants?
Syngeneic transplants are between genetically identical individuals (not rejected), allogeneic are between genetically different ones (rejected).
Which cell types recognize MHC I and II molecules?
CD8+ T cells recognize MHC I; CD4+ T cells recognize MHC II.
What are the three classes of MHC molecules?
MHC I, MHC II, and MHC III.
What is the main function of MHC I molecules?
Present endogenous peptides (8–10 amino acids) to CD8+ T cells.
What is the main function of MHC II molecules?
Present exogenous peptides (13–25 amino acids) to CD4+ T cells.
What is the main function of MHC III molecules?
Encode proteins involved in immune responses such as complement components and cytokines.
What are the components of an MHC I molecule?
A heavy α-chain (α1, α2, α3 domains) and β2-microglobulin.
What are the components of an MHC II molecule?
An α-chain (α1, α2) and a β-chain (β1, β2).
What domains form the peptide-binding site in MHC I?
α1 and α2 domains.
What domains form the peptide-binding site in MHC II?
α1 and β1 domains.
Which domain binds CD8 in MHC I?
The α3 domain.
Which domains bind CD4 in MHC II?
The α2 and β2 domains.
What does polygeny mean in the context of MHC?
MHC has multiple genes encoding different MHC molecules (e.g., HLA-A, HLA-B, HLA-C).
What does polymorphism mean in the context of MHC?
Each MHC gene has multiple alleles within a population, contributing to diversity.
What is an MHC haplotype?
The combination of MHC alleles inherited together on one chromosome.
How many different MHC molecules does a human typically express?
Six class I (A, B, C) and six class II (DQ, DP, DR) = about 12 total MHC molecules.
Why is MHC diversity limited within an individual?
Too many variants increase the risk of autoimmunity while too few reduce pathogen recognition.
What is the relationship between MHC alleles and disease?
Certain MHC alleles can be associated with susceptibility or resistance to diseases.
Which MHC alleles are associated with human diseases?
HLA-B27 (ankylosing spondylitis, Reiter’s syndrome), HLA-DR4/DQ*8 (type 1 diabetes).
Which canine MHC allele is linked to anal furunculosis?
DLA-DRB1*00101 increases risk with an odds ratio of 5.01.