MHC and antigens

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35 Terms

1
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What is an antigen?

A substance capable of stimulating an immune response by activating lymphocytes.

2
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What is an epitope?

The specific part of an antigen that binds to immune receptors (antigenic determinant).

3
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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.

4
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What are the two main types of antigens?

Foreign antigens and autoantigens.

5
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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.

6
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What are endogenous antigens?

Antigens produced within host cells (e.g., viral or self-proteins) presented via MHC I to CD8+ T cells.

7
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Define antigenicity.

The ability of an antigen to bind specifically to T-cell or B-cell receptors.

8
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Define immunogenicity.

The ability of an antigen to provoke an immune response.

9
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List factors that affect immunogenicity.

Foreignness, size, stability, complexity, genetics of the recipient, route of administration, and dose of antigen.

10
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What is a hapten?

A small molecule that has antigenicity but not immunogenicity unless bound to a larger carrier molecule.

11
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Give an example of a hapten reaction.

Penicillin can bind to albumin, forming a penicilloyl-albumin complex that causes allergic reactions.

12
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What is a cross-reaction?

When antibodies against one antigen also react with structurally similar but different antigens.

13
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What does MHC stand for?

Major Histocompatibility Complex.

14
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What is the role of MHC molecules?

To present antigenic peptides to T cells and mediate self/non-self recognition.

15
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Who discovered MHC?

George D. Snell, awarded the 1980 Nobel Prize in Physiology or Medicine.

16
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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).

17
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Which cell types recognize MHC I and II molecules?

CD8+ T cells recognize MHC I; CD4+ T cells recognize MHC II.

18
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What are the three classes of MHC molecules?

MHC I, MHC II, and MHC III.

19
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What is the main function of MHC I molecules?

Present endogenous peptides (8–10 amino acids) to CD8+ T cells.

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What is the main function of MHC II molecules?

Present exogenous peptides (13–25 amino acids) to CD4+ T cells.

21
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What is the main function of MHC III molecules?

Encode proteins involved in immune responses such as complement components and cytokines.

22
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What are the components of an MHC I molecule?

A heavy α-chain (α1, α2, α3 domains) and β2-microglobulin.

23
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What are the components of an MHC II molecule?

An α-chain (α1, α2) and a β-chain (β1, β2).

24
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What domains form the peptide-binding site in MHC I?

α1 and α2 domains.

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What domains form the peptide-binding site in MHC II?

α1 and β1 domains.

26
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Which domain binds CD8 in MHC I?

The α3 domain.

27
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Which domains bind CD4 in MHC II?

The α2 and β2 domains.

28
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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).

29
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What does polymorphism mean in the context of MHC?

Each MHC gene has multiple alleles within a population, contributing to diversity.

30
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What is an MHC haplotype?

The combination of MHC alleles inherited together on one chromosome.

31
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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.

32
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Why is MHC diversity limited within an individual?

Too many variants increase the risk of autoimmunity while too few reduce pathogen recognition.

33
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What is the relationship between MHC alleles and disease?

Certain MHC alleles can be associated with susceptibility or resistance to diseases.

34
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Which MHC alleles are associated with human diseases?

HLA-B27 (ankylosing spondylitis, Reiter’s syndrome), HLA-DR4/DQ*8 (type 1 diabetes).

35
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Which canine MHC allele is linked to anal furunculosis?

DLA-DRB1*00101 increases risk with an odds ratio of 5.01.