Immunology MHC Molecules Quiz

Questions and Answers

Define MHC molecules?

Membrane-associated glycoprotein molecules whose function is to bind peptide antigens and present them to T cells.

Function of MHC class I molecules involves binding and transport of peptide antigens generated in the cytosol to the cell surface for recognition by ___ T cells.

CD8

What is the function of MHC class II molecules?

Binding and transport of peptide antigens generated in the endocytic vesicles to the cell surface for recognition by CD4 T cells.

MHC class I molecule consists of a transmembrane ___ chain, a-chain, which has 3 extracellular domains (a1, a2 and a3).

heavy Signup and view all the answers

The ___ domains, farthest from the membrane, form the peptide binding site.

a1 and a2 Signup and view all the answers

The MHC class I heavy chain is encoded by a gene in the MHC on chromosome ___.

6 Signup and view all the answers

There is also a covalently complexed invariant polypeptide, _ (also called the light chain of class I MHC molecule), which is on chromosome .

b2 microglobulin, 15 Signup and view all the answers

MHC class II molecule consists of two transmembrane chains; one _ and one _ chain.

a, b Signup and view all the answers

One domain from each chain, farthest from the membrane, contributes to form the peptide binding site (_ and _).

a1, b1 Signup and view all the answers

What does the a3 domain of MHC class I bind to?

CD8 co-receptor Signup and view all the answers

What does the b2 domain of MHC class II bind to?

CD4 co-receptor Signup and view all the answers

Class I is expressed on all _ cells, especially _ cells.

nucleated, hematopoietic Signup and view all the answers

What are the 6 isotypes of MHC class I molecules?

HLA-A, HLA-B, HLA-C, HLA-E, HLA-F, HLA-G Signup and view all the answers

What are HLA-E and HLA-G?

Oligomorphic and serve as ligands for NK cell receptors. Signup and view all the answers

What are the 5 isotypes of MHC class II molecules?

HLA-DP, HLA-DQ, HLA-DR, HLA-DM, HLA-DO Signup and view all the answers

What is the function of HLA-DM and HLA-DO?

Regulates peptide loading of HLA-DP, HLA-DQ and HLA-DR. Signup and view all the answers

What are 3 factors that dictate polymorphism and thus diversity?

Polymorphism, polygeny, and co-dominant expression. Signup and view all the answers

What does polygeny refer to?

The existence of multiple similar genes encoding the MHC class I heavy chains, MHC class II a chains, and MHC class II b chains. Signup and view all the answers

At the event of antigen presentation, the peptide/MHC complex is recognized by TCR. TCR binds to what?

Both the peptide and the MHC molecule. Signup and view all the answers

This restriction in antigen specificity of T cells due to MHC is called what?

MHC-restriction. Signup and view all the answers

MHC molecules bind peptides via ___ on the peptide.

"anchor residues" Signup and view all the answers

The existence of ___ expands the number of different peptides that an individual can present.

multiple genes Signup and view all the answers

Co-dominant expression maximizes what?

The number of MHC molecules expressed by an individual. Signup and view all the answers

All the alleles involved with HIV progression (or slowing) are MHC class _, which is associated with _ from cytotoxic CD8 T cells.

I, killing of virus infected Signup and view all the answers

What are the two ways of possible cross-reactive recognition in T cell alloreactivity?

Peptide dominant binding and MHC dominant binding. Signup and view all the answers

What are superantigens (SAgs)?

A distinct class of antigens that stimulate a primary T cell response after being presented as an intact protein molecule by MHC class II molecules. Signup and view all the answers

What are two examples of bacterial superantigens?

Staphylococcal enterotoxin (SE) and Toxic shock syndrome toxin (TSST). Signup and view all the answers

Superantigen binds to the _ region of TCR and to the _ of MHC class II molecule.

Vb, outer surface Signup and view all the answers

SAg induces a _ T cell response resulting in production of large amounts of _ responsible for inducing a ___

polyclonal, cytokines (IL-1, IL-2, TNF-a), systemic shock Signup and view all the answers

SAg also inhibits the induction of what?

Specific adaptive response, which favors the pathogenicity of the bacteria. Signup and view all the answers

Study Notes

MHC Molecules Overview

MHC (Major Histocompatibility Complex) molecules are membrane-associated glycoproteins that bind peptide antigens for T cell recognition.
MHC class I presents antigens to CD8 T cells, while MHC class II presents to CD4 T cells.

Functions of MHC Class I Molecules

Transport peptide antigens from the cytosol to the cell surface for CD8 T cell recognition.
Involved in IgG uptake in the gut and regulation of iron metabolism and NK cell function.

Functions of MHC Class II Molecules

Bind and transport peptide antigens from endocytic vesicles to the cell surface for recognition by CD4 T cells.

Structure of MHC Class I Molecules

Comprises a heavy chain (transmembrane α-chain) with three extracellular domains (α1, α2, α3), forming the peptide binding site.
Heavy chain encoded by MHC genes on chromosome 6, with a covalently bound light chain known as β2 microglobulin encoded on chromosome 15.

Structure of MHC Class II Molecules

Consists of two transmembrane chains: α and β, both encoded by MHC genes.
Peptide binding site formed by one domain from each chain (α1 and β1) located farthest from the membrane.

Binding and Recognition

The α3 domain of MHC class I binds to the CD8 co-receptor, ensuring presentation to CD8 T cells.
The β2 domain of MHC class II binds to the CD4 co-receptor for presentation to CD4 T cells.

Expression Patterns

MHC class I is expressed on all nucleated cells, especially hematopoietic cells; red blood cells lack MHC class I expression.
MHC class II is expressed primarily on professional antigen-presenting cells (APCs) like dendritic cells, macrophages, and B cells.

Isotypes of MHC Class I Molecules

Six isotypes: HLA-A, HLA-B, HLA-C, and HLA-G, with HLA-G being less polymorphic.
Highly polymorphic isotypes present antigens to CD8 T cells and are ligands for NK cell receptors.

Isotypes of MHC Class II Molecules

Five isotypes: HLA-DP, HLA-DQ, HLA-DR, HLA-DM, and HLA-DO.
HLA-DR is highly polymorphic and directly presents peptides to CD4 T cells.

Functions of HLA-DM and HLA-DO

HLA-DM regulates peptide loading on HLA-DP, HLA-DQ, and HLA-DR.

MHC Polymorphism and Diversity

Diversity is driven by polymorphism, polygeny (multiple similar genes), and co-dominant expression of alleles.
Co-dominant expression maximizes the number of MHC molecules an individual can express.

MHC Restriction

T cell receptors (TCRs) recognize complex peptides bound to MHC molecules, known as MHC-restriction, influencing T cell specificity.

MHC Class I and HIV Progression

Alleles related to HIV progression are associated with MHC class I molecules and their role in cytotoxic CD8 T cell activity against virus-infected cells.

T Cell Alloreactivity

Cross-reactivity of TCRs can be explained by peptide dominant and MHC dominant bindings, influencing the immune response during transplants.

Superantigens (SAgs)

Distinct antigens that stimulate T cell responses by presenting intact proteins through MHC class II, as opposed to standard peptide presentation.
Examples include Staphylococcal enterotoxin and Toxic shock syndrome toxin.

Mechanism of Superantigens

Superantigens bind the Vβ region of the TCR and the outer surface of MHC class II, inducing polyclonal T cell activation and massive cytokine production, leading to systemic shock.
They inhibit the induction of specific adaptive responses, favoring bacterial pathogenicity.

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Description

Test your knowledge on MHC molecules and their functions with this quiz. Explore the roles of MHC class I in immune responses and the presentation of antigens to T cells. Perfect for students studying immunology and related fields.