Exam 3 - MHC Complex (AI Flashcards)
What is the Major Histocompatibility Complex (MHC)?
An extended genetic locus that contains several highly polymorphic genes that encode highly polymorphic cell surface proteins.
The MHC is crucial for the immune system, particularly in recognizing foreign antigens.
What is polymorphism in the context of MHC?
The presence of multiple alleles at a gene locus within a population.
Each common variant of a polymorphic gene is called an allele.
What does it mean to be homozygous for an allele?
Having the same allele on each of the two chromosomes.
Conversely, being heterozygous means having two different alleles.
What are syngeneic mice?
Inbred sibling mice that are genetically identical and will accept each other’s tissue grafts.
This occurs after ~20 generations of inbreeding.
What are allogeneic mice?
Different inbred strains that will not accept tissue grafts from another inbred strain.
Who discovered the MHC and its relation to transplantation immunology?
George Snell (1903-1996)
What is the primary function of MHC molecules?
To present antigen epitopes to T cell receptors (TCRs).
MHC molecules are recognized together with epitopes by the TCR.
What are the two classes of MHC molecules?
MHC Class I and MHC Class II.
What type of T cells do MHC Class I molecules present epitopes to?
CD8+ T cells.
Where are MHC Class I molecules expressed?
On all nucleated cells in the body.
They are not expressed on red blood cells (RBCs).
What type of T cells do MHC Class II molecules present epitopes to?
CD4+ T cells.
Where are MHC Class II molecules primarily expressed?
On antigen-presenting cells (APCs): macrophages, dendritic cells, and B cells.
What is the structure of MHC Class I molecules?
Consists of a heavy chain and a light chain (beta-2 microglobulin).
What is the structure of MHC Class II molecules?
Consists of an alpha chain and a beta chain.
What is unique about the peptide-binding cleft of MHC Class I?
It is closed at the ends, forming a pocket for the antigen peptide.
What is unique about the peptide-binding cleft of MHC Class II?
It is open at the ends, allowing the peptide to hang outside of the cleft.
What is the typical peptide length that MHC Class I can bind?
8-10 amino acids in length.
What is the typical peptide length that MHC Class II can bind?
13-17 amino acids in length (can be >30).
What determines the specificity of peptide binding to MHC molecules?
The T cell receptor (TCR) determines the specificity.
MHC molecules have a broad specificity for peptide binding.
What types of peptides do MHC Class I molecules present?
Cytosolic peptides.
What types of peptides do MHC Class II molecules present?
Extracellular peptides.
How is the expression of Class II MHC molecules regulated?
Their expression is usually regulated and can be up-regulated by cytokines during immune responses.
What effect does IFN-g have on MHC expression?
It increases MHC expression and antigen presentation.
