4: Major histocompatibility complex

Question 1

main purpose of MHC

Answer 1

encodes molecules used to present processed antigens to T cells

Question 2

3 types of epitopes recognized by MHC

Answer 2

• polygenic (several genes exist for a given MHC class)
• polymorphic (a large number of alleles exist for a given gene)
• promiscuous (will bind a range of similar epitopes)

Question 3

MHC class I

Answer 3

• encodes a single chain

- presents endogenous antigens to CD8+ t cells (cytotoxic t cells)

Question 4

MHC class II

Answer 4

• encodes 2 chains (alpha and beta)

- presents exogenous antigens to CD4+ t cells (helper t cells)

Question 5

MHC class III

Answer 5

encodes cytokines, heat shock proteins, antigen processing and transport proteins, and complement proteins

Question 6

class I and II v class III MHC

Answer 6

• class I and II physically present the antigen on the surface of a cell
• class III is a loose term for all other genes in the MHC region

Question 7

what is MHC class I recognition especially important for

Answer 7

virus-infected cells

Question 8

where are MHC class I expressed

Answer 8

on the surface of all nucleated cells

Question 9

where are MHC class II expressed

Answer 9

predominantly on immunocytes

Question 10

what is MHC II important for

Answer 10

activation of t helper cells for inducing the immune response

Question 11

does MHC have high or low rate of mutation among populations

Answer 11

high

Question 12

what type of expression does MHC class II have

Answer 12

codominant expression

Question 13

how is MHC able to present a wide variety of processed peptides

Answer 13

has several loci which code for molecules of the same function and by has many allenes within the population

Question 14

MHC and diseases

Answer 14

linkage of MHC alleles with specific disease susceptibility traits or autoimmune pathologies

Question 15

heritability of MHC allels

Answer 15

high number of alleles assures that most individuals are heterozygous at each of the MHC loci

Question 16

steps in antigen processing (4)

Answer 16

• internalization of antigen into APC
• antigen processing
• processing generates multiple peptides, one of which can bind to class II allele
• t cells respond to immunodependent peptide epitope

Question 17

what does APC mean

Answer 17

antigen presenting cells (display processed antigen as peptide fragments on the cell surface)

Question 18

what does MHC influence

Answer 18

whether or not antigen-specific immune responses will occur (which epitopes the immune system responds to)

Question 19

what is MHC restriction

Answer 19

a given t cell receptor will only recognize antigen presented by a particular (self) MHC molecule
-t cells educated in 1 MHC allele/epitope will not interact with APC unless it expresses that allele bearing that same epitope