Major Histocompatibility Complex

Question 1

how is antigen recognition mediated on B cells

Answer 1

surface immunoglobulin (BCR) binds to native/unprocessed antigens on pathogens

Question 2

how is antigen recognition mediated on T cells

Answer 2

T cells only recognise parts of antigens that are processed and expressed on host cell surfaces by specialised glycoproteins known as a major histocompatibility complex (MHC)

Question 3

what are MHC molecules also referred to as in humans

Answer 3

human leukocyte antigens (HLA)

Question 4

MHC proteins are encoded in a large cluster of genes on which chromosome?

Answer 4

6

Question 5

what do T cells recognise

Answer 5

the combination of the MHC molecule and small peptide fragment of antigen
will not recognise the same peptide on a different MHC or vice versa

Question 6

the two MHC families and their 3 members

Answer 6

MHC class I: HLA-A, HLA-B, HLA-C
MHC class II: HLA-DP, HLA-DQ, HLA-DR

Question 7

which cells express either class of MHC

Answer 7

Class I: expressed on all nucleated cells including leukocytes
Class II: expressed only on leukocytes which present antigen to T cells i.e. Antigen Presenting Cells

Question 8

what are the clinical implications of MHCs

Answer 8

transplantation complication
individuals with certain HLA types are predisposed to certain diseases
forensic medicine

Question 9

MHC structure

Answer 9

4 domains
two nearest the membrane resemble immunoglobulin domains
two furthest from the membrane fold together to create a groove where antigen binds

Question 10

differences in structure between MHC classes

Answer 10

class I: two subunits, one transmembrane alpha chain and a beta2 microglobulin
class II: two transmembrane chains (alpha and beta)

Question 11

how are the lower domains of an MHC held together

Answer 11

as a sandwich of beta sheets held toghether by a disulphide bridge between two cystine residues

Question 12

where are the major differences between MHC polymorphic variants

Answer 12

in the peptide-binding cleft

Question 13

how many peptides can a single MHC molecule accommodate

Answer 13

multiple

Question 14

how many peptide-MHC complexes can a single TCR recognise

Answer 14

1

Question 15

what type of T cell does each class of MHC present peptides to?

Answer 15

class 1: CD8 cytotoxic T cells
class 2: CD4 helper T cells
to remember: class*CD = 8 (1x8=8, 2x4=8)