Major Histocompatibility Complex

Question 1

In order for tha adaptive immune system to work effectively, what do we need?

Answer 1

For an appropriate response to a foreign antigen:

• lymphocytes must recognise the antigen
• then stimulated to divide and differentiate

Question 2

How do B cells recognise antigens?

What about T cells?

Answer 2

Antigen recognition on B cells is mediated by surface immunoglobulin, and the antigen can be recognised in its native form.

On T cells, antigen recognition is mediated by T cell receptor (TCR), however, T cells only recognise parts of antigens that are expressed on cell surfaces

Question 3

Where are MHC proteins found in humans?

In humans, what can MHC molecules also be referred to as?

What is it that T cells are able to recognise?

Answer 3

MHC proteins are encoded in large clusters of genes on chromosome 6.

MHC also referred to as HLA (human leucocyte antigens)

T cells recognise combination of MHC molecule and small peptide fragment of antigen

Question 4

Name the MHC families and their members:

What are the similarities and differences of each class?

Where are they expressed?

Answer 4

Class I: HLA-A, HLA-B and HLA-C

Class II: HLA-DP, HLA-DQ and HLA-DR

Each class has distinct subunit compositions but similar 3D structures

Class I: expressed on all nucleated cells including leucocytes

Class II: expressed only on leucocytes which present antigen to T cells e.g. monocytes

Question 5

How many forms of each protein can any individual express?

How are they derived?

Answer 5

Any individual expresses inly two forms of each protein co-dominantly:

• one derived from mother, one from father
  e. g. 2 versions of HLA-A, HLA-B and HLA-C

Question 6

List some clinical implications due to the polymorphism:

Answer 6

• Tissue grafting: bone marrow/kidney transplants, skin grafts
• Certain HLA types are predisposed to certain diseases
• Forensic medicine

Question 7

What are the subunits which make up Class I MHC proteins?

What are the subunits which make up Class II MHC proteins?

Answer 7

Class I:

• alpha chain (transmembrane)
• beta 2 micro-globulin

Class II:

• alpha chain
• beta chain

Both of which are transmembrane

Question 8

Is this Class I or Class II?

Label the subunits:

Answer 8

Class I

Question 9

Is this Class I or Class II?

Label the subunits:

Answer 9

Question 10

Which cells do MHC Class I present peptides to?

MHC Class II?

Answer 10

• MHC Class I present peptides to T_cytotoxic cells
• MHC Class II present peptides to T_helper cells