MHC and Transplantation Flashcards
What are MHC proteins?
Expressed at the cell surface and function to present ‘self’ and ‘nonself’ antigens for inspection by T cell antigen receptors.
What is the medical relevance of MHC?
Histocompatibility - major role in graft survival.
What is the chromosomal location of the MHC?
6p21.3
What antigens are encoded by the class I region?
Encodes HLA-A, B, C (‘classical’) antigens.
What antigens are encoded by the class II region?
Encodes HLA-DR, DQ, DP antigens.
What antigens are encoded by the class III region?
Encodes HSP70, TNF, C4A, C4B, C2, BF, CYP21
Where are class I antigens primarily expressed?
Found on all nucleated cells.
Where are class II antigens primarily expressed?
On B lymphocytes, dendritic cells and macrophages (professional antigen presenting cells) but expression can be induced on T lymphocytes and other cells.
What is the structure of HLA antigens?
Membrane-bound glycoproteins
What type of inheritance does MHC show?
Mendelian inheritance (1:4, 1:2, 1;4)
En-bloc from each parental chromosome (HLA-A,B,Cw, DR, DQ,DP). Each individual inherits two antigens at a given locus.
What type of expression does MHC show?
Codominant - all inherited antigens are displayed on the cell surface.
How is HLA polymorphism created?
Large number of allelic variants at each locus
Allelic variation maintained at population level due to survival advantage
What is the significance of HLA polymorphism?
Significant in terms of capacity of individual to mount an immune response in response to an antigenic challenge.
What is sensitisation?
Any event which elicits an HLA directed immune response:
- Pregnancy
- Blood transfusion
- Transfusion
What is the main function of MHC?
Bind to peptide fragments derived from pathogens and display them on the cell surface for recognition by the appropriate T-cells.