Major Histocompatibility Complex (MHC)
A cluster of genes on chromosome 6 in humans, encoding cell surface molecules that are polymorphic and that
code for antigens which lead to rapid graft rejection between members of a single species which differ at
these loci. Several classes of protein such as MHC class I and II proteins are encoded in this region.
These in humans, are known as (HLA). Class I molecules are
designated HLA-A, B, or C. Class II molecules are designated DP, DQ or DR.
- MHC class I molecule . A molecule encoded to genes of the MHC which participates in antigen
presentation to T (CD8+) cells.
- MHC class II molecule . A molecule encoded by genes of the MHC which participates in
presentation to T (CD4+) cells.
The ability of to respond only when they 'see' the appropriate antigen
in association with "self" MHC class I or class II proteins on the antigen presenting cells is called MHC restriction .