Major histocompatibility complex

The major histocompatibility complex antigens are involved in the presentation of previously internalised antigen to T cells. The genes of the human major histocompatibility complex are located on the short arm of chromosome 6. They are otherwise refered to as human leucocyte antigen, or HLA.

• cell surface proteins classified as class I (also termed human leucocytic antigen [HLA] A, B and C), found on all nucleated cells and class II (termed HLA, DP, DQ and DR), found on all antigen presenting cells (APCs)

Their importance increases daily as more research is performed. Also HLA associations are often the subject for stems of a multiple choice question for professional exams. However, for the practising doctor their importance lies in:

• the association between particular genotypes and disease
• their role in rejection in transplantation