- Major histocompatibility complex:
ABBR: MHC. A group of genes on chromosome 6 that
code for the antigens that determine tissue and blood compatibility.
- In humans, histocompatibility antigens
are called human leukocyte antigens (HLA) because
they were originally discovered in large numbers on lymphocytes. There are thousands of
combinations of HLA antigens. Class I MHC antigens (HLA-A, HLA-B, and HLA-C) are found
on all nucleated cells and platelets. Class II antigens (HLA-DR, HLA-DQ, and HLA-DP) are
found on lymphocytes and antigen processing cells and are important in the specific immune
response. In tissue and organ transplantation, the extent to which the HLA or “tissue type”
of
the donor and recipient match is a major determinant of the success of the transplant.
Fig. 5-5
Schematic representation of the HLA complex and the HLA molecules. A, The
relative distances between various genes and regions on chromosome 6 are not drawn to
scale. B, MHC I and MHC II have homologous structures, although the subunit
organization and origin of the peptide in the antigen cleft are different (see text). LT,
lymphotoxin; TNF, tumor necrosis factor.
