ADVANCES IN HLA GENETICS

The major histocompatibility complex (MHC) is a genetic system of over 70 known genes that occupies the midportion of the short arm of the s ixth chromosome (C6p) and spans about 4 million base pairs of DNA. The high-resolution typing of class I and class II MHC genes and the iden tification of genes between and near them has increased the definition of the genetic basis of immune responses and diseases of unknown etio logy such as autoimmune diseases in man. Although there are many more genetic systems that participate in the rejection of tissues and in th e immune response, the MHC plays a central role in tissue compatibilit y and immune response against cancer and infectious diseases. In this paper, the authors review evidence about the role of HLA polymorphism in the pathogenesis and development of cancer, infectious diseases, au toimmune diseases and transplantation.