Abstract
The major histocompatibility complex (MHC) has attracted much attention because of its immense polymorphism, its importance in transplantation, and its indisputable role in disease susceptibility in humans and animals. Two classes of MHC have been identified. Class I MHC consists of two non-covalently attached polypeptide chains, the α chain and β2-microglobulin.The a chain is approximately 40-50 kDa in size, membrane bound, and is encoded by several genes within the MHC. Class II MHC also consists of two membrane-bound polypeptides, α and β, both of which are approximately 30 kDa in size and are encoded by genes within MHC. In fish, genes of polypeptides which contain MHC class I and class II have been identified and investigated. The size and organization of fish MHCs genes are similar to those of mammals. There are several loci encoding fish MHC and there is a high degree of polymorphism observed in the putative peptide-binding region of class I α, class II α and β chains. Thus, in spite of great sequence divergence between fish and mammalian MHC genes, their overall organizations are well conserved.
