The Major Histocompatibility Complex and Its Biological Function

Abstract

It was one of the very early findings in transplantation research that the survival of grafted organs was largely dependent on the degree of genetic similarity between donor and recipient. Selective breeding in connection with transplantation experiments in mice has led to the identification of a number of independent genetic systems, all of which play a role in the rejection of allografts (Histocompatibility Systems = H-Systems). In all mammalian species studied so far one has been able to isolate one system, which is of paramount importance for transplantation. This system in each species is now generally referred to as the major histocompatibility complex (MHC). The current knowledge about the MHC resulted from widely differing approaches depending on the population structure of the species investigated: in rodents the availability of inbred strains and the possibility of selective breeding formed a major advantage in the analysis of the biological function of the chromosomal region. In the outbred species such as dog, rhesus monkey and man, one has to resort to the laws of population genetics. In man, two unrelated individuals have to go back for very many generations to come to the latest common ancestor chromosome in relation to the MHC. In this long time very many recombinations must have occurred, separating even very closely linked genes.