The Structure of Products of the Major Histocompatibility Complex in Man

Abstract

The major histocompatibility complex (MHC) is a genetic region which encodes the major barrier to transplantation in man and in all other species which have been studied. It was first identified through mouse-breeding studies which led to the identification of the H-2 region, the second transplantation region discovered in these studies and the strongest barrier to transplantation in this species. There are at least 15 genetic loci which determine the ability of mice to exchange grafts. Little is known about the minor loci. HLA is the human analog of the H-2 region, and correspondingly the strongest of the transplantation barriers in man. The existence of other loci greatly increases the complexity of our ultimate understanding of the phenomenon of graft acceptance. The sixth human chromosome (or seventeenth mouse chromosome) contains genetic regions HLA-A, HLA-B and HLA-C (analogous to the H2-K and H2-D loci in the mouse). There are multiple alleles at each of these loci. The existence of this polymorphism and its meaning for the natural function of this region (which certainly did not evolve to prevent the exchange of surgical grafts) poses the most intriguing questions about this system. This paper will deal mainly with the products of the HLA-A and HLA-B loci. Little is known about the products of the HLA-C locus at present. The products of the HLA-D locus are defined by the mixed leucocyte culture (MLC) and are probably the human analog(s) of the mouse Ia antigen(s); some information about the probable product of this locus will also be presented.