Partial N-terminal amino acid sequence of rat transplantation antigens

Abstract

THE major histocompatibility complex (MHC) is a genetic region in mammals that controls various immunologically related phenomena. For example, the major histocompatibility complex of the mouse, the H–2 complex, can be divided into four major regions—K, I, S and D—by recombinational analysis^1,2. The K and D regions code for transplantation antigens, cell-surface glycoproteins of 45,000 molecular weight which elicit skin, tissue and tumour graft rejection. The I region codes for immune response genes and for the Ia poly-peptides, cell-surface glycoproteins composed of heterodimers of approximately 35,000 and 28,000 MW, respectively^3,4. The S region contains structural or regulatory genes that control the levels of certain complement components^5,6. Functional and genetic analyses of these immunological traits suggest that these apparently disparate functions may be closely linked in the major histocompatibility complex of other mammals as well as the mouse⁷. The major histocompatibility complexes of humans, guinea pigs, rats and mice have been shown to have certain significant structural homologies to one another. In rats, the MHC is designated AgB or H–1 (refs 8 and 9, respectively). To date, at least 13 haplotypes, or combinations of allelic, linked genes within AgB, have been identified, based on data from skin grafting and serological testing (ref. 10 and O. Stark, personal communication). Here we present the partial N-terminal sequences of the transplantation antigens isolated from rats of the AgB4 haplotype. Our results demonstrate that the rat AgB4 transplantation antigen is homologous to those of the mouse, human and guinea pig. The sequence data also suggest that at least two major components are present. These sequences may represent the rat homologues of the mouse K and D transplantation antigens.