BIOCHEMICAL-IDENTIFICATION OF THE BOVINE BLOOD-GROUP M' ANTIGEN AS A MAJOR HISTOCOMPATIBILITY COMPLEX CLASS I-LIKE MOLECULE

Absorption and elution experiments showed that it was impossible to se parate antibodies against blood group factor M' from antibodies agains t bovine lymphocyte antigen (BoLA) A16 in an antiserum showing haemoly tic activity against M' as well as lymphocytotoxic activity against Bo LA-A16. To elucidate the structural relationship between BoLA-A16 and blood group antigen M', immunoprecipitation experiments on red and whi te cell lysates isolated from M'-A16 positive and negative cattle were carried out. These results showed that M(r) 44 000 and M(r) 12 000 po lypeptides can be precipitated from both red and white cells isolated from M'-A16 positive animals, whereas no bands were seen in M'-A16 neg ative animals in precipitations with the same antibody. Precipitation with a crossreacting human beta(2)-microglobulin (beta(2)-m) specific antibody confirmed a class-I-like structure associated with beta(2)-m on M' positive red cells and the absence of such a structure on M' neg ative red cells. Sequential precipitations gave analogous results. Pro teolytic degradation by papain and V8 protease did not reveal any subs tantial difference between red and white M'-A16 positive cells, but a slight difference in the pi of the immunoprecipitable components of re d and white cells was observed. All together, this indicates that eith er the blood group antigen M' is the BoLA-A16 class I antigen or M' an d BoLA-A16 are two different class I polypeptides with the same relati ve mass, sharing identical epitopes and both associated with beta(2)-m Comparable results were obtained with M(1) and BoLA-A24.