THE SPECIFICITY OF ANTI-HLA CLASS-II MONOCLONAL-ANTIBODIES IN CATTLE

At the Eleventh International HLA Histocompatibility Workshop, numerou s anti-HLA class II monoclonal antibodies (mAb) were tested. For sever al of the polymorphic mAb, one epitope for binding has been mapped wit hin the antigen-binding site of the class II molecules. Screening of t he available bovine DRB3 and DQB exon 2 sequences revealed that some o f the key amino acid (AA) motifs of these epitopes were present in cat tle as well, and the question was raised whether this sharing of key A A motifs might cause interspecies cross-reactivity. Eight polymorphic anti-HLA class II mAb (seven anti-HLA DRB 1 and one anti-HLA DQB) were selected for analysis of their reactivity towards bovine lymphocytes. In addition: the monomorphic anti-HLA class II mAb, 7.5.10.1, was sel ected for analysis, as this mAb was described to detect class II polym orphism in cattle. Flow cytometry and lymphocyte microcytotoxicity tes ting revealed that five of the polymorphic anti-HLA mAb were reactive with bovine lymphocytes. Furthermore, the anti-bovine reactivity cf 7. 5.10.1 was confirmed. These findings were supported by biochemical ana lysis. The anti-bovine reaction of the anti-HLA mAb did not correspond with the expected reaction, which was based on the presence of the AA , postulated to be responsible for recognition. Therefore, we suggest that the patterns of reactivity of the anti-HLA mAb are not always det ermined by one epitope.