A Class II monoclonal antibody specific for the RT1.B, rather than the RT1.D, product of the rat major histocompatibility complex

An allospecific monoclonal antibody, 79.7.5., has been shown to be specific for a Class II histocompatibility product of the ACI (RT1.AaBaDa) rat. To further specify the reaction of this antibody to the B or D locus Class II products of RT1, we examined the binding of this antibody to peripheral blood lymphocytes (PBLs) of the WRC rat (haplotype RT1.AnBnDa). Radiolabelled monoclonal antibody 79.7.5. did not bind to PBLs from the WRC rat, but it did bind to PBLs from the WRA rat (RT1.AdBaDa) and the DA (RT1.AaBaDa) rat. These results were confirmed using radiolabelled Staphylococcus protein A in an indirect binding assay. In addition, binding of 79.7.5 could be inhibited by alloantiserum BN anti-BN.1A (DA) (directed against AaBaDa) but not by BN anti WRC (directed against Da). These data demonstrate that monoclonal antibody 79.7.5. reacts with the a allele product of RT1.B rather than RT1.D. This antibody can be used to probe the structures and functional roles of different Class II products of the rat major histocompatibility complex.