Study of monomorphic determinants on DR molecules of HLA class II antigens

The properties of monomorphic antigenic determinants on DR molecules of HLA class II antigens were analyzed with a panel of mouse monoclonal antibodies (mabs). Competition assays and immunoblottings showed that these mabs recognize three distinct antigenic sites. The cluster of antigenic determinants specified by mabs Bra30, Bra38, HL-39, MEM-12 and L243 belongs to the first antigenic site. The second antigenic site was demonstrated only with mab Bra20. The first two antigenic sites were detected only on DR molecules and they both depended on conformation and/or association of heavy and light chains of HLA class II molecules. Finally, the third cluster of antigenic determinants recognized by mabs Bra13, Bra22, Bra70, HL-38, and HL-40 is localized on light chains of both, DR and DP, molecules of HLA class II antigens. On the contrary to the mabs against the first two antigenic sites, reactivity of mabs with the third antigenic site was not affected by denaturation of HLA class II molecule.