Comparison of the Reactions of the Rh-Related Murine Monoclonal Antibodies BS58 and R6A

The murine monoclonal antibodies BS58 and R6A are known to recognize epitopes related to the human Rh system: neither antibody reacts with Rhnull cells and the BS58 antigen is not expressed by -D- or .D. cells. It is shown here that the numbers of BS58 and R6A antigen sites vary with Rh phenotype. Both epitopes are well represented on cells of the CDe/CDe, CDe/cDE and CDe/cde phenotypes; BS58 sites are markedly reduced on cde/cde and cDE/cde and are only just detectable on cDE/cDE cells when compared with R6A sites. The number of R6A sites per red cell ranged between 20,000 and 150,000. The evidence indicates that the BS58 epitope is not on the polypeptides carrying D or R6A, nor is it uniquely on one of the polypeptides carrying either C, c, E or e. It is suggested that the BS58 epitope is either common to all the CcED polypeptides or that it is present on a polypeptide which has not yet been identified biochemically.