A new HLA antigen apparently not controlled by the known HLA loci.

The human allogeneic serum RM3 recognizes a lymphocyte structure inherited with the HLA chromosome. Population studies show several positive associations with antigens of the HLA-A and HLA-B series. Negative association have been found with antigens of the HLA-C series. Moreover the distribution of the RM3 factor is in Hardy-Weinberg equilibrium with that of the HLA-C alleles. However, serological investigations (namely the 'lysostrip' technique) bring evidence that RM3 serum does not appear to contain antibodies directed against any of the antigens of the HLA-A, B and C series. The study of a segregant family, showing a crossing over between the HLA-A and HLA-B loci, shows that the RM3 factor segregates on the side of the HLA-A locus. In conclusion, within the limits of the serological approach used, the present study presents evidence of a new serologically defined HLA locus, different from those so far described.