A new polymorphic determinant distinct from but expressed concomitantly with an HLA‐Bw44 specificity

A new antigenic determinant defined by a monoclonal antibody (6.7) is described which displays restricted expression being present only on the cells of the immunizing donor and his father and not on a panel of over one hundred unrelated HLA‐typed cells. The determinant segregated with the HLA haplotypes of the immunizing donor's family and was shown by immunochemical and capping studies to be located on a subpopulation of HLA molecules. Further capping and antibody‐blocking studies using HLA‐typing alloantisera revealed that the 6.7‐reactive determinant was located on the same molecules that expressed the HLA‐Bw44 specificity but was a separate epitope to the polymorphic HLA specificity.