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.