Baka, a New Platelet‐Specific Antigen Involved in Neonatal Allo‐Immune Thrombocytopenia

Abstract

A family is described in which the mother developed platelet-specific antibodies, not directed against the antigens of the Zw(Pl^A) or the KO system. The antibodies were only detectable in the immunofluorescence test and the radioactive aqtiglobulin test on platelets, and proved to be mainly IgGl antibodies, although weak IgM antibodies of the same specificity were also detected. By cross-absorption studies, investigation of the family and a small-scale population study, it appeared that the antibodies were directed against a new antigen which we have called Bak^a. The frequency of the Bak^a phenotype in the Dutch population was 90.76%, the calculated genotype frequency 0.696. The Bak^a phenotype was neither sex-linked nor, so far as evaluable, closely linked to other platelet, red-cell, granulocyte, or HLA groups. The first child of this mother died of neonatal thrombocytopenia, the second child was unaffected. During the second pregnancy, the titre of the antibodies did not rise. The platelets of this child were found not to carry the Bak^a antigen.