Baka, a new platelet-specific antigen involved in neonatal allo-immune thrombocytopenia.

A family is described in which the mother developed platelet-specific antibodies, not directed against the antigens of the Zw(PlA) or the Ko system. The antibodies were only detectable in the immumofluorescence test and the radioactive antiglobulin test on platelets, and proved to be mainly IgG1 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 Baka. The frequency of the Baka phenotype in the Dutch population was 90.76%, the calculated genotype frequency 0.696. The Baka 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 Baka antigen.

Recognition of a non-HLA-ABC antigen present on B and T lymphocytes and monocytes only detectable with the indirect immunofluorescence test.

The serum of a 39-year-old male under long-term platelet transfusion therapy for hypoplastic anemia with thrombocytopenia was investigated for the presence of leukocyte and platelet antibodies after the patients had received platelet concentrates from more than 700 random donors. The serological studies of his serum revealed: (1) the absence of platelet-reactive antibodies; (2) the absence of agglutinating or cytotoxic antibodies against leukocytes; (3) the presence of at least two granulocyte-specific antibodies, one with the specificity anti-NA2 and the other with an undefined specificity, both only detectable by indirect immunofluorescence, and (4) the presence of cytotoxic-negative fluorescence-positive peripheral-blood-mononuclear-cell-reactive antibodies, not directed against HLA-A, B or C antigens. The significance and implications of these findings are briefly discussed.

A simple immunofluorescence test for the detection of platelet antibodies.

Immunofluorescence tests on platelets have always been hampered by nonspecific fluorescence caused by non-immunological binding of plasma proteins to the platelet membrane. It was found that this could be easily overcome by fixation of the cells with paraformaldehyde (PFA). By using PFA-fixed platelets, a simple method for the detection of platelet antibodies, the platelet suspension immunofluorescence test (PSIFT) was developed. PFA fixation did not alter or inactivate the platelet antigens tested. Platelet-reactive antibodies detected specifically with the PSIFT included platelet-specific agglutinins of the IgM class, non-agglutinating platelet-specific antibodies of the IgG class, drug-dependent platelet antibodies, HLA antibodies, as well as anti-A and anti-B antibodies. The sensitivity of the new test was satisfactory, as was its reproducibility. Measurement of platelet immunofluorescence was possible in a continuous flow microfluorometer, making a principle, quantitation of platelet antibodies and antigens possible.

Removal of leucocytes from whole blood and erythrocyte suspensions by filtration through cotton wool. IV. Immunization studies in rabbits.

Hetero-immunization experiments in rabbits were performed to evaluate the quantity of leucocyte antigens present in red cell suspensions prepared by the filtration method of DIEPENHORST et al., in which no intact leucocytes could be detected. It was found that the quantity of leucocyte antigens is smallest in blood filtered immediately after taking. More leucocyte-antigenic material seems to be present in blood that is filtered after storage and in frozen-thawed red cell suspensions. Evidence was obtained that granulocyte-specific antigens are more strongly immunogenic in the rabbit than lymphocyte-specific antigens or antigens common to both cells.