Status of the MNSs antigens on human platelets

A sensitive and specific radioimmunoassay was used to determine whether human platelets possess antigens of the MNSs blood group. Mouse monoclonal IgG anti-M and anti-N were purified by Staphylococcus protein A chromatography, labeled with 125I, and incubated with platelet pellets from donors of various MN phenotypes. Human IgG anti-M, -S, and -s were purified by absorption-elution, incubated with platelet pellets from donors of different MNSs phenotypes, washed, and incubated with 125I-labeled mouse monoclonal anti-human IgG. In both assays, the platelet pellets were centrifuged through phthalate ester oils and the radioactivity in the pellets was counted. Dose-response curves and ligand bound per cell indicated no significant difference in the binding of mouse or human anti-M and anti-N to platelets from donors of the MM, MN, or NN phenotype or of human anti-S and anti-s to platelets from donors of the Ss or ss phenotype. Contrary to many previous studies, our data indicate that the MNSs antigens are not expressed on the circulating human platelet. Therefore, antibodies to these antigens probably do not play a role in refractoriness to platelet transfusion.