Serological and biochemical analysis of the PlA1 alloantigen of human platelets.

A solid phase platelet antibody assay has been developed which rapidly and sensitively detects PlA1 antibodies. The three-step assay is performed by: (1) adhering platelets to the wheels of a microtitre plate, (2) incubating the platelets with test serum, and (3) adding radiolabelled Staphylococcal protein A which binds to the Fc domain of IgG antibodies. Immune reactions are detected by overnight autoradiography. Characterization of the PlA1 antigen was performed by using PlA1 antisera in immune precipitation assays. A 90 000 dalton molecular weight species was precipitated from PlA1 positive human and dog platelets.