An immunoenzyme assay for detection of platelet antibodies and suitable for routine use is described. Purified rabbit IgG anti-human IgG antibodies are conjugated to β-galactosidase with meta-maleimidobenzoyl-hydroxysuccinimide ester as a bifunctional reagent and o-nitrophenyl-β-galactopyranoside as a substrate to evaluate the enzymatic activity of the labeled antiglobulin. The sera of 26 patients suffering from various diseases (acute leukemia, aplastic anemia and systemic lupus erythematosus) and 40 control subjects were assayed with the enzyme-labeled reagent and, for comparison, with an indirect immunofluorescence technique. Half of these patients had never been transfused. Platelet antibodies were detected by both assays in all the transfused patients except one, and in 3 out of 13 non-transfused patients. The sera of all the control subjects were negative. Quantitation of platelet antibodies was obtained by a sensitive antiglobulin absorption technique. A method for standardization of the reagents allowing comparison of results obtained in the same patient at different times and suitable for long-term follow-up studies is also described.
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