A New Method for the Simultaneous Quantitation of Platelet‐bound Immunoglobuin (IgG) and Complement (C3) Employing an Enzyme‐linked Immunosorbent Assay (ELISA) Procedure

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Abstract
Summary.: An ELISA technique for the quantitation of platelet‐bound IgG and C3 is described. This is an antiglobulin consumption assay using commercial horseradish peroxidase conjugated anti‐IgG and anti‐C3 antisera. The greater the amount of antiglobulin consumed by the reaction with platelets the less is available to bind to an immune adsorbent in the form of human serum‐coated polystyrene balls. This test can be calibrated by adding known quantities of IgG or C3 to the specific enzymelinked antibody and the unbound fraction of antiserum is quantitated by allowing it to react with a chromogenic substrate for the enzyme and measuring the intensity spectrophotometrically, thus establishing an inverse relationship with the amount of antigen. Platelets from normal donors and those with non‐immunological throm‐bocytopenia gave values of 1·3–15·5 ng IgG/106 platelets and 0·22–0·96 ng C3/106 platelets which are in accordance with the normal ratio of these proteins in normal serum. Fifteen patients in whom immune destruction of platelets was suspected had excess platelet‐bound IgG ranging from 30 to 450 ng IgG/106 platelets. In none of these patients could excess platelet‐bound C3 be demonstrated. Compared to the antiglobulin consumption test we have found this test to be superior both technically and in terms of sensitivity and reproducibility.