Immunoglobulin bound to platelets as immune complexes or specific antibody in specimens from acquired immunodeficiency syndrome and immune thrombocytopenic purpura

Abstract

Acquired immunodeficiency syndrome (AIDS), lymphadenopathy syndrome (LAS), and immune thrombocytopenic purpura (ITP) specimens were tested by an enzyme-linked immunosorbent assay (ELISA) for immunoglobulin (Ig) bound to platelets. All specimen evaluations were performed with General Diagnostic's newly developed kit procedure. The test measured but did not distinguish immune complex (IC) binding with platelet Fc receptor sites from platelet-specific antibody (PAb) binding with platelet antigen Fab-binding sites. Alkaline phosphatase-labeled antihuman IgG as conjugate detected IgG as low as 2.0 ng/ml or platelet-adsorbed, heat-aggregated IgG, simulating IC, at 2-10 ng/ml. There was a high prevalence of platelet-bound Ig in AIDS specimens (25/25) compared with normals (2/15), detected primarily by the indirect ELISA (p less than 0.001), and a preponderance of PAb in ITP specimens (5/5) compared with normals (6/22), by the direct ELISA (p less than 0.01). AIDS specimens had a geometric mean titer (GMT) of 173 ng of IgG bound/10(7) platelets, compared with the Ig from ITP, which had a GMT of 20 (p less than .0002). Monoclonal antibody to human receptors for IgG Fc fragment (anti Fc gamma R) inhibited 69% of specimens tested as having platelet-bindable antibody. Thus, the ELISA procedure would be useful in assessing but not in differentiating platelet-bound Ig in patients with AIDS and ITP and certain other clinical groups tested.