Platelet binding of IgG from patients with heparin-induced thrombocytopenia.
Although heparin induces immune-mediated thrombocytopenia, it has been difficult to demonstrate heparin specificity of the putative immunoglobin. Recently, however, a body of data has indicated that platelet factor 4 (PF4) is required for heparin-induced thrombocytopenia (HIT) antibody to bind to heparin. Using viable platelets in a physiologic buffer, we have now documented specific and reversible platelet binding of iodine 125-labeled IgG from 5 patients with HIT and binding of 125I-labeled F(ab')2 from 2 of them. The binding requires the presence of both heparin and PF4 in a molar ratio of approximately 1:1. We have also shown that platelet activation increases HIT antibody binding. Our data suggest that the F(ab')2 domain of HIT antibody binds to heparin-PF4 complexes that accumulate on the platelet surface when equimolar concentrations of heparin and PF4 are present.
Horne
M K
MK
Clinical Pathology Department, Warren G. Magnuson Clinical Center, National Institutes of Health, Bethesda, MD 20892, USA.
Alkins
B R
BR
D001792:Blood Platelets / Q000276:immunology* / Q000378:metabolism; D006493:Heparin / Q000008:administration & dosage / Q000009:adverse effects* / Q000627:therapeutic use; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000097:blood; D007074:Immunoglobulin G / Q000097:blood*; D007457:Iodine Radioisotopes; D015539:Platelet Activation; D010978:Platelet Factor 4 / Q000276:immunology / Q000378:metabolism; D013921:Thrombocytopenia / Q000139:chemically induced* / Q000276:immunology*
D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D007457:Iodine Radioisotopes; D010978:Platelet Factor 4; D006493:Heparin