title: Heparin-independent, PF4-dependent binding of HIT antibodies to platelets: implications for HIT pathogenesis.
abstract: Antibodies specific for platelet factor 4 (PF4)/heparin complexes are the hallmark of heparin-induced thrombocytopenia and thrombosis (HIT), but many antibody-positive patients have normal platelet counts. The basis for this is not fully understood, but it is believed that antibodies testing positive in the serotonin release assay (SRA) are the most likely to cause disease. We addressed this issue by characterizing PF4-dependent binding of HIT antibodies to intact platelets and found that most antibodies testing positive in the SRA, but none of those testing negative, bind to and activate platelets when PF4 is present without any requirement for heparin (P < .0001). Binding of SRA-positive antibodies to platelets was inhibited by chondroitinase ABC digestion (P < .05) and by the addition of chondroitin-4-sulfate (CS) or heparin in excess quantities. The findings suggest that although all HIT antibodies recognize PF4 in a complex with heparin, only a subset of these antibodies recognize more subtle epitopes induced in PF4 when it binds to CS, the major platelet glycosaminoglycan. Antibodies having this property could explain "delayed HIT" seen in some individuals after discontinuation of heparin and the high risk for thrombosis that persists for weeks in patients recovered from HIT.
authors.affiliation: Medical Sciences Institute and Blood Research Institute, BloodCenter of Wisconsin, Milwaukee, WI; Department of Pathology, Medical College of Wisconsin, Milwaukee, WI;
authors.forename: Anand
authors.initials: A
authors.lastname: Padmanabhan
authors.affiliation: Medical Sciences Institute and.
authors.forename: Curtis G
authors.initials: CG
authors.lastname: Jones
authors.affiliation: Blood Research Institute, BloodCenter of Wisconsin, Milwaukee, WI;
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Bougie
authors.affiliation: Blood Research Institute, BloodCenter of Wisconsin, Milwaukee, WI; Platelet and Neutrophil Immunology Laboratory, BloodCenter of Wisconsin, Milwaukee, WI; and.
authors.forename: Brian R
authors.initials: BR
authors.lastname: Curtis
authors.affiliation: Platelet and Neutrophil Immunology Laboratory, BloodCenter of Wisconsin, Milwaukee, WI; and Department of Medicine and.
authors.forename: Janice G
authors.initials: JG
authors.lastname: McFarland
authors.affiliation: Blood Research Institute, BloodCenter of Wisconsin, Milwaukee, WI; Department of Microbiology and Molecular Genetics, Medical College of Wisconsin, Milwaukee, WI.
authors.forename: Demin
authors.initials: D
authors.lastname: Wang
authors.affiliation: Blood Research Institute, BloodCenter of Wisconsin, Milwaukee, WI; Department of Medicine and.
authors.forename: Richard H
authors.initials: RH
authors.lastname: Aster
mesh_terms: D000906:Antibodies / Q000737:chemistry*; D001792:Blood Platelets / Q000276:immunology*; D002809:Chondroitin Sulfates / Q000737:chemistry; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes / Q000737:chemistry; D006025:Glycosaminoglycans / Q000737:chemistry; D006493:Heparin / Q000737:chemistry*; D006801:Humans; D007074:Immunoglobulin G / Q000737:chemistry; D019007:P-Selectin / Q000737:chemistry; D015539:Platelet Activation; D010978:Platelet Factor 4 / Q000737:chemistry*; D011133:Polysaccharide-Lyases / Q000737:chemistry; D011485:Protein Binding; D012701:Serotonin / Q000737:chemistry; D013921:Thrombocytopenia / Q000139:chemically induced* / Q000276:immunology*; D013927:Thrombosis / Q000139:chemically induced
chemical_list: D000906:Antibodies; D000939:Epitopes; D006025:Glycosaminoglycans; D007074:Immunoglobulin G; D019007:P-Selectin; D012701:Serotonin; D010978:Platelet Factor 4; D006493:Heparin; D002809:Chondroitin Sulfates; D011133:Polysaccharide-Lyases; C021349:heparitinsulfate lyase