title: Further characterization of antibody and antigen in heparin-induced thrombocytopenia.
abstract: Patients with immune heparin-induced thrombocytopenia (HIT) possess antibodies that bind to a complex of platelet factor 4 (PF4) and heparin. We observed that HIT antibodies will also bind to PF4 alone adsorbed on polystyrene ELISA wells but not to soluble PF4 in the absence of heparin. Having developed a technique to affinity-purify anti-PF4-heparin HIT IgG, we are able to provide the first estimates of the avidity of HIT IgG. HIT IgG displayed relatively high functional affinity for both PF4-heparin (Kd = 7-30 nM) and polystyrene adsorbed PF4 alone (Kd = 20-70 nM). Furthermore, agarose beads coated with PF4 alone were almost as effective as beads coated with PF4 plus heparin in depleting HIT plasmas of anti-PF4-heparin antibodies. We conclude that the HIT antibodies which bind to polystyrene adsorbed PF4 without heparin are largely the same IgG molecules that bind PF4-heparin and therefore most HIT antibodies bind epitope(s) on PF4 and not epitope(s) formed by part of a PF4 molecule and part of a heparin molecule. Binding of PF4 to heparin (optimal) or polystyrene/agarose (suboptimal) promotes recognition of this epitope.
authors.affiliation: Centre for Thrombosis and Vascular Research, Prince of Wales Hospital, Sydney, N.S.W., Australia.
authors.forename: P M
authors.initials: PM
authors.lastname: Newman
authors.forename: B H
authors.initials: BH
authors.lastname: Chong
mesh_terms: D000368:Aged; D000906:Antibodies / Q000276:immunology; D000915:Antibody Affinity / Q000276:immunology; D000918:Antibody Specificity / Q000276:immunology; D000937:Antigen-Antibody Reactions / Q000276:immunology; D001792:Blood Platelets / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes / Q000276:immunology; D005260:Female; D006493:Heparin / Q000009:adverse effects / Q000276:immunology*; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D010978:Platelet Factor 4 / Q000276:immunology*; D012685:Sepharose / Q000494:pharmacology; D013921:Thrombocytopenia / Q000139:chemically induced / Q000276:immunology*
chemical_list: D000906:Antibodies; D000939:Epitopes; D007074:Immunoglobulin G; D010978:Platelet Factor 4; D006493:Heparin; D012685:Sepharose