title: Determinants of PF4/heparin immunogenicity.
abstract: Heparin-induced thrombocytopenia (HIT) is an antibody-mediated disorder that occurs with variable frequency in patients exposed to heparin. HIT antibodies preferentially recognize large macromolecular complexes formed between PF4 and heparin over a narrow range of molar ratios, but the biophysical properties of complexes that initiate antibody production are unknown. To identify structural determinants underlying PF4/heparin immunogenicity, we characterized the in vitro interactions of murine PF4 (mPF4) and heparin with respect to light absorption, size, and surface charge (zeta potential). We show that PF4/heparin macromolecular assembly occurs through colloidal interactions, wherein heparin facilitates the growth of complexes through charge neutralization. The size of PF4/heparin macromolecules is governed by the molar ratios of the reactants. Maximal complex size occurs at molar ratios of PF4/heparin at which surface charge is neutral. When mice are immunized with complexes that differ in size and/or zeta potential, antibody formation varies inversely with heparin concentration and is most robust in animals immunized with complexes displaying a net positive zeta-potential. These studies suggest that the clinical heterogeneity in the HIT immune response may be due in part to requirements for specific biophysical parameters of the PF4/heparin complexes that occur in settings of intense platelet activation and PF4 release.
authors.affiliation: Division of Hematology, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Shayela
authors.initials: S
authors.lastname: Suvarna
authors.forename: Benjamin
authors.initials: B
authors.lastname: Espinasse
authors.forename: Rui
authors.initials: R
authors.lastname: Qi
authors.forename: Rauova
authors.initials: R
authors.lastname: Lubica
authors.forename: Mortimer
authors.initials: M
authors.lastname: Poncz
authors.forename: Douglas B
authors.initials: DB
authors.lastname: Cines
authors.forename: Mark R
authors.initials: MR
authors.lastname: Wiesner
authors.forename: Gowthami M
authors.initials: GM
authors.lastname: Arepally
mesh_terms: D000818:Animals; D000917:Antibody Formation; D004563:Electrochemistry; D006493:Heparin / Q000737:chemistry / Q000276:immunology*; D046911:Macromolecular Substances / Q000737:chemistry* / Q000276:immunology; D051379:Mice; D015539:Platelet Activation; D010978:Platelet Factor 4 / Q000737:chemistry / Q000276:immunology*
chemical_list: D046911:Macromolecular Substances; D010978:Platelet Factor 4; D006493:Heparin