Determinants of PF4/heparin immunogenicity.
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.
Suvarna
Shayela
S
Division of Hematology, Duke University Medical Center, Durham, NC 27710, USA.
Espinasse
Benjamin
B
Qi
Rui
R
Lubica
Rauova
R
Poncz
Mortimer
M
Cines
Douglas B
DB
Wiesner
Mark R
MR
Arepally
Gowthami M
GM
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*
D046911:Macromolecular Substances; D010978:Platelet Factor 4; D006493:Heparin