Optimization of a murine immunization model for study of PF4/heparin antibodies

Background: Heparin-induced thrombocytopenia (HIT) is a life-threatening thrombotic illness caused by drug-dependent antibodies recognizing complexes of platelet factor 4 (PF4) and heparin. Little is known about the immune pathogenesis of HIT, in particular factors influencing PF4/heparin antibody formation. To gain insight into the biologic basis of heparin sensitization, we have recently developed an animal model using wild-type (WT) mice in which murine PF4/heparin antibodies (anti-mPF4/H) arise de novo after antigen challenge. Objectives and methods: This report describes technical refinements to the murine model and describes additional biologic features of the immune response to mPF4/heparin. Results: Our studies indicate that antibody responses to mPF4/heparin are dependent on murine strain, injection routes and doses of mPF4 and heparin. C57BL/6 mice are more immunologically responsive to mPF4/heparin antigen than BALB/c mice and robust immunization can be achieved with intravenous, but not intraperitoneal, administration of antigen. We also observe a direct relationship between initial concentrations of mPF4 and antibody levels. Additionally, we demonstrate that mPF4/H immune response in mice decays with time, is not associated with thrombocytopenia and displays characteristics of immune recall on re-exposure to antigen. Conclusions: These studies describe and characterize a murine model for studying the immunologic basis of PF4/heparin sensitization.