PF4 and autoimmune thrombocytopenic purpura: In addition to ITP, infections also play an important role in the pathogenesis of heparin-induced thrombocytopenia, in which pathogenic antibodies to the complexes of platelet factor 4 (PF4) and heparin develop post-heparin exposure, leading to life-threatening complications of thrombocytopenia and thrombosis (179, 180).