CalDAG-GEFI deficiency protects mice from FcγRIIa-mediated thrombotic thrombocytopenia induced by CD40L and β2GPI immune complexes.

Introduction Platelet activation via the Fcγ receptor IIa (FcγRIIa) is implicated in the pathogenesis of immune complex (IC)-mediated thrombocytopenia and thrombosis (ITT). We previously showed that ICs composed of antigen and antibodies targeting CD40 ligand (CD40L) or β2 Glycoprotein I (β2GPI) induce ITT in mice transgenic for human FcγRIIa (hFcR) but not wild-type controls (which lack FcγRIIa). Here we evaluated the contribution of the guanine nucleotide exchange factor, CalDAG-GEFI, and P2Y12, key regulators of Rap1 signaling in platelets, to ITT induced by these clinically relevant ICs.