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. 2009 Feb 9;119(3):504–511. doi: 10.1172/JCI36745

Figure 4. Evidence for β3 cytoplasmic domain–associated kinases in initiating eptifibatide antibody-induced platelet activation.

Figure 4

(A) Schematic representation of an eptifibatide-dependent antibody simultaneously engaging both the αIIbβ3 complex and FcγRIIa, resulting in SFK-mediated phosphorylation of FcγRIIa ITAM tyrosines, recruitment of Syk, and activation of PLCγ2, ultimately resulting in platelet aggregation and granule secretion. Note that GPIIIa-associated Fyn and Src are brought into close proximity with FcγRIIa-associated Lyn as a result of antibody-mediated bridging of the extracellular domains of these 2 receptors. SH2, Src homology 2. Cal DAG-GEF is a guanine nucleotide exchange factor for Rap1. (B) Flow cytometric analysis of αIIbβ3 (detected with mAb AP2) and FcγRIIa (detected with mAb IV.3) expression on normal versus Δ724 Glanzmann thrombasthenic (GT) patient platelets analyzed in C. Note normal levels of both. Numbers above each peak indicate the median fluorescence intensity. Adapted with permission from the American Society of Hematology (82). (C) Failure of eptifibatide-dependent antibodies to activate FcγRIIa on platelets expressing a truncated β3 cytoplasmic domain.