Effect of rat phosphorylcholine-binding protein on platelet aggregation

Abstract

Rat serum phosphorylcholine-binding protein (PCBP), also referred to as rat C-reactive protein, is present in serum under normal physiological conditions. In the present study, PCBP is shown to inhibit, in a dose-dependent manner, ADP- and platelet-activating factor (PAF)-induced platelet aggregation, using either washed rat platelets or platelet-rich plasma from rats or humans. Rat platelets, as expected, were refractory to aggregation by PAF. However, when rabbit antiserum against PCBP was added to rat platelet-rich plasma, it resulsted in aggregation of platelets by PAF. PCBP also inhibited the PAF-induced aggregation of human platelets in a dose-dependent manner. The inhibition of ADP-induced platelet aggregation by PCBP was reversed by adding phosphorylcholine. Our results suggest that PCBP present in rat serum could be the cause of the refractory response of rat plasma to PAF. It is possible that PCBP inhibits platelet aggregation by binding to the platelet surface phospholipids.