Augmentation of 1-O-alkyl-2-O-acetyl-sn-glycero-3-phosphocholine (PAF)-induced human platelet activation by C-reactive protein.

Activation of human platelets by PAF was augmented by C-reactive protein, an acute phase plasma protein. The concentration of PAF required for irreversible activation (secondary aggregation of platelet and release of serotonin) was decreased to 1/10 in the presence of C-reactive protein (CRP). The presence of CRP stimulated ADP-induced activation, whereas CRP has no effect on collagen-induced activation. Human CRP affected only human platelets, but not rabbit or guinea pig platelets. The conformational modification in CRP molecule was required for the augmentation effect, since the activity was acquired only when CRP was freeze-thawed. Conformational change of CRP on freezing and thawing was observed on CD spectrum of the protein. CRP also augmented the activation of human peripheral polymorphonuclear cells by PAF.