The role of membrane bound complement in the aggregation of mammalian platelets by collagen

Platelets from dogs decomplemented with purified Cobra Venom Factor (CVF) lose the ability to aggregate in response to collagen stimulation. In vitro in man, dog and rabbit, and in vivo in the dog, CVF abolishes the collagen response of platelets, the effect being dose-related. Resuspension of CVF inactivated platelets in plasma containing complement resulted in a total return of sensitivity to collagen. Examination of CVF inactivated platelets with the electron microscope failed to show any marked difference from control platelets. Serotonin granules were still present and the platelets retained a discoid appearance. Incubation of platelets with antibodies to C1, C3 and C5 resulted in inhibition of the collagen response: this effect was dose-related. Light microscopy indicated that DVF does not affect the adhesion of platelets to collagen but appears to prevent subsequent aggregation. It is suggested that the complement system is involved in the induction of the platelet release reaction by collagen, and that inhibition by CVF and anticomplement antibodies is the result of a blocking of the release reaction.