Abstract
Pure C1 subcomponents (C1q, C1r, C1s) and fragments were obtained by limited proteolysis with collagenase and pepsin. The fragments prepared with pepsin contained the collagen-like region of C1q whereas the collagenase-treated C1q had lost its collagen portion.
The different C1 subcomponents or fragment of C1q were tested for their effect on human platelets and on collagen-induced aggregation and adhesion of gel-filtered platelets. The collagenase-treated C1q was without effect in platelet collagen interaction.
The pepsin-derived fragment of C1q containing the collagen-like region inhibited platelet aggregation and adhesion to collagen. The preincubation of C1s with collagen inhibited platelet adhesion and aggregation. Studies on platelet aggregation induced by aggregated IgG showed that the complete molecule of C1q is necessary for the reaction.
The results suggest that the collagen-like region of C1q reacts with the platelet, and possibly with platelet-associated C1s or a structure similar to C1s.
