Human C1q, isolated in pure state after affinity chromatography on IgG-Sepharose, inhibited collagen-induced aggregation and release of 14C-Serotonin from prelabeled human platelets. Platelet aggregation induced by ADP or thrombin was not inhibited by C1q. Also, the adherence of platelets to glass surfaces was significantly diminished by C1q. In contrast, aggregated C1q mimicked the effect of collagen in causing platelet aggregation and release of serotonin. It appears that monomeric C1q, which has structural similarities to collagen competes with collagen for specific sites on the platelet surface.

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This work was supported by Grants MT 1361, MT 1309 and MT 2629 from the Medical Research Council of Canada.

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Copyright © 1976 by The American Association of Immunologists, Inc.
1976
The Williams & Wilkins Company