Mechanisms of Release of Constituents from Rabbit Platelets by Antigen-Antibody Complexes and Complement

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Abstract
Two mechanisms have been described by which antigen-antibody complexes in the presence of complement induce release of vasoactive amines from rabbit platelets. The reaction of soluble antigen, antibody in excess, normal rabbit plasma and platelets caused adherence of the platelets to the immune complexes (which required the action of C3) and lysis of the platelets (which required the action of C6). The lysis was observed microscopically and was accompanied by release of vasoactive amines, nucleotides and cytoplasmic and lysosomal enzymes. The release did not require active participation of the platelet and was postulated to result from cell lysis by complement components activated by the immune complexes in or on the platelet membrane. A nonlytic, complement-dependent release of vasoactive amines resulted from immune adherence of platelets to erythrocytes or zymosan that had fixed complement components through C3. Vasoactive amines and nucleotides were released by the reaction, but not intracellular enzymes or potassium (measured with rubidium 86). Platelet energy and activated platelet esterases were required for the release, which appeared to result from the C3-induced adherence of the platelets to the particulate antigens.

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