In-vitro lysis of sensitized Trypanosoma cruzi by platelets: role of C3b receptors.

Incubation of Trypanosoma cruzi bloodstream trypomastigotes (Btrys) with C5-deficient blood in the presence of anti-T. cruzi immune mouse serum (IMS) or its IgG fraction resulted in an immediate formation of small clumps in which one could easily see platelets adhered to the parasites. After 4 h of incubation most of the clumps had disappeared and the number of the parasites was considerably reduced. Twenty-four hours later there were only a few remaining parasites. This same sequence of events was also observed when the parasites were incubated with isolated platelets in presence of IMS or its IgG fraction. When the parasites were incubated with plasma in the presence of IMS or its IgG fraction but in the absence of platelets there was strong agglutination of the parasites but no reduction in their number. Incubation of the parasites with platelets and IMS or its IgG fraction in C3-depleted plasma prevented adherence of the platelets to the parasites and their subsequent lysis. It is concluded that platelets are able to induce in-vitro lysis of the Btrys and that this phenomenon is dependent on the platelet' receptor for C3b.