Effect of Trypanosoma cruzi membrane components on the formation of the classical pathway C3 convertase.

When T. cruzi trypomastigote forms are held at 45 degrees C for 10 min in saline they become susceptible to lysis by the alternative complement pathway. As the result of heating trypomastigotes, but not epimastigotes, substances are released into the fluid phase which inhibit EAC1,4,2,3 by inducing decay. The inhibition was most pronounced at the level of the decay of the C14b2a complex. C3 convertase of the classical pathway was also inhibited by live trypomastigote forms. These data suggest that the trypomastigote but not epimastigote forms of T. cruzi have cell surface modulators of C3 convertase that permit them to evade the lytic action of complement.