Schistosoma mansoni: Complement-mediated cytotoxic activity in vitro and effect of decomplementation on acquired immunity in mice

In this study of the role of the complement system in immunity to schistosomiasis, artificially transformed Schistosoma mansoni, schistosomula were treated with serum from mice with concomitant immunity as a source of antibody (Ab) and with fresh guinea pig serum as a source of complement. Two populations of schistosomula were identifiable. Some were susceptible to the action of complement alone while others were killed only in the presence of antibody and complement. Heated and zymosan treated guinea pig sera were inactive as a source of complement. Guinea pig serum deficient in the fourth component of complement could be used as a source of complement, but it was less effective than normal guinea pig serum. An effect of the complement system in vivo was also observed. Several groups of mice with concomitant immunity were challenged with 270 to 350 cercariae of S. mansoni. Five days later schistosomula were recovered from their lungs and counted. Recovery of worms was significantly increased ( P < 0.05) in two out of three experiments in groups of animals which had been pretreated with cobra venom factor to deplete the third component of complement. These results strongly suggest that the complement system is one of the effector mechanisms in concomitant immunity in schistosomiasis.