Eur. J. Imrnunol. 1990. 20: 221-227 Complement regulation by S. mansoni 221 zy Moshe Marikovsky, Miriam Parizade, Ruth Arnon and Zvi FishelsonA Department of Chemical Immunology, The Weizrnann Institute of Science, Rehovot Complement regulation on the surface of cultured schistosomula and adult worms of zyx Schistosoma mansoni* Cercaria and freshly prepared schistosomula of Schistosoma mansoni are highly sensitive to complement. However, early in their maturation, the schistosomula become resistant to complement killing. This conversion is preceded by a rapid and massive release of several acetabular proteases and of the glycocalyx coat. Thus, shedding of the glycocalyx which is a major immunogen and a strong activator of the alternative pathway of complement permits the parasite to escape immune damage. Mechanically transformed schistosomula, which were cultured in a defined synthetic medium and developed complement resistance, could be converted by proteolysis to complement sensitivity.Trypsin and pronase marked- ly increased the susceptibility of cultured schistosomula to complement. The trypsin-induced complement sensitivity persisted for at least 19 h without recovery of resistance. Similar treatment with trypsin produced complete killing of adult worms by complement in absence of antibodies. Efficient killing was obtained with normal human serum (NHS),with normal guinea pig serum (GpS), and with CCdepleted HS and C4-deficient GpS indicating that the killing was mediated by the cytolytic alternative pathway of complement. Larger quantities of C3b with intact a‘ chain could be demonstrated on trypsin-treated than on non-treated schistosomula. Antibodies which were raised in rabbits by immuni- zation with the trypsin-released material bound to cultured (non-treated) schistosomula and to adult worms, and induced their killing in GpS and C4-deficient GpS. These results suggest that following release of the glycocalyx, the transforming schistosomula of S. mansoni spontaneously express a comple- ment regulatory protein(s). A similar regulator is postulated to be present on the surface of adult worms. Such regulatory molecules may serve as good targets for immunotherapy, since antibodies directed to them will inhibit their regulatory activity and thus potentiate in vivo the lytic action of complement. 1 Introduction Cercariae and freshly transformed schistosomula of Schis- tosoma mansoni are highly sensitive to the lytic action of C (reviewed in [l]). C activation in fresh normal sera is induced primarily by the glycocalyx which surrounds the cercariae and which is a strong activator of the alternative pathway [l-31. Sera obtained from immunized or chroni- cally infected animals contain complement-fixing anti- bodies which may activate the classical pathway of C [4-61. Both activation pathways effect deposition of C3b mole- cules on the surface of the parasite [2, 7, 81. Upon transformation from cercariae and incubation in synthetic medium at 37”C, schistosomula become resistant to in vitro killing by both the classical [9-111 and the alternative [2] [I 77821 zyxwvu * This work was supported in part by grants from the John D. and Catherine T. MacArthur and the Rockefeller Foundations. zyxwvut A Incumbent of the Barecha Foundation Career Development Chair. Correspondence: Zvi Fishelson, Department of Chemical Immu- nology, The Weizmann Institute of Science, P.O.Box 26, Rehovot 76100, Israel Abbreviations: aTRM: Antibodies to trypsin-released material C4d: Complement C4 deficient DSM: Defined synthetic medium Gp: Guinea pig GpS: Normal Gp serum zyxwvuts NHS: Normal human serum SBTI: Soybean trypsin inhibitor cytolytic pathways of C. Refractoriness to C-mediated killing is also expressed by in vivo derived skin, lung stage and adult worms [ll-141. Analysis of the transition of freshly prepared schistosomula from C sensitivity to resis- tance have demonstrated a rapid release of the C-activating substances (primarily the glycocalyx) [2] and of antibody- binding sites [15 ] from the schistosomula. Schistosomular serine proteases which are released from the acetabular glands may play a dual role in this conversion to resistance, both by accelerating the release of the glycocalyx and by cleaving C proteins [16, 171. Lack of C-activating substances and antigenic sites might have been sufficient to render the transformed schistoso- mula resistant to C-mediated killing. Nevertheless, the failure of antibodies which were bound to resistant stages of schistosomula through “transplanted” antigens to induce killing by C [18, 191 suggested that the schistosomula have acquired additional innate protecting mechanism(s). The present study shows that treatment of schistosomula and adult worms with trypsin converts them from being resis- tant to highly sensitive to killing by C in fresh normal human and guinea pig serum (NHS and GpS, respectively). Refractoriness to C is not recovered even after 19-h incubation of the treated schistosomula at 37°C in defined synthetic medium. Moreover, similar to trypsin treatment, antibodies raised in rabbits against the molecules cleaved by trypsin overcome the resistance of schistosomula and adult worms and allow their killing by the cytolytic alternative pathway of Gp C. zyxw 0 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1990 0014-2980/90/0101-0221$02.50/0