COMPLEMENT RESISTANCE OF LEISHMANIA-AMAZONENSIS PROMASTIGOTES IS INDEPENDENT OF PARASITE PROTEASES AND LYSIS OF SENSITIVE FORMS IS NOT DUE TO NATURAL ANTIBODIES IN NORMAL HUMAN SERUM

Leishmania amazonensis promastigotes cultivated in vitro differentiate from complement-sensitive to complement-resistant forms. In order to determine the possible involvement of parasite proteases in this proce ss, L. amazonensis promastigotes were collected daily and their proteo lytic enzyme patterns analyzed using polyacrylamide gels copolymerized with gelatin. Although promastigotes at different growth stages showe d differences in protease patterns, these changes did not correlate wi th their susceptibility to complement. The major protease of promastig otes, gp63, was expressed at the same level throughout culture, regard less of the complement resistance of the promastigotes. Furthermore, i nhibitors specific for the classes of proteases found in L. amazonensi s promastigotes did not interfere with the complement-mediated killing of promastigotes, We also investigated the binding of natural antibod ies to promastigotes at different stages of growth using ELISA, Althou gh complement-sensitive promastigotes bound significantly more antibod ies from fresh normal human serum than complement-resistant promastigo tes, equivalent amounts of C3 were detected on their surfaces followin g complement activation. Moreover, serum depleted of anti-leishmania a ntibodies was as efficient in killing promastigotes as the intact seru m. These data suggest that the resistance oft. amazonensis to compleme nt killing involves strategies other than that of the regulated expres sion of endogenous proteases capable of inactivating complement compon ents, or the differential ability to bind natural antibodies that migh t interfere with complement deposition on the parasite surface.