A PARTIAL CDNA CLONE OF TRYPOMASTIGOTE DECAY-ACCELERATING FACTOR (T-DAF), A DEVELOPMENTALLY-REGULATED COMPLEMENT INHIBITOR OF TRYPANOSOMA-CRUZI, HAS GENETIC AND FUNCTIONAL SIMILARITIES TO THE HUMAN-COMPLEMENT INHIBITOR DAF

Resistance to complement-mediated lysis in Trypanosoma cruzi is due to the expression of complement-regulatory factors by the virulent devel opmental forms of this protozoan parasite. An 87- to 93-kDa molecule, which we have termed T-DAF (trypomastigote decay-accelerating factor), is present on the surface of the parasite and inhibits complement act ivation in a manner functionally similar to the mammalian complement r egulatory component, decay-accelerating factor. In this report, we cha racterized monospecific polyclonal and monoclonal antibodies which wer e obtained from mice and rabbits immunized with fast protein liquid ch romatography-purified T-DAF. These polyclonal antibodies were shown to inhibit T-DAF activity and were capable of inducing lysis of the para sites. Both the polyclonal and monoclonal antibodies were used to scre en a cDNA expression library prepared from T. cruzi trypomastigote mRN A. From this library, we obtained a partial lambdagt11 cDNA clone whic h showed genetic and functional similarity to the human C3 convertase inhibitor DAF (A. Nicholson-Weller, J. Burge, D. T. Fearon, P. F. Well er, and K. F. Austen, J. Immunol. 129:184-189, 1982).