TRYPANOSOMA-CRUZI - RESISTANCE TO THE PORE-FORMING PROTEIN OF CYTOTOXIC LYMPHOCYTES PERFORIN

The pore-forming protein perforin is one of the main effector molecule s which cytotoxic lymphocytes utilize to kill their targets both in vi vo and in vitro. Natural killer cells and cytotoxic T lymphocytes play an important role in host defense against a number of intracellular m icroorganisms such as virus and protozoan, but the exact way they help control infection is unknown. On the other band, many microorganisms have evolved successful escape strategies to avoid immune-cell-mediate d attack. It is thus necessary to investigate the direct interaction o f infectious microorganisms with the lyric machinery of cytotoxic lymp hocytes and other cells. In the present work we report the effect of p erforin on both a protozoan, Trypanosoma cruzi, and the infected host cell. Epimastigote, amastigote, and trypomastigote forms of T. cruzi, as well as infected macrophages, were assayed for their susceptibility to perforin based on three different criteria. T. cruzi in all three differentiation stages were resistant to purified perforin at doses up to 100-fold larger than that sufficient to kill susceptible tumor cel ls. No morphological change was observed under electron microscopy. Su rvival rates and infectivities of the treated parasites in vitro were similar to those of control parasites. Moreover, the measurement of ca lcium influx using Fura-2 to assess membrane damage revealed that T. c ruzi resist perforin attack by avoiding transmembrane pore formation. Resistance to perforin was not transferred to hot cells since infected macrophages could be easily destroyed by perforin while intracellular amastigotes remained intact. (C) 1997 Academic Press.