Incubation in Mice Provides a Signal for the Differentiation ofTrypanosoma cruziEpimastigotes to Trypomastigotes1

Abstract

The differentiation of T. cruzi epimastigotes into trypomastigotes was studied in diffusion chambers subcutaneously implanted in mice. Using epimastigotes of the Tulahuen strain, transformation was first evident at 16 h after implantation and reached its maximum (92% trypomastigotes) by 24 h. Shortly before their differentiation into trypomastigotes, epimastigotes developed resistance to lysis by the alternative pathway of complement. Implantation of stationary-phase (as opposed to log-phase) parasites resulted in the accumulation of large numbers of complement-resistant epimastigotes in the chambers. Epimastigotes probably pass through a complement-resistant transitional stage before differentiating into trypomastigotes and the transformation may require cell division. In a further series of experiments, epimastigotes recovered 7 h after implantation in mice differentiated into trypomastigotes when cultured in vitro for an additional 17 h at 37.degree. C. The events which trigger the morphologic transformation of epimastigotes into trypomastigotes probably can be dissociated operationally from the differentiation process itself.