INFECTIVITY OF TRYPANOSOMA-RANGELI IN A PROMONOCYTIC MAMMALIAN-CELL LINE

The existence of an intracellular stage of Trypanosoma rangeli in the vertebrate host was evaluated by experimental infection of the U937 hi stiocytic cell line with the San Agustin strain and the Ub66-5b clone. The identity of the parasites at the beginning and end of the experim ents was confirmed through biological behavior in the vector and mamma l hosts, isoenzymes, polymerase chain reaction (PCR), and monoclonal a ntibodies. Infectivity to U937 cells of T. rangeli obtained from cultu re and salivary glands was evaluated under different experimental cond itions. These included 34 C vs. 37 C, opsonized vs. nonopsonized paras ites, and 2, 4, 6, 24, 48, and 72 hr of cell-parasite contact. Trypano soma rangeli adopted a characteristic nondividing amastigote-like form within U937 cells, which was different in size (P = 0.001) from Trypa nosoma cruzi amastigotes. Culture forms of T. rangeli were more infect ive than parasites from salivary glands (P = 0.049) but were less infe ctive than T. cruzi (P = 0.0001). Variations in temperature (34-37 C) and complement opsonization did not affect infectivity. Viability of i ntracellular forms was confirmed by feeding Rhodnius prolixus with T. rangeli-infected cells. Resistance of T. rangeli to the intracellular milieu could be an important mechanism in producing chronic infections in mammals and in the infection of triatomines.