The early phase of the immune response of CBA mice infected with Trypanosoma cruzi.

Mice injected with 10(5) culture trypomastigotes (CT) survived the 30-day observation period while those injected with the same number of bloodstream trypomastigotes (BT) died in 10 +/- 1 days. As early as 24 h after injection of CT the mice displayed an increased resistance to Trypanosoma cruzi as indicated by an increased longevity when challenged with lethal doses of BT. The phagocytic activity of mice injected 24-72 h earlier with CT is increased, while that of mice injected with BT is decreased. The data suggest that parasite factors acting on the early phase of the immune response play a role in the outcome of the infection.