Trypanosoma cruzi: infectivity and virulence of trypomastigotes incubated with leukocytes and serum from patients with Chagas' disease.

An important issue for the understanding of the host-parasite relationship in Chagas' disease is the extent of the action of the immune system on the parasite. To advance our understanding of this aspect, we evaluated the effect of leukocytes and/or sera from patients with Chagas' disease on trypomastigotes of Trypanosoma cruzi. We incubated, in vitro, leukocytes and sera, from patients with Chagas' disease without evidence of heart disease (INF), patients with Chagasic cardiopathy (CDM) and healthy controls (VOL), with trypomastigotes at 37 degrees C for three hours. Mice were inoculated with parasites at the end of the incubation. We kept a record of the survival time of each animal and every three days we evaluated their Parasitemia. INF (36.4%) and CDM (42.9%) prolonged the prepatent period, but not Vol. Only CDM (57.1%) extended the survival time. The sera from CDM patients that extended the survival of mice prolonged the prepatent period. However serum alone did not extend the survival time, providing evidence that leukocytes are required to decrease the virulence of the inoculum. The capacity of leukocytes and sera, from CDM, to prolong survival time shows that the immune system of patients with Chagasic cardiomyopathy can affect the parasite more intensely than IFN. On the other hand, the higher frequency of positive xenodiagnosis in CDM (11), suggests that, in vivo, occur a down regulation of the immune response.