Peritoneal macrophage activation as measured by H2O2 release and histopathology was compared between Swiss mice and Calomys callosus, a wild rodent, reservoir of Trypanosoma cruzi, during the course of infection with four strains of this parasite. In mice F and Y strain infections result in high parasitemia and mortality while with silvatic strains Costalimai and M226 parasitemia is sub-patent, with very low mortality. H2O2 release peaked at 33,6 and 59 nM/2 x 10(elevado a sexta potência) cells for strains Y and F, respectively, 48 and 50 nM/2 x 10 (elevado a sexta potência) for strains Costalimai and M226, at different days after infection. Histopathological findings of myositis, myocarditis, necrotizing artheritis and abscence of macrophage parasitism were foud for strains F and Costalimai. Y strain infection presented moderate myocarditis and myositis, with parasites multiplying within macrophages. In C. callosus all four strains resulted in patent parasitemia wich was eventually overcome, with scarce mortality. H2O2 release for strains Y or F was comparable to that of mice-peaks of 27 and 53 nM/2 x 10 (elevado a sexta potência) cells, with lower values for strains Costalimai and M226 - 16.5 and 4.6 nM/2 x 10(elevado a sexta potência)cells, respectively. Histopathological lesions with Y and F strain injected animals were comparable to those of mice at the onset of infections; they subsided completely at the later stages with Y strain and partially with F strain infected C. callosus. In Costalimai infected C. callosus practically no histopathological alterations were observed.

Calomys-callosus, roedor silvestre, que já foi encontrado naturalmente infectado pelo Trypanosoma cruzi, tem baixa suscetibilidade à infecção experimental por este protozoário. Foram feitos experimentos para avaliar a contribuição da resposta imune a essa baixa suscetibilidade. Animais foram submetidos a injeção de doses altas (200 mg/kg peso corporal) ou doses baixas (20 mg/kg peso corporal) de ciclofosfamida nos dias -1 ou -1 e +5, e inoculados com 4 x 10³ T. cruzi no dia O. Observou-se a curva de parasitemia, mortalidade e resposta de anticorpos medida por aglutinação direta de tripomastigotas. Doses de 200 mg resultaram em parasitemia e mortalidade mais elevada e supressão da resposta de anticorpos. Uma dose de 20 mg aumentou os níveis de anticorpos no 20º dia após a infecção, enquanto a administração de uma segunda dose não alterou significativamente a produção de anticorpos. Os níveis de parasitemia não diminuíram, mas pelo contrário, elevaram-se em relação aos animais testemunhos, em ambos os grupos. A transferência passiva de soro anti-T. cruzi de C. callosus resultou em parasitemia e mortalidade mais baixa nos animais imunossuprimidos. Estes resultados indicam que a resposta imune é um importante fator na resistência de C. callosus à infecção por T. cruzi.

Calomys callosus a wild rodent, previously described as harboring Trypanosoma cruzi, has a low susceptibility to infection by this protozoan. Experiments were designed to evaluate the contribution of the immune response to the resistance to T. cruzi infection exhibited by C. calossus. Animals were submitted to injections of high (200 mg/kg body weight) and low (20 mg/kg body weight) doses of cyclophosphamide on days -1 or -1 and +5, and inoculated with 4 x 10³ T. cruzi on day O. Parasitemia, mortality and antibody response as measured by direct agglutination of trypomastigotes were observed. Two hundred mg doses of cyclophosphamide resulted in higher parasitemia and mortality as well as in suppression of the antibody response. A single dose of 20 mg enhanced antibody levels on the 20th day after infection, while an additional dose did not further increase antibody production. Parasitemia levels were not depressed, but rather increased in both these groups as compared to untreated controls. Passive transfer of hyperimmune C. callosus anti-T. cruzi serum to cyclophosphamide immunosuppressed animals resulted in lower parasitemia and mortality rates. These results indicate that the immune response plays an important role in the resistance of C. callossus to T. cruzi.