0 objetivo deste trabalho foi definir se a carga parasitaria na fase aguda da doenga de Chagas experimental afeta a parasitemia, a patologia e a resposta imune na fase cr6nica. Para obtengelo de diferentes cargas parasitoirias na fase aguda, camundongos A/J foram infectados corn 103 OU 105 formas tripomastigotas de T. cruzi e analisados urn ano depois. Os animais cr6nicos infectados corn 105 formas tripomastigotas apresentaram maior nivel de parasitemia residual, maior intensidade de inflamagclo no coragtio e no moscuio esquel6tico e maior grau de ativa95o do sistema imune do que os animais infectados corn 103 formas. Em reiagclo aos parametros imuno16gicos analisados, observou-se nos animais infectados corn 105 formas: i) expansio das populag6es B220-CD5- e CD8'; ii) freq0@ncia maior de blastos nas populag6es linfocit@rias B220', CD8' e CD4'; iii) mudanga acentuada nas c61ulas CD4+ para o fen6tipo CD4+CD45RBI-ow, indicando urn aumento das c61ulas efetoras elou de mem6ria; iv) freqGC=ncias elevadas de blastos CD4+CD45RB Hig' e CD4+CD45RB Low; vi) nomero superior de c61ulas secretoras de lg principaimente IgG2a; v) niveis superiores de anticorpos IgG2a e IgGl especificos e vii) maior produgclo de IFN-Y e de IL-4. Estes resultados indicam que a carga parasitaria na fase aguda da infecggto influencia a ativagclo do sistema imune e o desenvolvimento da patologia na fase cr6nica da doenga de Chagas.

The objective of this project is to evaluate if the parasite load in the acute phase experimental Chagas' disease affects the parasitemias, the pathology and the immune response in the chronic phase. To obtain low- and high-parasite loads in the acute phase of the disease, AlJ mice were infected with 103 or 105 T. cruzi trypomastigotes of the Y strain, and treated on day 6 with Benzonidazol. One year later, chronic mice were screened for subpatent parasitemias, tissue pathology and immune response. Mice infected with the high parasite inoculum showed higher levels of chronic parasitemias, heart and striated muscle inflammation and activation of the immune system when compared to mice infected with the low¬dose inoculum. Concerning the activation of the immune system, the main findings in high-dose infected mice were: i) increased numbers of splenocytes, with preferential expansion of CD8+ and B220-CDS- cells, many of them bearing a macrophage phenotype; ii) higher frequencies of B (B220+), CD4+ and CD8+ large lymphocytes; iii) a shift of CD4+ cells towards a CD4SRBLow phenotype; iv) increased frequencies of both CD4SRBLow and CD4SRBHigh large CD4+ cells; v) augmented numbers of total Ig-secreting cells, with predominance of IgG2a¬producing cells, and; vi) increased production of IFN-y and IL-4. In addition, these mice presented lower IgM and higher IgG2a and IgG1 parasite-specific serum antibody levels. Our results indicate that the parasite load at the acute phase of T. cruzi infection influences the activation of the immune system and development of Chagas pathology at the late chronic phase of the disease.