Imunorregulação da resposta imune humoral e celular, durante a infecção experimental de camundongos BALB/c com as cepas Y, PF e SC38 de Trypanosomacruzi

Abstract

The main puipose of this investigation was to observe the imtnune response of Balb/c mouse strain as a result of infection with T. cruzi straíns which present various leveis o f virulence. The majority of the immunosuppression studies involved in the I trypanosomiasis emphasized the infection with high virulent parasite strain. In the present study it was employed parasites which present high virulence (Y strain), median virulence (SC38) and low virulence (PF). It was determined the leveis o f heterologous antíbodies against sheep red bíood cells and specific antíbodies against T. cruzi from isotypes IgGl, IgG2a and IgE in the serum samples. It was also studied the secretíon of IL-4, IL-10, IFN-y and IL-12 cytolanes by spleen cells . The results showed that the immunosuppressive activity is variable according to the degree o f virulence o f the parasites which may be related with the particular biological features o f each strain. The infection by the median virulent strain, SC38, elicited the higher production of IgG2a antíbodies when compared to the other strains. These data may indicate one possibíe mechanism to control the infection. The low virulent strain, PF, generates production o f IgGl, even though in lower levei when compared with other strains. The IgE production was detected in serum samples from animais infected with the Y and SC38 strains, but without signifícant difference. The higher leveis of IL-10 and IL-4 were observed in the supematants from spleen cells from animais infected with SC38 strain. It was observed that the early production (days 7 and 15) of IFN-y by unstimulated spleen cells was present in the animais infected with the Y and PF strains o f T. cruzi, The production o f this cytokine in the SC38 strain infected group was delayed since it was detected only by day 30 and the leveis o f secretíon of IFN-y were increasing homogeneously untíí day 90. The nitric oxide production by spleen cells basically followed the same pattem as the one found for IFN-y production.84 Taken together, the resuits obtained in the present study showed that the intrinsic immunosuppressive activity that follows the T. cruzi infection is closely related to the levei ofnitric oxide production which may determine the biological feature of each strain. Also, the IL-10 and IFN-y may act antagonistically in this immunosuppressive process. On the other hand, the production of IgG2a and IgGl may play an important role controlling I cruzi infection.