The role of the thymus in modulating γδ T cell suppressor activity during experimental Trypanosoma cruzi infection

We have previously shown that splenic gamma delta T cells from young but not aged BALB/c mice possess suppressor activity in vivo and in vitro during the acute phase of Trypanosoma cruzi infection. The present work was undertaken to investigate the suppressor activity of gamma delta T cells from T. cruzi-infected euthymic or athymic mice and the role of the thymus in modulating non-adherent spleen cell suppressor activity during the acute phase of infection, Splenic gamma delta T cells from aged or athymic BALB/c mice reconstituted with total spleen cells or non-reconstituted did not exhibit suppressor activity when added to full allogeneic, mixed lymphocyte cultures. In contrast, splenic gamma delta T cells from young euthymic BALB/c mice showed suppressor activity in vitro. Thymectomy reduced the splenic gamma delta T cell suppressor activity of young BALB/c mice in a time-dependent manner, following a T. cruzi challenge. The continuous provision of thymocytes to aged mice, young thymectomized mice or total spleen cell-reconstituted athymic mice could re-establish the gamma delta T cell suppressor activity, Of particular significance was the observation that the depletion of gamma delta T cells during the acute phase of T. cruzi infection restored the capacity of these mice to mount a humoral immune response to a non-related antigen such as ovalbumin. These results indicate that gamma delta T cells of extrathymic origin cannot mediate suppression and that the thymus has a role in the regulation of suppression during the acute phase of T. cruzi infection.