THE ROLE OF THE THYMUS IN MODULATING GAMMA-DELTA T-CELL SUPPRESSOR ACTIVITY DURING EXPERIMENTAL TRYPANOSOMA-CRUZI INFECTION

We have previously shown that splenic gamma delta T cells from young b ut not aged BALB/c mice possess suppressor activity in vivo and in vit ro during the acute phase of Trypanosoma cruzi infection. The present work was undertaken to investigate the suppressor activity of gamma de lta T cells from T. cruzi-infected euthymic or athymic mice and the ro le of the thymus in modulating non-adherent spleen cell suppressor act ivity during the acute phase of infection, Splenic gamma delta T cells from aged or athymic BALB/c mice reconstituted with total spleen cell s or non-reconstituted did not exhibit suppressor activity when added to full allogeneic, mixed lymphocyte cultures. In contrast, splenic ga mma delta T cells from young euthymic BALB/c mice showed suppressor ac tivity in vitro. Thymectomy reduced the splenic gamma delta T cell sup pressor activity of young BALB/c mice in a time-dependent manner, foll owing 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 act ivity, Of particular significance was the observation that the depleti on of gamma delta T cells during the acute phase of T. cruzi infection restored the capacity of these mice to mount a humoral immune respons e to a non-related antigen such as ovalbumin. These results indicate t hat gamma delta T cells of extrathymic origin cannot mediate suppressi on and that the thymus has a role in the regulation of suppression dur ing the acute phase of T. cruzi infection.