Fabiola Cardillo

Summary: In this study, we have evaluated the production of pro‐ and anti‐inflammatory cytokines and the formation of central and effector memory T cells in mice lacking mature B cells (muMT KO). The results show that Trypanosoma cruzi infection in C57Bl/6mμ MT KO mice is intensified in relation to control mice and this exacerbation is related to low levels of inflammatory cytokines produced during the acute infection and the lower numbers of central and effector memory CD4⁺ and CD8⁺ T cells generated during the acute phase of the infection. In addition, a marked reduction in the CD8⁺ T‐cell subpopulation was observed in muMT KO infected mice. In agreement to this, the degree of tissue parasitism was increased in muMT mice and the tissue inflammatory response was much less intense in the acute phase of the infection, consistent with a deficit in the generation of effector T cells. Flow cytometry analysis of the skeletal muscle inflammatory infiltrate showed a predominance of CD8⁺ CD45Rb low in B‐cell‐sufficient C57Bl/6 mice, whereas the preponderant cell type in muMT KO skeletal muscle inflammatory infiltrate was CD4⁺ T cells. In addition, CD8⁺ T cells found in skeletal muscle from muMT KO infected mice were less activated than in control B‐cell sufficient infected mice. These results suggest that B cells may participate in the generation of effector/memory T cells. In addition and more importantly, B cells were crucial in the maintenance of central and effector memory CD8⁺ T cell, as well as the determination of the T cell cytokine functional pattern, and they may therefore account for critical aspects of the resistance to intracellular pathogens, such as T. cruzi.

This study evaluated the regulatory function of NK1.1+ cells during Trypanosoma cruzi infection. Both thymectomized (Tx C57Bl/6) and euthymic C57Bl/6 mice (C57Bl/6) were infected intraperitoneally with the Tulahuen strain. NK1.1+ cells were depleted in vivo by anti-NK1.1 mAb. Spleen cells were analyzed by flow cytometry for the expression of CD44 and CD69 on T cells. Supernatants from splenocytes were used to measure nitrite concentration (quantified by Griess reagent). Interleukin 2 and IFN-gamma levels were determined by ELISA. The protocols used herein were approved by the Institutional Committee for Ethics. Student's t or Kruskal-Wallis tests were applied, as indicated. The number of T cells expressing CD69 increased progressively during T. cruzi infection in NK1.1 cell-depleted C57Bl/6 mice. In spite of an increased early T cell activation during infection, the percentage of CD4+ CD44high T cells did not augment in NK1.1 cell-depleted C57Bl/6 mice compared with untreated C57Bl/6 controls. Serum levels of IFN-gamma in anti-NK1.1-treated mice were higher than in non-depleted animals. Con-A-stimulated spleen cell supernatants from NK1.1 cell-depleted animals contained increased levels of IL-2 and nitric oxide (NO) during early infection. After the first week of infection, NO overproduction and high levels of IFN-gamma in anti-NK1.1-tre-ated C57Bl/6 mice appeared to be related to susceptibility and hyperactivation of peripheral T cells. Finally, this study suggests a novel regulatory function of NK1.1+ cells during T. cruzi infection. Without NK1.1 cells, T lymphocytes are hyperactivated but do not differentiate to effector/memory T cells in infected C57Bl/6 mice.