Authors

F Cardillo¹; J Nihei²; J Mengel³;  ¹ Gonçalo Moniz Research Center, Fiocruz-Bahia, Brazil;  ² Gonçalo Moniz Research Center, Fiocruz, Bahia, Brazil;  ³ Oswaldo Cruz Institute, Fiocruz, Rio de Janeiro, Brazil

Discussion

Introduction: B cells are crucial players during the acute T. cruzi infection. However, very little is known about their role in the chronic phase of the disease. This study analyses the consequences of the B cell absence in C57BL/6 mice infected with low numbers of the Tulahuen T. cruzi strain. Material and Methods: C57BL/6 or C57BL/6 muMT mice were infected with the Tulahuen T. cruzi strain (50 blood trypomastigotes, i.p.). Mice that survived the acute challenge were used between 4 and 8 months after infection. The following experiments were carried out: 1- Spleen and mononuclear heart and striated muscle cells were studied by flow cytometry. 2- Cytokines were measured by ELISA in supernatants from spleen cells after in vitro cultures. Histopathological studies of the heart and muscle were performed. Results: Despite very high parasitemia and high mortality, muMT mice controlled the number of parasites in circulation. When infected with low parasite numbers, about 30% of the mice survived and progressed to the chronic phase of the disease. Four to eight months after the initial challenge, mice started to die due to infection re-aggravation. MuMT mice that succumbed to the chronic infection were all lymphopenic, and this picture was never observed in B-cell sufficient mice. Spleen cells from muMT chronically infected mice produced equivalent amounts of IL-4 and IL-10 than wt mice but lower amounts of IL-2, IL-12, and INF-g. However, the production of IL-18 was much higher than wt mice. Histopathological studies showed a more intense inflammatory infiltrate in the striate muscle and heart with higher numbers of CD4+ and CD8+ T cells infiltrating these tissues. Also, their activation state is different from wt mice as lower percentages of T cells expressing CD45Rb^low were found in these tissues. Conclusion: The results presented in the present study demonstrate that B cells are crucial to maintaining T cell numbers and functions during the chronic phase of T. cruzi infection, regulating tissue inflammation.