Distinct contributions of CD4+ and CD8+ T cells to pathogenesis of trypanosoma brucei infection in the context of gamma interferon and interleukin-10

Abstract

Although gamma interferon (IFN-γ) and interleukin-10 (IL-10) have been shown to be critically involved in the pathogenesis of African trypanosomiasis, the contributions to this disease of CD4+ and CD8+ T cells, the major potential producers of the two cytokines, are incompletely understood. Here we show that, in contrast to previous findings, IFN-γ was produced by CD4+, but not CD8+, T cells in mice infected with Trypanosoma brucei. Without any impairment in the secretion of IFN-γ, infected CD8-/- mice survived significantly longer than infected wild-type mice, suggesting that CD8+ T cells mediated mortality in an IFN-γ-independent manner. The increased survival of infected CD8-/- mice was significantly reduced in the absence of IL-10 signaling. Interestingly, IL-10 was also secreted mainly by CD4+ T cells. Strikingly, depletion of CD4+ T cells abrogated the prolonged survival of infected CD8-/- mice, demonstrating that CD4+ T cells mediated protection. Infected wild-type mice and CD8-/- mice depleted of CD4+ T cells had equal survival times, suggesting that the protection mediated by CD4+ T cells was counteracted by the detrimental effects of CD8+ T cells in infected wild-type mice. Interestingly, CD4+ T cells also mediated the mortality of infected mice in the absence of IL-10 signaling, probably via excessive secretion of IFN-γ. Finally, CD4+, but not CD8+, T cells were critically involved in the synthesis of IgG antibodies during T. brucei infections. Collectively, these results highlight distinct roles of CD4+ and CD8+ T cells in the context of IFN-γ and IL-10 during T. brucei infections.