Despite Increased CD4 super(+)Foxp3 super(+) Cells within the Infection Site, BALB/c IL-4 Receptor-Deficient Mice Reveal CD4 super(+)Foxp3-Negative T Cells as a Source of IL-10 in Leishmania major Susceptibility

BALB/c IL-4R alpha super(-/-) mice, despite the absence of IL-4/IL-13 signaling and potent Th2 responses, remain highly susceptible to Leishmania major substain LV39 due exclusively to residual levels of IL-10. To address the contribution of CD4 super(+)CD25 super(+) T regulatory (Treg) cells to IL-10-mediated susceptibility, we depleted CD4 super(+)CD25 super(+) cells in vivo and reconstituted IL-4R alpha x RAG2 recipients with purified CD4 super(+)CD25 super(-) T cells. Although anti-CD25 mAb treatment significantly decreased parasite numbers in IL-4R alpha super(-/-) mice, treatment with anti-IL-10R mAb virtually eliminated L. major parasites in both footpad and dermal infection sites. In addition, IL-4R alpha x RAG2 mice reconstituted with CD4 super(+) cells depleted of CD25 super(+) Treg cells remained highly susceptible to infection. Analysis of L. major-infected BALB/c and IL-4R alpha super(-/-) inflammatory sites revealed that the majority of IL-10 was secreted by the CD4 super(+)Foxp3 super(-) population, with a fraction of IL-10 coming from CD4 super(+)Foxp3 super(+) Treg cells. All T cell IFN- gamma production was also derived from the CD4 super(+)Foxp3 super(-) population. Nevertheless, the IL-4R alpha super(-/-)-infected ear dermis, but not draining lymph nodes, consistently displayed 1.5- to 2-fold greater percentages of CD4 super(+)CD25 super(+) and CD4 super(+)Foxp3 super(+) Treg cells compared with the BALB/c-infected dermis. Thus, CD4 super(+)Foxp3 super(-) T cells are a major source of IL-10 that disrupts IFN- gamma activity in L. major-susceptible BALB/c mice. However, the increase in CD4 super(+)Foxp3 super(+) T cells within the IL-4R alpha super(-/-) dermis implies a possible IL-10-independent role for Treg cells within the infection site, and may indicate a novel immune escape mechanism used by L. major parasites in the absence of IL-4/IL-13 signaling.