In the homologue reactivation setting, Lb-LN cells restimulated with Lb antigens produced significantly higher levels of IFN-γ and IL-6, but lower levels of IL-10 than did La-LN cells restimulated PXD101 solubility dmso with La antigens. On average, the IFN-γ/IL-10 ratios were 10:1 in the Lb/Lb cells, but only 3 : 1 in the La/La cells. In the cross-activation setting, however, Lb-LN cells restimulated with La antigens produced relatively low levels of tested cytokines, but these cells still displayed

a Th1-favoured response (with ∼10 ng/mL of IFN-γ vs. ∼1 ng/mL of IL-10). We also performed cell transfer experiments, in which 5 × 106 of CD4+ T cells purified either from the spleen of naïve mice or draining LN of Lb-infected mice (at 4 weeks) were adoptively transferred into naïve C57BL/6 mouse 1 day prior to infection with La parasites. Similar to a previously reported cross-infection study (24), we found no major differences in disease development between the infection control SB203580 and cell-transferred groups (data not shown). Collectively, the data presented here

expend our previous findings (5), confirming a strong expansion of Th1-type cells during Lb infection and a relatively weak Th1-type response during La infection. In this study, we have attempted to define the role of CD4+ T cells using several approaches, including the analysis of TCR Vβ usage and cytokine-producing cells in nonhealing versus self-healing models following infection with two New World species of Leishmania, as well as the comparative analyses of these CD4+ T cells in primary versus secondary Leishmania infections. The most important finding in this study is that the magnitude of CD4+ T-cell activation rather than TCR diversity is the main determining factor for disease outcome in murine cutaneous leishmaniasis. This conclusion is based upon the observations that multiple TCR Vβ CD4+ T cells contributed collectively and comparably to IFN-γ production and that the overall levels of IFN-γ production positively correlated with the control of the infection. In the Leishmania research field, a well-studied example of parasite-specific T cells is the LACK-specific,

TCR Vα8+ Vβ4+ CD4+ T cells, which are capable of producing high levels of IL-4 at an early stage of infection and instructing Th2 development in L. major-infected susceptible BALB/c mice (20). The identification Morin Hydrate of such pathogenic T-cell subsets felicitates the understanding of mouse susceptibility to L. major infection via multiple approaches, including the use of antagonist LACK peptides, the depletion of LACK-specific T cells and the test of LACK-based immunization regimens (25–27). At present, there is little information on TCR repertoires in CD4+ T cells specific to other Leishmania species or to protective antigens. This lack of information on the signature of pathogenic versus protective immunity hampers the development of an anti-Leishmania vaccine.