FOXP3 expression and frequency of regulatory T cells in healed individuals from Leishmania major infection and the asymptomatic cases

Two groups of residents in an endemic area of Leishmania major infection in Iran with positive leishmanin skin tests who were either asymptomatic or had healed cutaneous leishmaniasis lesions were compared with respect to their T helper responses. The percentages of regulatory T cells (Treg; CD4+CD25high FoxP3+) from the peripheral blood and CD4+ T cells producing intracellular cytokines (IL-4, IL-10, IL-17 and IFN-γ) from the stimulated PBMCs were evaluated by flow cytometry and the expressions of RORC and FOXP3 genes were quantified by real-time RT-PCR. T responder (CD4+CD25−) and Treg-enriched (CD4+CD25+) cells were isolated magnetically and the suppressive capacity of the latter and the cytokines (IFN-γ, TGF-β and IL-10) secreted from them were evaluated by in vitro assays. The results showed that the frequency of Treg in the studied groups were similar and Treg from both groups exhibited high yet similar suppressive capacities while significantly higher levels of FOXP3 expression was observed in the asymptomatic group. Taken together, similar frequency and suppressiveness of Treg combined with high ratios of IFN-γ/IL-10 producing CD4+ T cells were common in both groups; however the members of the asymptomatic group appeared to require higher expression of FOXP3 to maintain their immunity to re-infection.