Treatment effects on IL-9+CD4+ T cells and the cytokines influencing IL-9 production in paediatric visceral leishmaniasis.

AIMS Given the involvement of IL-9 in the immune responses to parasitic infections, we aimed to determine alterations in the levels of IL-9+CD4+ T cells and the cytokines influencing their differentiations and functions following treatment in paediatric visceral leishmaniasis (VL). METHODS AND RESULTS Eighteen VL and 20 healthy children were included. The levels of IL-9+CD4+ T cells and cytokines influencing their differentiations and functions were measured in the blood and PBMC culture supernatant at the onset of diagnosis and 1 and 2 weeks and 2 months after treatment, using flow cytometer. IL-9+CD4+ T cells, IL-2 and TNF-α were significantly higher in the blood of VL patients than those in the controls; however, following treatment, IL-9+CD4+ T cells down-regulated and IL-33 and IFN-γ significantly up-regulated. After ex vivo stimulation, although the released cytokines were not significantly different between the study groups, the levels of IL-2, IL-9 and IFN-γ significantly decreased. CONCLUSIONS The higher frequency of IL-9+CD4+ T cells and its decline following treatment implies their roles in the immunopathogenesis of VL; however, at the diagnosis onset, lower levels of serum IL-9 and its higher level in the culture supernatant may confer in vivo dysfunction of IL-9+CD4+ T cells in the acute phase of human VL.