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.