Human visceral leishmaniasis is not associated with expansion or accumulation of Foxp3⁺ CD4 cells in blood or spleen

Natural regulatory T cells (CD4⁺ CD25⁺ Foxp3⁺), natural regulatory T cells (nTreg), play an important role in the regulation of inflammatory immune responses. However, the immunosuppressive properties of nTreg may unfavourably affect the host's ability to clear certain infections. In human visceral leishmaniasis (VL), reports on the frequency and function of nTreg are not conclusive. A limitation of our own previous studies that did not indicate a major role for Foxp3⁺ nTreg in VL pathogenesis was that Foxp3 was measured by mRNA expression alone, as other tools were not available at the time. We have in this study assessed CD4⁺CD25⁺Foxp3⁺ cells in splenic aspirates and peripheral blood mononuclear cells (PBMC) from an extensive series of patients with VL and endemic controls (EC) by flow cytometry (FACS). The results do not show increased frequencies of Foxp3⁺ cells in patient with VL pre- and post-treatment, neither were they elevated when compared to PBMC of EC. We conclude that active VL is not associated with increased frequencies of peripheral Foxp3 Treg or accumulation at the site of infection.