CXCL10 treatment promotes reduction of IL-10+ regulatory T (Foxp3+ and Tr1) cells in the spleen of BALB/c mice infected by Leishmania infantum

Abstract American visceral leishmaniasis is caused by the protozoan Leishmania infantum. The control of the disease depends on the magnitude of the Th1 cell response and IL-10 producing regulatory T cells. Administration of chemokine, such as CXCL10, has shown promising results in the leishmaniasis treatment. Previous studies from our group have shown that CXCL10 induces a reduction in parasite burden in the spleen and a decrease in IL-10 and TGF-β production in L. infantum-infected BALB/c mice. This work investigated whether CXCL10-treatment reduces IL-10 + Treg cell populations (CD4+CD25+Foxp3+ and Tr1) and induces morphological changes in the spleen. BALB/c mice were infected and treated or not with CXCL10 on the 1st, 3rd and 7th days of infection. CXCL10-treatment was able to reduce the parasite load in the spleen in L. infantum-infected BALB/c mice and this decrease in the number of parasites correlated with the decrease in size of this organ in treated animals compared to untreated animals. 7, 23, and 45 days post-treatment (p.t.), the phenotype and frequency of IL-10 + Treg cells were evaluated by flow cytometry, and the morphological changes of the spleen were analyzed by optical microscopy. After 7 and 23 days p.t., CXCL10-treated animals showed a significant reduction of CD25-Foxp3−IL-10+ (Tr1) cells in the spleen when compared to untreated animals, whereas CD4+CD25+Foxp3+IL-10+ Treg cells reduced later at 23rd and 45th days p.t. Furthermore, while untreated animals showed a significant positive correlation between IL-10 production and Tr1 cells, in CXCL10-treated group this correlation was negative. Thus, these findings show that treatment with CXCL10 chemokine in L. infantum-infected BALB/c mice results in suppression of IL10+ Treg (Foxp3+ and Tr1) cells in the spleen, associated with a reduction in parasite load and splenomegaly.