The Immunotherapeutic Role of Regulatory T Cells in Leishmania (Viannia) panamensis Infection

Abstract

Leishmania (Viannia) parasites are etiological agents of cutaneous leishmaniasis in the New World. Infection is characterized by a mixed Th1/Th2 inflammatory response, which contributes to disease pathology. However, the role of T regulatory cells (Treg) in Leishmania (Viannia) disease pathogenesis is unclear. Using the mouse model of chronic L. (V.) panamensis infection, we have examined the hypothesis that Treg functionality contributes to control of pathogenesis. Upon infection, T regulatory cells (CD4+Foxp3+) presented with a dysregulated phenotype, in that they produced IFN-γ, expressed Tbet and had a reduced ability to suppress T cell proliferation in vitro. Targeted ablation of Tregs resulted in enlarged lesions, increased parasite load and enhanced production of IL-17 and IFN-γ with no change in IL-10 and IL-13 levels. Thus, indicating that an increased inflammatory response was commensurate with disease exacerbation and that the remaining impaired Treg cells were important in regulation of disease pathology. Conversely, adoptive transfer of Tregs from naïve mice halted disease progression, lowered parasite burden and reduced cytokine production (IL-10, IL-13, IL-17, IFN-γ). As Tregs appeared important for controlling infection, we hypothesized the expansion of Tregs could be used as an immunotherapeutic treatment approach. As a proof of principle, chronically infected mice were treated with rIL-2-anti-IL-2 antibody complex to expand Tregs. Treatment transitorily increased numbers and percentage of Treg (draining lymph node, spleen), that resulted in reduced cytokine responses, ameliorated lesions and reduced parasite load (105-fold). Thus, immunotherapy targeting Tregs could provide an alternate treatment strategy for leishmaniasis caused by L. (Viannia) parasites.

The Src kinases Hck, Fgr, and Lyn activate Abl2/Arg to facilitate IgG-mediated phagocytosis andLeishmaniainfection

“…and Arg, or SFK inhibition alone, and none of the changes seen with single inhibition are known to facilitate healing (Ehrlich et al, 2014;Lima-Junior et al, 2013;Soong et al, 2012), with the possible exception of the decreased IL-17 secretion seen with PP2 (Sousa et al, 2014). One potential explanation for the bosutinib-induced cytokine decreases is that a lower parasite burden causes a diminished amount of cytokines to be secreted in response to L. amazonensis antigen.…”

Local Delivery of the Toll-Like Receptor 9 Ligand CpG Downregulates Host Immune and Inflammatory Responses, Ameliorating Established Leishmania (Viannia) panamensis Chronic Infection

“…The relatively high dose of 50 g of CpG was used, as it had been previously demonstrated to elicit the induction of Tregs after either systemic (28,34,47) or dermal (48,49) delivery of CpG. Notably, the downregulation of the immune and inflammatory responses and the induction of Treg activity have been recently shown in this model to ameliorate disease (17).…”

“…To take into account the lesion microenvironment in vivo, we used culture supernatants from pLAg-stimulated dLN cells of L. (V.) panamensis-infected mice, which produced the mixture of cytokines (IFN-␥, IL-10, and IL-13) made in response to infection (16,17). In Following staining with Giemsa (Fluke Analytical, Sigma-Aldrich), the mean number of parasites per macrophage (B) and the percentage of parasitized macrophages (A) were calculated by counting 100 macrophages per sample, in triplicate per determination.…”

“…4E). That this induced regulatory response would lead to healing is not surprising, as the importance of regulatory T cells in healing in L. (V.) panamensis infection has been shown (18) for human infection and, more recently, in the murine model of disease (17).…”

“…Additionally, among infections by species in the Leishmania (Viannia) subgenus, heightened inflammation is associated with more severe forms of disease (13). Recently, we discovered a beneficial role of T regulatory cells (Tregs) in controlling excessive inflammation and promoting amelioration of disease in the mouse model (17) and during the course of human disease (18). Therefore, immunotherapy directed toward downregulation of the cytokines IL-13 and IL-10 and/or increasing Treg numbers/functional capacity could potentially be effective in promoting disease resolution.…”