Effects of leptin on Treg cells and the possible mechanism

Abstract

Objective To investigate the effects of leptin on Treg cells and the possible mechanism. Methods Leptin-deficient (ob/ob) mice and homologous wild-type mice were used in this study. The percentages of Treg cells in spleen tissues and peripheral blood samples were measured by flow cytometry (FCM). Differences in Treg cell functionality were compared between the two groups. Splenic CD4+ T cells, separated from the ob/ob mice and the wild-type mice by magnetic beads, were respectively cultured with leptin and anti-leptin neutralization antibody to evaluate the effects of leptin on Treg cells. Quantitative real-time PCR was performed to analyze the expression of Treg cell-related cytokines at transcriptional level. The levels of IL-10 and TGF-β in the supernatants of CD4+ T cell culture were measured with Luminex technology. Results Compared with the wild-type mice, the ob/ob mice showed higher percentages of Treg cells in both peripheral blood samples and spleen tissues [(11.56±0.72)% vs (5.47±0.81)%, (10.16±0.93)% vs (6.29±0.69)%]. Treg cells isolated from the ob/ob mice had stronger immunosuppressive effects on the proliferation of effector T (Teff) cells and the secretion of TNF-α and IFN-γ than those from the wild-type mice [TNF-α: (1.6±0.2)% vs (2.4±0.5)%, IFN-γ: (4.3±0.3)% vs (7.2±1.2)%]. The percentages of Treg cells were decreased from (12.2±1.8)% to (7.6±0.9)% upon the in vitro treatment of CD4+ T cells from the ob/ob mice with leptin and the immunosuppressive effects of Treg cells were also weakened. However, the percentages of Treg cells were increased from (7.8±0.85)% to (13.1±1.5)% upon the in vitro treatment of CD4+ T cells from the wild-type mice with anti-leptin antibody and the immunosuppressive effects of Treg cells were improved as well. Moreover, the expression of Foxp3, IL-10 and TGF-β at transcriptional level and the levels of IL-10 and TGF-β in the ob/ob group were higher than those in the wild-type group. Conclusions Leptin deficiency significantly promoted the generation of Treg cells in mice and resulted in an increased expression of Foxp3, IL-10 and TGF-β at mRNA level and elevated levels of IL-10 and TGF-β. The treatment of CD4+ T cells with leptin might inhibit the generation of Treg cells through down-regulating the transcription of Foxp3, IL-10 and TGF-β. Key words: Leptin; Treg cell; Foxp3; Interleukin 10; TGF-β