Regulatory T cells, leptin and angiogenesis.

Regulatory T cells (Treg cells) are crucial in mediating immune homeostasis and promoting the establishment and maintenance of peripheral tolerance. Excess body weight and obesity are typified by 'low-degree' chronic inflammation and are associated with an increased risk of atherosclerosis, diabetes, fatty liver disease, autoimmune diseases and cancer. All these pathological conditions are characterized by chronic inflammation, abnormal cytokine production, elevated acute-phase reactants, and the activation of several inflammatory signaling pathways. In this context, the discovery of the adipose tissue-derived hormone leptin has shed fundamental insights on how these processes might occur. Leptin represents a link among metabolic disorders and immune tolerance; indeed, leptin can negatively affect the generation and proliferation of Treg cells, key players in this context. Treg cells play also a central role in tumor progression; different reports have proposed that tumor microenvironment can induce the recruitment of Treg cells which can promote tumor tolerance and angiogenesis through expression of suppressive molecules, cytokines and angiogenic factors (i.e. vascular endothelial growth factor, leptin). This work aims to discuss some of the most recent advances on the relationship between angiogenesis, leptin and immune tolerance, focusing on the role of Treg cell function in this context.