Regulatory T cells: banned cells for decades.

Regulatory T cells (Tregs), either thymic derived or peripherally induced, suppress a variety of physiological and pathological immune responses, and the absence of this cell subset has been shown to result in severe systemic autoimmunity. Since their acceptance almost two decades ago, intensive research aiming to characterize the phenotype, to elucidate the suppressive activity, and to decipher the migratory behavior of Tregs has been performed. A substantial number of studies, however, focused on understanding whether defects in Treg numbers and function contribute to the development and progression of inflammatory, autoimmune, and malignant disorders, and how Treg numbers/function might be modulated to treat patients with autoimmune diseases or cancer. In the skin, an organ that is constantly exposed to the environment, Tregs are known to be critically involved not only in the maintenance of skin homeostasis but also in the regulation of cutaneous immune responses. In this review, we present an overview on recent data concerning Treg development and expansion, the molecular mechanisms underlying their immunosuppressive activity, and the modulation of Treg function. Furthermore, we discuss the role of Tregs in cutaneous inflammatory and autoimmune disorders.