Regulatory T-cells (Treg cells) are a subset of lymphocytes that have immune suppressive properties and play a critical role in the maintenance of self-tolerance. Their regulatory function leads to protection of tissues from collateral damage triggered by immune responses against microbes and allergens, they facilitate maternal tolerance to allogeneic fetus during pregnancy and maintain homeostasis with commensal microbiota . Tregs are usually characterized as CD4+ CD25high T-cells expressing forkhead box transcription factor (FOXP3). Such phenotype is found in 5-12 % of human peripheral blood CD4+ T-cells . Tregs can be further distinguished into the so-called "natural" Tregs originating in thymus (tTreg cells) and the peripherally induced Tregs (pTreg cells) . The discrimination between tTregs and pTregs is still disputable and several markers were proposed to be the tTreg unique features: the expression of Helios transcription factor and the expression of Neutropilin-1, a receptor for members of the vascular endothelial growth factor family .  Sakaguchi S, Miyara M, Constantino CM, Hafler DA. FOXP3+ regulatory T cells in the human immune system. Nat Rev Immunol (2010) 10:490-500.  Churlaud G, Pitoiset F, Jebbawi F, Lorenzon R, Bellier B, Rosenzwajg M, Klatzmann D. Human and Mouse CD8(+)CD25(+)FOXP3(+) Regulatory T Cells at Steady State and during Interleukin-2 Therapy. Front Immunol. 2015 Apr 15,6:171.  Abbas AK, Benoist C, Bluestone JA, Campbell DJ, Ghosh S, Hori S, Jiang S, Kuchroo VK, Mathis D, Roncarolo MG, Rudensky A, Sakaguchi S, Shevach EM, Vignali DA, Ziegler SF. Regulatory T cells: recommendations to simplify the nomenclature. Nat Immunol. 2013 Apr,14(4):307-8.  Lin X, Chen M, Liu Y, Guo Z, He X, Brand D, Zheng SG. Advances in distinguishing natural from induced Foxp3(+) regulatory T cells. Int J Clin Exp Pathol. 2013,6(2):116-23.