Ahmad Nasser - Student Research Committee, Faculty of Medicine, Ilam University of Medical Sciences, Ilam, Iran
Afra Khosravi - Immunology Department, Faculty of Medicine, Ilam University of Medical Sciences, Ilam, Iran
Reza Azizian - Student Research Committee, Faculty of Medicine, Ilam University of Medical Sciences, Ilam, Iran

T regulatory cells play a crucial role in immunological unresponsiveness to self- antigens and in suppressing excessive immune responses deleterious to the host. T regulatory cells are produced in the thymus as a functionally mature subpopulation of T cells. They can be induced from naive T cells in the periphery and express their marker as a forkhead/winged helix transcription factor called FoxP۳. In patients with lymphomas where T regulatory cells serve as suppressor anti-tumor cytotoxicity, decreased numbers of T regulatory cells are associated with a favorable prognosis. In contrast, in patients with lymphomas where T regulatory cells function as anti-tumor cytotoxic agents, enhanced numbers of T regulatory cells are associated with a favorable prognosis. Tumors actively promote the accumulation of these cells through several mechanisms that involve activation of naturally occurring T regulatory cells as well as conversion of non-T regulatory cells into T regulatory cells. Tumor-derived prostaglandin E۲ can increase T regulatory cell activity and induce a regulatory phenotype in CD۴+CD۲۵+T cells. On the other hand, a balance between T regulatory and Th۱۷ cells is essential for maintaining homeostasis of anti-tumor immunity. Accelerating processes such as increasing the amounts of IL-۶ or IL-۱۷ can enhance FoxP۳ T regulatory cell expression and result in a lymphoma or inactivation of T cell CD۴+. This effect is the reason for malignancy and a reduction in anti-tumor immune response. In this systematic review we intend to analyze this relationship. We have collected and analyzed the majority of recently published articles on the role of T regulatory cells as a review article.