Myeloid-derived suppressor cells (MDSCs) are a heterogeneous group of the immature myeloid cells that are derived from the myeloid progenitors with immunosuppressive functions. MDSCs are accumulated in the inflammatory sites during some autoimmune disorders, such as rheumatoid arthritis (RA) and can be an important factor in the pathogenesis of these diseases. Some research has shown the anti-inflammatory role of MDSCs during the RA progression and supports the hypothesis that MDSCs can be a potential treatment option for autoimmunity with their immunosuppressive activity. In contrast, some papers have reported the opposite effects of MDSCs, and support the hypothesis that MDSCs have a pro-inflammatory role in autoimmune disease. MDSCs functions in RA have not been fully understood, and some controversies, as well as many unanswered questions, remain. Although the two well-known subgroups of MDSCs, M-MDSC, and PMN-MDSC, seem to have different suppressive functions and regulate the immune system responses in a different manner; some studies have shown these cells are converted to each other and even to other cells under different pathological conditions. This review summarises some of the latest papers with respect to the MDSCs functions and discusses the relationship between MDSCs and inflammation in the context of rheumatoid arthritis. Graphical Abstract

Two categories of regulatory T cells (Tregs), nTreg and iTreg, play vital roles in orchestrating the integrity of a host in the course of an immune response. Tregs commonly belong to CD4+ CD25+ T cells and they are characterized by a transcription factor – forkhead box P3 (FoxP3). Within the space of the last few years, interests have been drawn to Tregs as a therapeutic tool in several settings like autoimmune disease, transplantation, and tumor disorders. As a consequence, to assess the functional properties of Tregs, namely through their ability to suppress other cells, cytokine expression, and proliferation in a variety of conditions, it is mandatory to gain better approaches to this end. This would be beneficial in designing better-than-ever therapeutic methods with regard to Tregs properties. Gaining better insights into the underlying mechanisms of immune regulation, by means of straightforward and less time-consuming techniques, will hopefully permit the therapeutic application of these cells in the control of human disorders. This review aims at going through the basic methods for Treg isolation as well the efficiency of the commonly exerted in vitro assays of Tregs-mediated immune suppression.