Summary: Regulatory T cells (Tregs) are a specialized subpopulation of T cells that act to suppress immune response, thereby maintaining homeostasis and self-tolerance. It has been shown that Tregs are able to inhibit T cell proliferation and cytokine production and play a critical role in preventing autoimmunity. Different subsets with various functions of Treg cells exist. Tregs can be usually identified by flow cytometry. The most specific marker for these cells is FoxP3, which is localized intracellulary. Selected surface markers such as CD25 high (high molecular density) and CD127 low (low molecular density) could serve as surrogate markers to detect Tregs in a routine clinical practice. Dysregulation in Treg cell frequency or functions may lead to the development of autoimmune disease. Therapeutical Treg modulation is considered to be a promising therapeutical approach to treat some selected disorders, such as allergies, and to prevent allograft rejection.

Summary: cd200/cd200R are highly conserved type i paired membrane glycoproteins that belong to the ig superfamily containing a two immunoglobulin -like domain (v, c). cd200 is broadly distributed in a variety of cell types, whereas CD200R is primarily expressed in myeloid and lymphoid cells. They fulfill multiple functions in regulating inflammation. the interaction between cd200/cd200R results in activation of the intracellular inhibitory pathway with Rasgap recruitment and thus contributes to effector cell inhibition. It was confirmed that the CD200R activation stimulates the differentiation of t cells to the treg subset, upregulates indoleamine 2,3 -dioxygenase activity, modulates cytokine environment from a Th1 to a Th2 pattern, and facilitates an antiinflammatory IL -10 and TGF -β synthesis. CD200/CD200R are required for maintaining self -tolerance. Many studies have demonstrated the importance of cd200 in controlling autoimmunity, inflammation, the development and spread of cancer, hypersensitivity, and spontaneous fetal loss.

CD200 and its receptor were recognized as having the multiple immunoregulatory functions. Their immunoregulatory, suppressive, and tolerogenic potentials could be very effectively exploited in the treatment of many diseases, e.g. Alzheimer disease, rheumatoid arthritis, and allergy to name only some. Many research projects are aimed to develop clinically valuable methods being based on the structure and function of these paired molecules. In this review, we would like to introduce CD200/CD200R functions in a clinical context.