CD127, also known as the interleukin-7 receptor alpha chain (IL-7Rα), is a protein that plays a pivotal role in the immune system. It serves as the specific receptor for interleukin-7 (IL-7), primarily expressed on T cells, B cells, and certain types of natural killer (NK) cells. In the thymus and bone marrow, the binding of IL-7 to CD127 facilitates the development of T-cell and B-cell precursors into mature lymphocytes. IL-7 stimulates the clonal expansion of lymphocytes expressing CD127, which is essential for the intensity and duration of immune responses. By inhibiting apoptosis, the IL-7-CD127 signaling pathway contributes to maintaining the homeostasis of peripheral lymphocytes. IL-7 also influences lymphocyte migration, homing, and effector functions, such as cytokine production and cytotoxicity. In some autoimmune diseases, such as multiple sclerosis (MS) and rheumatoid arthritis (RA), alterations in CD127 expression levels may be observed, potentially correlating with disease onset and progression.