IL-7 was initially described as a stromal derived factor which is capable of inducing the growth of pre-B cells in vitro. IL-7 acts on a variety of cells through its receptor (IL-7R), a heterodimer consisting of IL-7Rα (CD127) and a common γc chain (CD132) shared by other cytokine (IL-2, IL-4, IL-9, IL-15, and IL-21) receptors. In addition, IL-7Rα is shared with TSLP. The generation of IL-7-deficient and IL-7Rα-deficient mice and monoclonal antibody blocking experiments confirmed the requirement of IL-7 for B-cell development in mice. Mutations in IL-7Rα observed in patients with severe combined immunodeficiency (SCID) also underlies the importance of IL-7 signaling in T-cell development in humans. However, the presence of B cells in these individuals suggests important differences between the role of IL-7 in murine and human lymphocyte development. Thus, although human B-cell development does not appear to require IL-7, immature human B cells do proliferate in response to IL-7. Nevertheless, most recent information suggests that IL-7 dependence in human lymphopoiesis increases during development in cord blood and bone marrow. The amino acid sequence of rat IL-7 possesses approximately 89 % and 70 % identity with mouse and human, respectively. Microarray data identified IL-7 transcripts in preovulatory follicles in rats, while IL-7Rα (CD127) and γc chain (CD132) were detected in granulosa cells and preovulatory oocytes. In vitro studies showed that IL-7 induces oocyte maturation and inhibits apoptosis in granulosa cells.