title: Intrathymic IL-7: the where, when, and why of IL-7 signaling during T cell development.
abstract: The thymus is the birthplace of all T lineage cells. But the thymus is also a cradle as it provides the environment for further maturation and differentiation of immature thymocytes. While many factors contribute to make the thymus a unique place for T cell development, here we review the essential role of intrathymic interleukin-7 (IL-7). In the absence of IL-7 signaling, survival, proliferation and differentiation of immature thymocytes are all severely impaired. Consequently, IL-7 is critical to nurture and guide T precursor cells through the diverse steps of thymic maturation. Interestingly, even as IL-7 signaling is such a critical factor, IL-7 signaling must be also actively suppressed during specific stages of T cell differentiation. These contradictory observations are puzzling but can be satisfactorily explained when understanding the developmental context of IL-7 signaling. In this regard, here we will discuss the spatiotemporal expression of intrathymic IL-7 and address the stage-specific effects of IL-7 signaling in developing thymocytes. Specifically, we will review other facets of intrathymic IL-7 beyond its role as a pro-survival factor and so clarify and reaffirm the unique role of IL-7 as a prime factor in T cell development and differentiation.
authors.affiliation: Exp. Immunol. Branch, National Cancer Institite/NIH, 10 Center Drive, Bethesda, MD 20892-1360, United States.
authors.forename: Changwan
authors.initials: C
authors.lastname: Hong
authors.forename: Megan A
authors.initials: MA
authors.lastname: Luckey
authors.forename: Jung-Hyun
authors.initials: JH
authors.lastname: Park
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D006801:Humans; D015851:Interleukin-7 / Q000276:immunology* / Q000378:metabolism; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology*
chemical_list: D015851:Interleukin-7