IL-9

Alias: Interleukin-9, T-cell growth factor P40

IL-9 is a proinflammatory cytokine that was identified by its proliferative effects on T cell populations. IL-9 was historically believed to be involved in type 2 immune responses, however, recent evidence suggests IL-9 may be secreted by other T helper lineages such as TReg and TH17 in addition to a new category called TH9. This TH9 lineage can either be derived from TH2 cells with TGFβ or differentiated directly from naïve CD4+ T cells with TGFβ and IL-4. IL-9 is a member of the common cytokine receptor gamma chain-dependent family of cytokines that also includes IL-2, IL-4, IL-7, IL-15 and IL-21. IL-9 binds to a heterodimeric receptor composed of the γ chain portion (CD132) of the IL-2 receptor and the IL-9R chain. Once bound, it activates the JAK/STAT signaling pathways. Its pleiotropic effects on TH2 lymphocytes, B lymphocytes, mast cells, eosinophils, IgE production, and gut and airway epithelial cells have implicated IL-9 in asthma and other allergy-related disorders. The existence of an IL-9- mediated autocrine loop has been suggested for some malignancies such as Hodgkin’s disease and large cell anaplastic lymphoma for Hodgkin’s cell lines. IL-9 is expressed by Reed-Sternberg cells and Hodgkin lymphoma cells and some large aplastic lymphoma cells, while non-Hodgkin lymphomas and peripheral T-cell lymphomas do not express it.