INTERLEUKIN-9 AND ITS RECEPTOR - INVOLVEMENT IN MAST-CELL DIFFERENTIATION AND T-CELL ONCOGENESIS

Interleukin-9 (IL-9) is a multifunctional cytokine produced by activat ed TH2 clones in vitro and during TH2-like T cell responses in vivo. T he IL-9 receptor is a member of the hemopoietin receptor superfamily a nd interacts with the gamma chain of the IL-2 receptor for signal tran sduction. Various observations indicate that IL-9 is actively involved in mast cell responses by inducing the proliferation and differentiat ion of these cells, The role of IL-9 in T cell responses is less clear . Although freshly isolated normal T cells do not respond to IL-9, thi s cytokine induces the proliferation of murine T cell lymphomas in vit ro and in vivo overexpression of IL-9 results in the development of th ymic lymphomas. In the human, the existence of an IL-9-mediated autocr ine loop has been suggested for some malignancies such as Hodgkin's di sease. Other potential biological targets for IL-9 include B lymphocyt es, hematopoietic progenitors, and immature neuronal cell lines.