Interleukin 9 (IL-9) has pleiotropic functions in the immune system and signals through its specific IL-9 receptor (IL-9R) (Renauld et al.). IL-9/IL-9R signaling pathway mainly targets the downstream activation of JAK/STAT (janus kinase/signal transducer and activator of transcription) and subsequent phosphorylation cascades initiated by multiple kinases including IRS–PI3K–PKB (insulin receptor substrate, phosphatidyl-inositol 3-kinases, protein kinase-B) and ERK (Knoops & Renauld; Fontaine et al.). IL-9 has been shown to have a role in Th1/Th17-mediated inflammation and in regulatory T cell responses (Singh et al.; Goswami & Kaplan). IL-9/IL-9R signaling pathway represents a novel endogenous anti-apoptotic mechanism for cortical neurons (Fontaine et al.). IL-9 secreting T cells, termed Th9 cells, contribute to both effective immunity and immunopathological disease, and have been shown to have a role in the treatment of allergic and autoimmune disease (Kaplan et al.).