IL-9 (Interleukin-9) is a TH2-type cytokine first described in the mouse as a potent T-Cell and mast cell growth factor. IL-9 has been reported to be a T-Cell derived cytokine with various effects on a variety of cell types associated with allergic inflammation. IL-9 has been shown to stimulate the proliferation of activated T-Cells, enhance the production of IgE from B-Cells, and promote the proliferation and differentiation of mast cells and hematopoietic progenitors. IL-9 is a member of the 4-helix bundle cytokine family, which includes cytokines such as IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, and IL-15. Human IL-9 consists of a 14kDa glycoprotein whose mature form is composed of 144 amino acids along with a signal sequence of 18 amino [...]