IL9 and neoplasm: IL-9 was originally described as a T cell growth factor involved in the Th2 response, but recent studies have shown that IL-9 producing T cells (Th9/Tc9) can cause tissue inflammation (56) and inhibit tumor growth by activating mast cells (57) or by indirectly attracting immature dendritic cells (DCs) and activated CD8 T cells to tumors (58).