IL-9: Proteins and Enzymes

Mouse interleukin 9 (IL-9) was originally identified as T cell-derived T cell growth factor III/P40 that could support the long term growth of certain mouse T helper clones in the absence of antigen or antigen-presenting cells. Human IL-9 was independently cloned as a novel growth factor that is mitogenic for the human megakaryoblastic leukemic cell line, M07e. Human and mouse IL-9 share 56% identity at the amino acid level. Although mouse IL-9 is active on human cells, human IL-9 is not active on mouse cells.