IL9 is mainly involved in autoimmunity, allergic reactions, and parasitic infections, and is a growth factor of T cells and mast cells; it has received increasing attention to the role of IL-9-skewed CD8+ T (Tc9) cells, mast cells, and Vδ2 T cell-derived IL-9 in tumor immunity (52, 53). This evidence concerns the gene CD8A and allergic disease.