IL9 and asthma: Th1 and Th2 cells have been the topic of the most intense study regarding asthma’s mechanisms, with the Th1 elaborating IFN-γ, interleukin (IL)-2, and lymphotoxin, and the Th2 elaborating interleukins (IL)-4, IL-5, IL-9, IL-10, and IL-13 (65, 66).