IL17A and asthma: Additional studies have since shown that the immune basis of asthma and related disorders includes additional, more recently described cytokines and inflammatory cells, including Th17 cells that secrete IL-17A and IL-17F; innate lymphoid cells (ILC) type 2 and 3; and the epithelial cytokines IL-25, IL-33, and thymic stromal lymphopoietin.