Concerning the cellular sources of IL-17 and IL-22, early studies suggested that both cytokines were almost exclusively co-expressed by TH17 cells, though recent data suggest that IL-17 and IL-22 may also be expressed by natural killer T cells (NKT cells), γδ T cells, and innate lymphoid cells; and interestingly, these cells produce IL-17 more rapidly than do T cells and are especially important in the early response to infection [12,35,36,39,40,41]. Here, IL17A is linked to infection.