It was recently reported that IL-17 and IL-22, produced by T helper type 17 (Th17) cells and NK cells, play important roles in TB protective immune response89. In vitro experiments showed that IL-22 can directly affect human macrophages, improving cells' protective immunity against TB infection10. IL-22 has also been shown to induce host defense genes, and thus is crucial for controlling the gram-negative pulmonary pathogen, Klebsiella pheumaniae11. Knock-out study observed that IL-22 null mice showed increased intestinal epithelial damage, systemic bacterial burden and mortality after Citrobacter rodentium infection12. It was also reported that IL-22 can inhibit intracellular mycobacterial growth by enhancing phagolysosomal fusion, which contributes to the immune defenses of NK cells against M. tuberculosis10.