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. 2018 Jul 30;9:1766. doi: 10.3389/fimmu.2018.01766

Figure 1.

Figure 1

Proposed roles of mucosal-associated invariant T (MAIT) and invariant natural killer T (iNKT) cells in the lung. These unconventional T lymphocytes are present in the lung at steady state and express several chemokine- and interleukin-receptors. Bacteria, fungus, virus, pollutants, and airway allergens will directly or indirectly stimulate MAIT and iNKT cells. Cytokines produced by epithelial cells, namely, IL-25, IL-33, and thymic stromal lymphopoietin, could activate these cells. Antigen-presenting cells (APC) present antigens to MAIT and iNKT cells in the context of MR1 and CD1d molecules, respectively. Activated APC produce IL-12, IL-18, and IL-23 that will stimulate MAIT and/or iNKT cells. Following TCR-dependent or TCR-independent activation, MAIT and iNKT cells secrete IFNγ, IL-17, IL-4, or IL-13. IFNγ contributes to lung protection and promotes potential protective Th1 responses against asthma. IL-17, in turn, could have a dual effect since it is known that this cytokine promotes neutrophils recruitment and activation to protect lung from injury, but IL-17 can also enhance neutrophilic asthma severity. Finally, IL-4 and IL-13 will favor Th2 immune responses and then amplify allergic eosinophilic airway inflammation.