Activation of pulmonary invariant NKT cells leads to exacerbation of acute lung injury caused by LPS through local production of IFN-γ and TNF-α by Gr-1+ monocytes

Invariant NK T (iNKT) cells are known to play a critical role in the regulation of inflammatory responses in various clinical settings. In the present study, we assessed the contribution of iNKT cells to the development of acute lung injury (ALI), which was caused by intra-tracheal administration of LPS. J alpha 18 gene-disrupted mice lacking these cells underwent neutrophilic inflammatory responses in lungs at an equivalent level as control mice. Next, mice were sensitized intra-tracheally with alpha-galactosylceramide, an activator of iNKT cells, followed by challenge with LPS. In this model, mice showed severe lung injury, and all mice were killed within 72 h after LPS injection. IFN-gamma and tumor necrosis factor (TNF)-alpha were strikingly elevated in the lungs of these mice. Administration of neutralizing mAb against IFN-gamma and TNF-alpha attenuated lung injury in a histopathological analysis and improved their survival rate. Flow cytometric analysis revealed that IFN-gamma was expressed in NK cells, iNKT cells and also Gr-1(dull+)Ly-6C(+) monocytes and TNF-alpha was detected mainly in Gr-1(bright+)Ly-6G(+) neutrophils and Gr-1(dull+)Ly-6C(+) monocytes. Otherwise, in mice treated with LPS alone, IFN-gamma was not detected in the lungs and Gr-1(bright+)Ly-6G(+) neutrophil was a main cellular source of TNF-alpha production. Anti-Gr-1 mAb resulted in the attenuation of ALI and decrease in the level of these cytokines. These results indicated that activation of iNKT cells led to striking exacerbation of ALI caused by LPS and that Gr-1(+) monocytes were recruited in the lungs with expressing IFN-gamma and TNF-alpha and played an important role in the development of these responses.