Hypobaric hypoxia promotes the production of IL-10 of lung NKT cells in HAPE rats to fight inflammation

Background: There are environment-dependent pro-inflammatory and anti-inflammatory pathways during exposure to high altitudes. Although inhibiting the inflammatory pathway can alleviate high altitude pulmonary edema (HAPE), it is currently unclear whether inflammation is the cause of edema or the result of edema in HAPE-afflicted patients. Natural killer T (NKT) cells are a subset of T cells that play an important role in a variety of lung diseases. However, its specific role in HAPE remains unclear. Methods: HAPE rat model was established under hypobaric hypoxia condition. To investigate the role of NKT cells in HAPE, phenotypic and functional changes of NKT cells and their subpopulations were analyzed by flow cytometry. To further investigate the effect of TNF-α on NKT cells, rats were given intraperitoneal injection of TNF-α, and then, NKT cells were characterized by flow cytometry. Subsequently, the levels of TNF-α in the lungs and spleens of rats were detected by ELISA, and HAPE rats were treated with curcumin. Results: Compared with normal control, the ratio of TNF-α and IL-10 secreted by lung NKT cells was decreased in HAPE rats induced by hypoxia. Further analysis showed that the mean fluorescence intensity (MFI) of TNF-α in NKT cells did not change significantly, but the MFI of IL-10 increased significantly. Moreover, the MFI of IL-10 produced by TNF-α-treated rat lung NKT cells was higher, which was completely different from spleen NKT cells. ELISA experiments indicated that TNF-α was enriched in the lung tissue of rats regardless of hypoxia, and the level of TNF-α in lung tissue was upregulated after hypoxia. Furthermore, when HAPE rats were treated with curcumin, the MFI of IL-10 in the NKT cell subsets decreased. Conclusions: NKT cells produce high levels of IL-10, which inhibits the production of lung inflammation in HAPE rats. With the increase of TNF-α level, the inhibitory effect of lung NKT cells on inflammation was further enhanced. When the level of TNF-α decreases, the anti-inflammatory effect of NKT cells also weakens accordingly. Hence, NKT cells play a protective role in HAPE rat lungs.