performed experiments and analyzed data. Qinghai Ye provided patient tissue samples. Qiongzhu Dong, Hirohito Yamaguchi, and Yi Du provided scientific input and critical cells. Jennifer L. Hsu revised the manuscript. Mien-Chie Hung supervised the entire project, designed the experiments, analyzed data, and wrote the manuscript.

Hapten induced contact hypersensitivity (CHS) in the skin is a delayed type cellular immune response which can be mediated by CD8+ T cells that produce IFN-γ or IL-17. However, mechanisms for these cytokines in the elicitation of CHS remain to be fully elucidated. Here we show that adoptive transfer of CHS with hapten primed wild type CD8+ T cells is reduced in IFN-γR−/− or IL-17R−/− mice compared to wild type controls. The infiltration of granulocytes and macrophages in the hapten challenged skin of IL-17R−/− recipients is significantly reduced whereas it is less affected in IFN-γR−/− recipients although CD8+ T cell infiltration is inhibited in both recipients. In contrast, the activity of reactive oxidative species is significantly inhibited in IFN-γR−/− but is less affected in IL-17R−/− recipients. Further analysis reveals that the expression of chemokines and cytokines is differentially regulated in the hapten challenged skin of IFN-γR−/− or IL-17R−/− recipients compared to wild type controls. Interestingly, injection of recombinant IL-17 in the skin induces inflammation with a high level of leukocyte infiltration whereas injection of IFN-γ induces inflammation with a high level of reactive oxidative species. Moreover, neutralization of IL-17 in IFN-γR−/− or IFN-γ in IL-17R−/− mice further suppresses the adoptive transfer of CHS by hapten primed wild type CD8+ T cells. The study demonstrates that IFN-γ and IL-17 mediate the elicitation of CHS by different mechanisms and that both cytokines are required for optimal responses. This outcome improves understanding of pathogenesis and provides new insights into therapeutic strategies for CHS.

Severe influenza A virus infection causes high mortality and morbidity worldwide due to delayed antiviral treatment and inducing overwhelming immune responses, which contribute to immunopathological lung injury. Sirolimus, an inhibitor of mammalian target of rapamycin (mTOR), was effective in improving clinical outcomes in patients with severe H1N1 infection; however, the mechanisms by which it attenuates acute lung injury have not been elucidated. Here, delayed oseltamivir treatment was used to mimic clinical settings on lethal influenza A (H1N1) pdm09 virus (pH1N1) infection mice model. We revealed that delayed oseltamivir plus sirolimus treatment protects mice against lethal pH1N1 infection by attenuating severe lung damage. Mechanistically, the combined treatment reduced viral titer and pH1N1-induced mTOR activation. Subsequently, it suppressed the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome-mediated secretion of interleukin (IL)-1β and IL-18. It was noted that decreased NLRP3 inflammasome activation was associated with inhibited nuclear factor (NF)-κB activation, reduced reactive oxygen species production and increased autophagy. Additionally, the combined treatment reduced the expression of other proinflammatory cytokines and chemokines, and decreased inflammatory cell infiltration in lung tissue and bronchioalveolar lavage fluid. Consistently, it inhibited the mTOR-NF-κB-NLRP3 inflammasome-IL-1β axis in a lung epithelial cell line. These results demonstrated that combined treatment with sirolimus and oseltamivir attenuates pH1N1-induced severe lung injury, which is correlated with suppressed mTOR-NLRP3-IL-1β axis and reduced viral titer. Therefore, treatment with sirolimus as an adjuvant along with oseltamivir may be a promising immunomodulatory strategy for managing severe influenza.