Allergic asthma is characterized by airway inflammation initiated by adaptive immune responses to aeroallergens. Recent data suggest that severe asthma may be a different form of asthma rather than an increase in asthma symptoms and that innate immune responses to LPS can modulate adaptive immune responses to allergens. In this study, we evaluated the hypothesis that airway exposure to different doses of LPS induces different form of asthma. Our study showed that neutrophilic inflammation and IFN-γ expression were higher in induced sputum from severe asthma patients than from mild to moderate asthmatics. Animal experiments indicated that allergen sensitization with low-dose LPS (0.1 μg) induced type 2 asthma phenotypes, i.e., airway hyperresponsiveness, eosinophilic inflammation, and allergen-specific IgE up-regulation. In contrast, allergen sensitization with high-dose LPS (10 μg) induced asthma phenotypes, i.e., airway hyperresponsiveness and noneosinophilic inflammation that were not developed in IFN-γ-deficient mice, but unaffected in the absence of IL-4. During the allergen sensitization period, TNF-α expression was found to be enhanced by both low- and high-dose LPS, whereas IL-12 expression was only enhanced by high-dose LPS. Interestingly, the asthma phenotypes induced by low-dose LPS, but not by high-dose LPS, were completely inhibited in TNF-α receptor-deficient mice, whereas the asthma phenotypes induced by high-dose LPS were abolished in the homozygous null mutation of the STAT4 gene. These findings suggest that airway exposure levels of LPS induces different forms of asthma that are type 1 and type 2 asthma phenotypes by high and low LPS levels, respectively.

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The receptor-interacting protein kinase 3 (RIPK3) plays crucial roles in programmed necrosis and innate inflammatory responses. However, a little is known about the involvement of RIPK3 in NKT cell-mediated immune responses. Here, we demonstrate that RIPK3 plays an essential role in NKT cell function via activation of the mitochondrial phosphatase phosphoglycerate mutase 5 (PGAM5). RIPK3-mediated activation of PGAM5 promotes the expression of cytokines by facilitating nuclear translocation of NFAT and dephosphorylation of dynamin-related protein 1 (Drp1), a GTPase is essential for mitochondrial homoeostasis. Ripk3−/− mice show reduced NKT cell responses to metastatic tumour cells, and both deletion of RIPK3 and pharmacological inhibition of Drp1 protects mice from NKT cell-mediated induction of acute liver damage. Collectively, the results identify a crucial role for RIPK3-PGAM5-Drp1/NFAT signalling in NKT cell activation, and further suggest that RIPK3-PGAM5 signalling may mediate crosstalk between mitochondrial function and immune signalling.

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Summary Background High‐mobility group box 1 protein (HMGB1) belonging to endogenous danger signals prolongs eosinophil survival and acts as a chemoattractant. Objective The authors evaluated the role of HMGB1 in the pathogenesis of asthma characterized by eosinophilic airway inflammation. Methods Firstly, HMGB1 expressions in induced sputum obtained from human asthmatics were determined. This was followed by an evaluation of the role of HMGB1 in a murine model of asthma using anti‐HMGB1 antibodies. Then the effect of HMGB1 on the receptor of advanced glycation end products (RAGE) expressions on CD11b‐CD11c+ cells isolated from a murine model of asthma were measured to elucidate the mechanisms involved. Results Sputum HMGB1 expressions were markedly higher in asthmatics than in normal controls, and were positively correlated with sputum eosinophilia and sputum TNF‐α, IL‐5 and IL‐13 expressions. In a murine model of asthma, HMGB1 expressions in lung tissue and HMGB1 levels in bronchoalveolar lavage fluid were significantly elevated and eosinophilic airway inflammation, non‐specific airway hyperresponsiveness, and pathological changes were attenuated by blocking HMGB1 activity. Furthermore, we found that enhanced RAGE expressions on CD11b‐CD11c+ also significantly decreased when HMGB1 activity was blocked. Conclusion and Clinical Relevance Our findings suggest that HMGB1 plays a key role in the pathogenesis of clinical and experimental asthma characterized by eosinophilic airway inflammation.

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Asthma is a chronic airway inflammatory disease typically associated with T helper cell type 2 (Th2) cytokines. IL-32, first reported as an inducer of tumor necrosis factor (TNF)-α, is an inflammatory cytokine involved in various autoinflammatory diseases, viral infection, and cancer-related inflammation. However, the role of IL-32γ in asthma has not been clearly elucidated. In this study, the levels of IL-32γ in sputum from patients with asthma were measured by ELISA, and IL-32γ function was investigated in murine models of asthma with human IL-32γ-overexpressed transgenic (IL-32γ TG) mice. The therapeutic effect of recombinant IL-32γ (rIL-32γ) on allergic inflammation was also evaluated through bronchoalveolar lavage fluid analysis and histopathologic examinations. Sputum IL-32γ levels from patients with asthma were lower than those from healthy control subjects. In an acute mouse model of asthma, IL-32γ TG mice exhibited significantly reduced airway inflammation compared with that in wild-type mice. The production of Th1 cytokines, such as TNF-α and IFN-γ, and Th2 cytokines, such as IL-4, IL-5, and IL-13, was decreased in the lungs of IL-32γTG mice. On the contrary, the expression of IL-10 and IL-10-producing CD11b(+) monocytic cells was significantly increased in the lungs of ovalbumin-sensitized IL-32γ TG mice. In addition, rIL-32γ treatment revealed a suppressive effect on the airway inflammation in a chronic mouse model of asthma. The results of this study suggest that IL-32γ may have a preventive role in the development of allergic airway inflammation and could be a potential novel therapeutic target for bronchial asthma.

Activation of Toll-like receptor (TLR)-dependent signaling leads to the expression of genes that encode pro-inflammatory factors, such as tumor necrosis factor α (TNF-α), and this process is sustained for the duration of the inflammatory response. TLR-mediated inflammation, which occurs in two phases, depends on the TNF family member 4-1BB ligand (4-1BBL) to sustain TNF-α production during late-phase signaling. Here, we showed that Toll–interleukin-1 receptor (TIR) domain–containing adaptor protein (TIRAP) and IL-1R–associated kinase 2 (IRAK2) were required to mediate the late phase of the TLR4 response through their interaction with 4-1BBL. Expression of 4-1bbl was dependent on early TLR signaling that also induced the expression of Tnf, and the resulting 4-1BBL protein translocated to the plasma membrane, where it physically interacted with TLRs to mediate late-phase, secondary TLR signaling. TLR4–4-1BBL–mediated signaling depended on TIRAP and IRAK2, as well as a downstream complex consisting of the E3 ubiquitin ligase TRAF6, the kinase TAK1, and the adaptor protein TAB1, leading to the stimulation of mitogen-activated protein kinases. Whereas early TLR4 signaling involved the formation of a signaling complex consisting of TLR4, the adaptor proteins MyD88 and TIRAP, and IRAK2, formation of a secondary complex consisting of TLR4, 4-1BBL, TIRAP, and IRAK2 enabled late-phase signaling. Inhibition of this late-phase pathway reduced the extent of TNF-α production by mouse macrophages exposed to the TLR4 ligand lipopolysaccharide (LPS), and ameliorated LPS-induced sepsis in mice. Together, these data suggest that TIRAP and IRAK2 are critical for the sustained inflammatory response that is mediated by late-phase signaling by the TLR–4-1BBL complex.