IL‐33, a new member of the IL‐1 family cytokine, is involved in Th2‐type responses in a wide range of diseases and signals through the ST2 receptor expressed on many immune cells. Since the effects of IL‐33 on DCs remain controversial, we investigated the ability of IL‐33 to modulate DC functions in vitro and in vivo. Here, we report that IL‐33 activates myeloid DCs to produce IL‐6, IL‐1b, TNF, CCL17 and to express high levels of CD40, CD80 OX40L and CCR7. Importantly, IL‐33‐activated DCs prime naive lymphocytes to produce the Th2 cytokines IL‐5 and IL‐13, but not IL‐4. In vivo, IL‐33 exposure induces DC recruitment and activation in the lung. Using an OVA‐induced allergic lung inflammation model, we demonstrate that the reduced airway inflammation in ST2‐deficient mice correlates with the failure in DC activation and migration to the draining LN. Finally, we show that adoptive transfer of IL‐33‐activated DCs exacerbates lung inflammation in a DC‐driven model of allergic airway inflammation. These data demonstrate for the first time that IL‐33 activates DCs during antigen presentation and thereby drives a Th2‐type response in allergic lung inflammation.

Limited experimental evidence bridges nutrition and cancer immunosurveillance. Here, we show that ketogenic diet (KD) — or its principal ketone body, 3-hydroxybutyrate (3HB), most specifically in intermittent scheduling — induced T cell–dependent tumor growth retardation of aggressive tumor models. In conditions in which anti–PD-1 alone or in combination with anti–CTLA-4 failed to reduce tumor growth in mice receiving a standard diet, KD, or oral supplementation of 3HB reestablished therapeutic responses. Supplementation of KD with sucrose (which breaks ketogenesis, abolishing 3HB production) or with a pharmacological antagonist of the 3HB receptor GPR109A abolished the antitumor effects. Mechanistically, 3HB prevented the immune checkpoint blockade–linked upregulation of PD-L1 on myeloid cells, while favoring the expansion of CXCR3 ⁺ T cells. KD induced compositional changes of the gut microbiota, with distinct species such as Eisenbergiella massiliensis commonly emerging in mice and humans subjected to carbohydrate-low diet interventions and highly correlating with serum concentrations of 3HB. Altogether, these results demonstrate that KD induces a 3HB-mediated antineoplastic effect that relies on T cell–mediated cancer immunosurveillance.

Toll-like receptors (TLRs) such as TLR2 and TLR4 have been implicated in host response to mycobacterial infection. Here, mice deficient in the TLR adaptor molecule myeloid differentiation factor 88 (MyD88) were infected with Mycobacterium tuberculosis (MTB). While primary MyD88^–/– macrophages and DCs are defective in TNF, IL-12, and NO production in response to mycobacterial stimulation, the upregulation of costimulatory molecules CD40 and CD86 is unaffected. Aerogenic infection of MyD88^–/– mice with MTB is lethal within 4 weeks with 2 log₁₀ higher CFU in the lung; high pulmonary levels of cytokines and chemokines; and acute, necrotic pneumonia, despite a normal T cell response with IFN-γ production to mycobacterial antigens upon ex vivo restimulation. Vaccination with Mycobacterium bovis bacillus Calmette-Guérin conferred a substantial protection in MyD88^–/– mice from acute MTB infection. These data demonstrate that MyD88 signaling is dispensable to raise an acquired immune response to MTB. Nonetheless, this acquired immune response is not sufficient to compensate for the profound innate immune defect and the inability of MyD88^–/– mice to control MTB infection.

Lipoarabinomannans (LAM) and lipomannans (LM) are integral parts of the mycobacterial cell wall recognized by cells involved in the innate immune response and have been found to modulate the cytokine response. Typically, mannosylated LAM from pathogenic mycobacteria have been reported to be anti-inflammatory, whereas phosphoinositol-substituted LAM from nonpathogenic species are proinflammatory molecules. In this study, we show that LM from several mycobacterial species, including Mycobacterium chelonae, Mycobacterium kansasii, and Mycobacterium bovis bacillus Calmette-Guérin, display a dual function by stimulating or inhibiting proinflammatory cytokine synthesis through different pathways in murine primary macrophages. LM, but none of the corresponding LAM, induce macrophage activation characterized by cell surface expression of CD40 and CD86 and by TNF and NO secretion. This activation is dependent on the presence of Toll-like receptor (TLR) 2 and mediated through the adaptor protein myeloid differentiation factor 88 (MyD88), but independent of either TLR4 or TLR6 recognition. Surprisingly, LM exerted also a potent inhibitory effect on TNF, IL-12p40, and NO production by LPS-activated macrophages. This TLR2-, TLR6-, and MyD88-independent inhibitory effect is also mediated by LAM from M. bovis bacillus Calmette-Guérin but not by LAM derived from M. chelonae and M. kansasii. This study provides evidence that mycobacterial LM bear structural motifs susceptible to interact with different pattern recognition receptors with pro- or anti-inflammatory effects. Thus, the ultimate response of the host may therefore depend on the prevailing LM or LAM in the mycobacterial envelope and the local host cell receptor availability.

Objective: Inflammatory bowel diseases (IBD) have been intrinsically linked to a deregulated cytokine network, but novel therapeutic principles are urgently needed. Here we identify the interleukin (IL)-33 and its receptor ST2 as key negative regulators of wound healing and permeability in the colon of mice. Design: Expression of IL-33 and ST2 was determined by qRT-PCR, ELISA, immunohistochemistry and western-blot analysis. Wild-type and St2 ^−/− mice were used in wound healing experiments and in two experimental models of IBD triggered by 2,4,6-trinitrobenzene sulphonic acid or dextran sodium sulphate (DSS). Neutralisation of ST2 was performed by using a specific blocking antibody. Results: Nuclear localisation and enhanced expression of IL-33 in myofibroblasts and enterocytes was linked to disease involvement independently of inflammation, while the expression of ST2 was primarily restricted to the colonic epithelia. In two experimental models of IBD, genetic ablation of ST2 significantly improved signs of colitis, while a sustained epithelial expression of the cyto-protective factor connexin-43 was observed in DSS-treated St2 -deficient mice. Unexpectedly, absence of ST2 in non-hematopoietic cells was sufficient to protect against colitis. Consistently, specific inhibition of endogenous ST2-mediated signalling by treatment with neutralising antibody improved DSS-induced colitis. In addition, IL-33 treatment impaired epithelial barrier permeability in vitro and in vivo, whereas absence of ST2 enhanced wound healing response upon acute mechanical injury in the colon. Conclusions: Our study unveiled a novel non-hematopoietic function of IL-33 in epithelial barrier function and wound healing. Therefore, blocking the IL-33/ST2 axis may represent an efficient therapy in IBD.

IL-33 plays a critical role in regulation of tissue homeostasis, injury, and repair. Whether IL-33 regulates neutrophil recruitment and functions independently of airways hyperresponsiveness (AHR) in the setting of ozone-induced lung injury and inflammation is unclear. We sought to examine the role of the IL-33/ST2 axis in lung inflammation on acute ozone exposure in mice. ST2- and Il33-deficient, IL-33 citrine reporter, and C57BL/6 (wild-type) mice underwent a single ozone exposure (1 ppm for 1 hour) in all studies. Cell recruitment in lung tissue and the bronchoalveolar space, inflammatory parameters, epithelial barrier damage, and airway hyperresponsiveness (AHR) were determined. We report that a single ozone exposure causes rapid disruption of the epithelial barrier within 1 hour, followed by a second phase of respiratory barrier injury with increased neutrophil recruitment, reactive oxygen species production, AHR, and IL-33 expression in epithelial and myeloid cells in wild-type mice. In the absence of IL-33 or IL-33 receptor/ST2, epithelial cell injury with protein leak and myeloid cell recruitment and inflammation are further increased, whereas the tight junction proteins E-cadherin and zonula occludens 1 and reactive oxygen species expression in neutrophils and AHR are diminished. ST2 neutralization recapitulated the enhanced ozone-induced neutrophilic inflammation. However, myeloid cell depletion using GR-1 antibody reduced ozone-induced lung inflammation, epithelial cell injury, and protein leak, whereas administration of recombinant mouse IL-33 reduced neutrophil recruitment in Il33-deficient mice. Data demonstrate that ozone causes an immediate barrier injury that precedes myeloid cell-mediated inflammatory injury under the control of the IL-33/ST2 axis. Thus IL-33/ST2 signaling is critical for maintenance of intact epithelial barrier and inflammation.