N-acetylglucosamine-6-O sulfation on intestinal mucins prevents obesity and intestinal inflammation by regulating gut microbiota.

Intestinal mucins play an essential role in the defense against bacterial invasion and the maintenance of gut microbiota, which is instrumental in the regulation of host immune systems; hence, its dysregulation is a hallmark of metabolic disease and intestinal inflammation. However, the mechanism by which intestinal mucins control the gut microbiota as well as disease phenotypes remains nebulous. Herein, we report that N-acetylglucosamine (GlcNAc)-6-O sulfation of O-glycans on intestinal mucins performs a protective role against obesity and intestinal inflammation. Chst4-/- mice, lacking GlcNAc-6-O sulfation of the mucin O-glycans, showed significant weight gain and increased susceptibility to dextran sodium sulfate-induced colitis as well as colitis-associated cancer accompanied by significantly reduced immunoglobulin A (IgA) production caused by an impaired T follicular helper cell-mediated IgA response. Interestingly, the protective effects of GlcNAc-6-O sulfation against obesity and intestinal inflammation depend on the gut microbiota, evidenced by the modulation of the gut microbiota by cohousing or microbiota transplantation reversing disease phenotypes and IgA production. Collectively, our findings provide insight into the significance of host glycosylation, more specifically GlcNAc-6-O sulfation on intestinal mucins, in protecting against obesity and intestinal inflammation via regulation of the gut microbiota.

IL-36/IL-36R Signaling Promotes CD4+ T Cell-Dependent Colitis via Pro-Inflammatory Cytokine Production.

Inflammatory bowel disease (IBD) is a multifactorial, chronic disease that affects approximately 1.5 million people in the United States [1]. It presents with inflammation of the intestine with unknown etiology and its two main forms are Crohn's disease (CD) and ulcerative colitis (UC). Several important factors are implicated in the pathogenesis of IBD, one being dysregulation of the immune system resulting in the accumulation and stimulation of innate and adaptive immune cells and subsequent release of soluble factors, including pro-inflammatory cytokines. One of these cytokines is a member of the IL-36 cytokine family, IL-36γ, which is overexpressed in human IBD and experimental mouse models of colitis. In this study, we explored the role of IL-36γ in promoting CD4 + T cell activation and cytokine secretion. We found that IL-36γ stimulation of naïve CD4 + T cells significantly induced IFNγ expression in vitro and was associated with augmented intestinal inflammation in vivo using naive CD4 + cell transfer model of colitis. Using IFNγ-/- CD4 + cells, we observed a dramatic decrease in the ability of TNFα production and delayed colitis. This data not only suggests that IL-36γ is a master regulator of a pro-inflammatory cytokine network involving IFNγ and TNFα, but also highlights the importance of targeting IL-36γ and IFNγ as therapeutic approaches. Our studies have broad implications in relation to targeting specific cytokines in human IBD.

Monophosphoryl lipid A-adjuvanted nucleoprotein-neuraminidase nanoparticles improve immune protection against divergent influenza viruses.

Universal influenza vaccines are urgently needed to prevent recurrent influenza epidemics and inevitable pandemics. We generated double-layered protein nanoparticles incorporating two conserved influenza antigens-nucleoprotein and neuraminidase-through a two-step desolvation-crosslinking method. These protein nanoparticles displayed immunostimulatory properties to antigen-presenting cells by promoting inflammatory cytokine (IL-6 and TNF-α) secretion from JAWS II dendric cells. The nanoparticle immunization induced significant antigen-specific humoral and cellular responses, including antigen-binding and neutralizing antibodies, antibody- and cytokine (IFN-γ and IL-4)-secreting cells, and NP147-155 tetramer-specific cytotoxic T lymphocyte (CTL) responses. Co-administration of monophosphoryl lipid A (MPLA, a toll-like receptor 4 agonist) with the protein nanoparticles further improved immune responses and conferred heterologous and heterosubtypic influenza protection. The MPLA-adjuvanted nanoparticles reduced lung inflammation post-infection. The results demonstrated that the combination of MPLA and conserved protein nanoparticles could be developed into an improved universal influenza vaccine strategy.

Luminal bacteria coated with IgA and IgG during intestinal inflammation as a new and abundant stimulus for colonic macrophages.

In the gut, secretory immunoglobulin A is the predominant humoral response against commensals, although healthy hosts also produce microbiota-specific IgG antibodies. During intestinal inflammation, the content of IgG in the lumen increases along with the proportion of commensal bacteria coated with this antibody, suggesting signalling through the IgG-CD64 axis in the pathogenesis of inflammatory bowel diseases. In this work, we evaluated day by day the frequency of faecal bacteria coated with IgA and IgG during the development of DSS colitis. We studied the phenotype and phagocytic activity of F4/80+ CD64+ colonic macrophages, as well as the production of cytokines and nitric oxide by lamina propria or bone marrow-derived macrophages after stimulation with IgA+ , IgG+ and IgA+ IgG+ bacteria. We found that the percentage of faecal IgA+ IgG+ double-coated bacteria increased rapidly during DSS colitis. Also, analysis of the luminal content of mice with colitis showed a markedly superior ability to coat fresh bacteria. IgA+ IgG+ bacteria were the most potent stimulus for phagocytic activity involving CD64 and Dectin-1 receptors. IgA+ IgG+ bacteria observed during the development of DSS colitis could represent a new marker to monitor permeability and inflammatory progression. The interaction of IgA+ IgG+ bacteria with CD64+ F4/80+ macrophages could be part of the complex cascade of events in colitis. Interestingly, after stimulation, CD64+ colonic macrophages showed features similar to those of restorative macrophages that are relevant for tissue repair and healing.

Epithelial SMYD5 Exaggerates IBD by Down-regulating Mitochondrial Functions via Post-Translational Control of PGC-1α Stability.

BACKGROUND & AIMS: The expression and role of methyltransferase SET and MYND domain-containing protein 5 (SMYD5) in inflammatory bowel disease (IBD) is completely unknown. Here, we investigated the role and underlying mechanism of epithelial SMYD5 in IBD pathogenesis and progression. METHODS: The expression levels of SMYD5 and the mitochondrial transcriptional coactivator peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) were examined by Western blot, immunofluorescence staining, and immunohistochemistry in intestinal epithelial cells (IECs) and in colon tissues from human IBD patients and colitic mice. Mice with Smyd5 conditional knockout in IECs and littermate controls were subjected to dextran sulfate sodium-induced colitis and the disease severity was assessed. SMYD5-regulated mitochondrial biogenesis was examined by quantitative reverse-transcription polymerase chain reaction and transmission electron microscopy, and the mitochondrial oxygen consumption rate was measured in a Seahorse Analyzer system (Agilent, Santa Clara, CA). SMYD5 and PGC-1α interaction was determined by co-immunoprecipitation assay. PGC-1α degradation and turnover (half-life) were analyzed by cycloheximide chase assay. SMYD5-mediated PGC-1α methylation was assessed via in vitro methylation assay followed by mass spectrometry for identification of methylated lysine residues. RESULTS: Up-regulated SMYD5 and down-regulated PGC-1α were observed in intestinal epithelia from IBD patients and colitic mice. Smyd5 depletion in IECs protected mice from dextran sulfate sodium-induced colitis. SMYD5 was critically involved in regulating mitochondrial biology such as mitochondrial biogenesis, respiration, and apoptosis. Mechanistically, SMYD5 regulates mitochondrial functions in a PGC-1α-dependent manner. Furthermore, SMYD5 mediates lysine methylation of PGC-1α and subsequently facilitates its ubiquitination and degradation. CONCLUSIONS: SMYD5 attenuates mitochondrial functions in IECs and promotes IBD progression by enhancing PGC-1α degradation in a methylation-dependent manner. Strategies to decrease SMYD5 expression and/or increase PGC-1α expression in IECs might be a promising therapeutic approach to treat IBD patients.

Skin vaccination with dissolvable microneedle patches incorporating influenza neuraminidase and flagellin protein nanoparticles induces broad immune protection against multiple influenza viruses.

We generated self-adjuvanted protein nanoparticles of conserved influenza antigens and immunized mice via skin vaccination with dissolvable microneedle patches (MNPs) to increase the strength and breadth of immune responses. We produced M2e nanoparticles via ethanol desolvation, and double-layered NA1/M2e (shell/core), NA1-FliC/M2e, NA2/M2e, and NA2-FliC/M2e protein nanoparticles by chemically crosslinking influenza NA and flagellin (FliC) onto the surfaces of the M2e nanoparticles. The resulting nanoparticles retained FliC TLR5 innate signaling activity and significantly increased antigen-uptake and dendritic cell maturation in vitro. We incorporated the nanoparticles into MNPs for skin vaccination in mice. The nanoparticle MNPs significantly increased M2e and NA-specific antibody levels, the numbers of germinal center B cells, and IL-4 positive splenocytes. Double-layered nanoparticle MNP skin vaccination protected mice against homologous and heterosubtypic influenza viruses. Our results demonstrated that MNP skin vaccination of NA-FliC/M2e nanoparticles could be developed into a standalone or synergistic component of a universal influenza vaccine strategy.

IL-36 cytokines and gut immunity.

Interleukin 36 (IL-36) constitutes a group of cytokines that belong to the IL-1 superfamily. Emerging evidence has suggested a role of IL-36 in the pathogenesis of many inflammatory disorders. Intriguingly, in the gastrointestinal tract, IL-36 has a rather complex function. IL-36 receptor ligands are overexpressed in both animal colitis models and human IBD patients and may play both pathogenic and protective roles, depending on the context. IL-36 cytokines comprise three receptor agonists: IL-36α, IL-36ß and IL-36γ, and two receptor antagonists: IL-36Ra and IL-38. All IL-36 receptor agonists bind to the IL-36R complex and exert pleiotropic effects during inflammatory settings. Here, we first briefly review the processing and secretion of IL-36 cytokines. We then focus on the current understanding of the immunology effects of IL-36 in gut immunity. In addition, we also discuss the ongoing trials that aim to blockage IL-36R signalling for treating chronic intestinal inflammation and present some unexplored questions regarding IL-36 research.

Self and microbiota-derived epitopes induce CD4+ T cell anergy and conversion into CD4+Foxp3+ regulatory cells.

The physiological role of T cell anergy induction as a key mechanism supporting self-tolerance remains undefined, and natural antigens that induce anergy are largely unknown. In this report, we used TCR sequencing to show that the recruitment of CD4+CD44+Foxp3-CD73+FR4+ anergic (Tan) cells expands the CD4+Foxp3+ (Tregs) repertoire. Next, we report that blockade in peripherally-induced Tregs (pTregs) formation due to mutation in CNS1 region of Foxp3 or chronic exposure to a selecting self-peptide result in an accumulation of Tan cells. Finally, we show that microbial antigens from Akkermansia muciniphila commensal bacteria can induce anergy and drive conversion of naive CD4+CD44-Foxp3- T (Tn) cells to the Treg lineage. Overall, data presented here suggest that Tan induction helps the Treg repertoire to become optimally balanced to provide tolerance toward ubiquitous and microbiome-derived epitopes, improving host ability to avert systemic autoimmunity and intestinal inflammation.

IL-36R signaling integrates innate and adaptive immune-mediated protection against enteropathogenic bacteria.

Enteropathogenic bacterial infections are a global health issue associated with high mortality, particularly in developing countries. Efficient host protection against enteropathogenic bacterial infection is characterized by coordinated responses between immune and nonimmune cells. In response to infection in mice, innate immune cells are activated to produce interleukin (IL)-23 and IL-22, which promote antimicrobial peptide (AMP) production and bacterial clearance. IL-36 cytokines are proinflammatory IL-1 superfamily members, yet their role in enteropathogenic bacterial infection remains poorly defined. Using the enteric mouse pathogen, C.rodentium, we demonstrate that signaling via IL-36 receptor (IL-36R) orchestrates a crucial innate-adaptive immune link to control bacterial infection. IL-36R-deficient mice (Il1rl2-/- ) exhibited significant impairment in expression of IL-22 and AMPs, increased intestinal damage, and failed to contain C. rodentium compared to controls. These defects were associated with failure to induce IL-23 and IL-6, two key IL-22 inducers in the early and late phases of infection, respectively. Treatment of Il1rl2-/- mice with IL-23 during the early phase of C. rodentium infection rescued IL-22 production from group 3 innate lymphoid cells (ILCs), whereas IL-6 administration during the late phase rescued IL-22-mediated production from CD4+ T cell, and both treatments protected Il1rl2-/- mice from uncontained infection. Furthermore, IL-36R-mediated IL-22 production by CD4+ T cells was dependent upon NFκB-p65 and IL-6 expression in dendritic cells (DCs), as well as aryl hydrocarbon receptor (AhR) expression by CD4+ T cells. Collectively, these data demonstrate that the IL-36 signaling pathway integrates innate and adaptive immunity leading to host defense against enteropathogenic bacterial infection.

Internalization of Garlic-Derived Nanovesicles on Liver Cells is Triggered by Interaction With CD98.

The mechanism of how plant-derived nanovesicles are uptaken by cells remains unknown. In this study, the garlic-derived nanovesicles (GDVs) were isolated and digested with trypsin to remove all surface proteins. Digested GDVs showed less uptake compared to undigested GDVs, confirming that the surface proteins played a role in the endocytosis. On the cell side (HepG2), interestingly, blocking the CD98 receptors significantly reduced the uptake of GDVs. During the cellular internalization of GDVs, we observed that some surface proteins of GDVs were co-localized with CD98. A total lysate of the GDV surface showed a high presence of a mannose-specific binding protein, II lectin. Blocking GDV II lectin (using mannose preincubation) highly reduced the GDV internalization, which supports that direct interaction between II lectin and CD98 plays an important role in internalization. The GDVs also exhibited in vitro anti-inflammatory effect by downregulating proinflammatory factors on the HepG2 cells. This work contributes to understanding a part of the GDV internalization process and the cellular anti-inflammatory effects of garlic.

PTH induces bone loss via microbial-dependent expansion of intestinal TNF+ T cells and Th17 cells.

Bone loss is a frequent but not universal complication of hyperparathyroidism. Using antibiotic-treated or germ-free mice, we show that parathyroid hormone (PTH) only caused bone loss in mice whose microbiota was enriched by the Th17 cell-inducing taxa segmented filamentous bacteria (SFB). SFB+ microbiota enabled PTH to expand intestinal TNF+ T and Th17 cells and increase their S1P-receptor-1 mediated egress from the intestine and recruitment to the bone marrow (BM) that causes bone loss. CXCR3-mediated TNF+ T cell homing to the BM upregulated the Th17 chemoattractant CCL20, which recruited Th17 cells to the BM. This study reveals mechanisms for microbiota-mediated gut-bone crosstalk in mice models of hyperparathyroidism that may help predict its clinical course. Targeting the gut microbiota or T cell migration may represent therapeutic strategies for hyperparathyroidism.

Erythroid differentiation regulator-1 induced by microbiota in early life drives intestinal stem cell proliferation and regeneration.

Gut microbiota and their metabolites are instrumental in regulating intestinal homeostasis. However, early-life microbiota associated influences on intestinal development remain incompletely understood. Here we demonstrate that co-housing of germ-free (GF) mice with specific-pathogen free (SPF) mice at weaning (exGF) results in altered intestinal gene expression. Our results reveal that one highly differentially expressed gene, erythroid differentiation regulator-1 (Erdr1), is induced during development in SPF but not GF or exGF mice and localizes to Lgr5+ stem cells and transit amplifying (TA) cells. Erdr1 functions to induce Wnt signaling in epithelial cells, increase Lgr5+ stem cell expansion, and promote intestinal organoid growth. Additionally, Erdr1 accelerates scratch-wound closure in vitro, increases Lgr5+ intestinal stem cell regeneration following radiation-induced injury in vivo, and enhances recovery from dextran sodium sulfate (DSS)-induced colonic damage. Collectively, our findings indicate that early-life microbiota controls Erdr1-mediated intestinal epithelial proliferation and regeneration in response to mucosal damage.

"Western Diet"-Induced Adipose Inflammation Requires a Complex Gut Microbiota.

BACKGROUND & AIMS: Consumption of a low-fiber, high-fat, Western-style diet (WSD) induces adiposity and adipose inflammation characterized by increases in the M1:M2 macrophage ratio and proinflammatory cytokine expression, both of which contribute to WSD-induced metabolic syndrome. WSD-induced adipose inflammation might result from endoplasmic reticulum stress in lipid-overloaded adipocytes and/or dissemination of gut bacterial products, resulting in activation of innate immune signaling. Hence, we aimed to investigate the role of the gut microbiota, and its detection by innate immune signaling pathways, in WSD-induced adipose inflammation. METHODS: Mice were fed grain-based chow or a WSD for 8 weeks, assessed metabolically, and intestinal and adipose tissue were analyzed by flow cytometry and quantitative reverse transcription polymerase chain reaction. Microbiota was ablated via antibiotics and use of gnotobiotic mice that completely lacked microbiota (germ-free mice) or had a low-complexity microbiota (altered Schaedler flora). Innate immune signaling was ablated by genetic deletion of Toll-like receptor signaling adaptor myeloid differentiation primary response 88. RESULTS: Ablation of microbiota via antibiotic, germ-free, or altered Schaedler flora approaches did not significantly impact WSD-induced adiposity, yet dramatically reduced WSD-induced adipose inflammation as assessed by macrophage populations and cytokine expression. Microbiota ablation also prevented colonic neutrophil and CD103- dendritic cell infiltration. Such reduced indices of inflammation correlated with protection against WSD-induced dysglycemia, hypercholesterolemia, and liver dysfunction. Genetic deletion of myeloid differentiation primary response 88 also prevented WSD-induced adipose inflammation. CONCLUSIONS: These results indicate that adipose inflammation, and some aspects of metabolic syndrome, are not purely a consequence of diet-induced adiposity per se but, rather, may require disturbance of intestine-microbiota interactions and subsequent activation of innate immunity.

Combined IL-2 Immunocomplex and Anti-IL-5 mAb Treatment Expands Foxp3+ Treg Cells in the Absence of Eosinophilia and Ameliorates Experimental Colitis.

Interleukin (IL)-2 is expressed during T cell activation and induces the proliferation and differentiation of T cells. CD4+Foxp3+ regulatory T cells (Tregs) constitutively express the high affinity IL-2 receptor (CD25/IL-2Rα) and rapidly respond to IL-2 to elaborate numerous suppressive mechanisms that limit immune-mediated pathologies. Accumulating evidence supports the concept that an aberrant balance between Tregs and Teff contribute to the pathology of intestinal inflammation and that the IL-2/Treg axis is a potential pathway to exploit for the treatment of inflammatory bowel disease (IBD). Here, we show that treatment of mice with IL-2/IL-2 antibody (JES6-1) immunocomplex during DSS-induced colitis induced Foxp3+ Treg expansion, but also potently stimulated GATA3+ type 2 innate lymphoid cell (ILC2) proliferation and high-level expression of IL-5. Furthermore, IL-2/JES6-1 treatment resulted in massive eosinophil accumulation and activation in the inflamed colon, and afforded only modest protection from colitis. In light of these findings, we observed that combined IL-2/JES6-1 and anti-IL-5 mAb treatment was most effective at ameliorating DSS-induced colitis compared to either treatment alone and that this regimen allowed for Foxp3+ Treg expansion without concomitant eosinophilia. Collectively, our findings provide insight into how blockade of IL-5 may aid in optimizing IL-2 immunotherapy for the treatment of intestinal inflammation.

Macrophage-dependent neutrophil recruitment is impaired under conditions of increased intestinal permeability in JAM-A-deficient mice.

Junctional adhesion molecule-A (JAM-A) is a transmembrane glycoprotein expressed on leukocytes, endothelia, and epithelia that regulates biological processes including barrier function and immune responses. While JAM-A has been reported to facilitate tissue infiltration of leukocytes under inflammatory conditions, the contributions of leukocyte-expressed JAM-A in vivo remain unresolved. We investigated the role of leukocyte-expressed JAM-A in acute peritonitis induced by zymosan, lipopolysaccharide (LPS), or TNFα using mice with selective loss of JAM-A in myelomonocytic cells (LysM-Cre;Jam-afl/fl). Surprisingly, in LysM-Cre;Jam-afl/fl mice, loss of JAM-A did not affect neutrophil (PMN) recruitment into the peritoneum in response to zymosan, LPS, or TNFα although it was significantly reduced in Jam-aKO mice. In parallel, Jam-aKO peritoneal macrophages exhibited diminished CXCL1 chemokine production and decreased activation of NF-kB, whereas those from LysM-Cre;Jam-afl/fl mice were unaffected. Using Villin-Cre;Jam-afl/fl mice, targeted loss of JAM-A on intestinal epithelial cells resulted in increased intestinal permeability along with reduced peritoneal PMN migration as well as lower levels of CXCL1 and active NF-kB similar to that observed in Jam-aKO animals. Interestingly, in germ-free Villin-Cre;Jam-afl/fl mice, PMN recruitment was unaffected suggesting dependence on gut microbiota. Such observations highlight the functional link between a leaky gut and regulation of innate immune responses.

Early-Life Microbiota Exposure Restricts Myeloid-Derived Suppressor Cell-Driven Colonic Tumorigenesis.

Gut microbiota and their metabolites are instrumental in regulating homeostasis at intestinal and extraintestinal sites. However, the complex effects of prenatal and early postnatal microbial exposure on adult health and disease outcomes remain incompletely understood. Here, we showed that mice raised under germ-free conditions until weaning and then transferred to specific pathogen-free (SPF) conditions harbored altered microbiota composition, augmented inflammatory cytokine and chemokine expression, and were hyper-susceptible to colitis-associated tumorigenesis later in adulthood. Increased number and size of colon tumors and intestinal epithelial cell proliferation in recolonized germ-free mice were associated with augmented intratumoral CXCL1, CXCL2, and CXCL5 expression and granulocytic myeloid-derived suppressor cell (G-MDSC) accumulation. Consistent with these findings, CXCR2 neutralization in recolonized germ-free mice completely reversed the exacerbated susceptibility to colitis-associated tumorigenesis. Collectively, our findings highlight a crucial role for early-life microbial exposure in establishing intestinal homeostasis that restrains colon cancer in adulthood.

Autotaxin determines colitis severity in mice and is secreted by B cells in the colon.

Autotaxin (ATX or ENPP2) is a secreted lysophospholipase D that produces lysophosphatidic acid (LPA), a pleiotropic lipid mediator acting on specific GPCRs. ATX and LPA have been implicated in key (patho)physiologic processes, including embryonic development, lymphocyte homing, inflammation, and cancer progression. Using LPA receptor knockout mice, we previously uncovered a role for LPA signaling in promoting colitis and colorectal cancer. Here, we examined the role of ATX in experimental colitis through inducible deletion of Enpp2 in adult mice. ATX expression was increased upon induction of colitis, whereas ATX deletion reduced the severity of inflammation in both acute and chronic colitis, accompanied by transient weight loss. ATX expression in lymphocytes was strongly reduced in Rag1-/- and µMT mice, suggesting B cells as a major ATX-producing source, which was validated by immunofluorescence and biochemical analyses. ATX secretion by B cells from control, but not Enpp2 knockout, mice led to ERK activation in colorectal cancer cells and promoted T cell migration. We conclude that ATX deletion suppresses experimental colitis and that B cells are a major source of ATX in the colon. Our study suggests that pharmacological inhibition of ATX could be a therapeutic strategy in colitis.-Lin, S., Haque, A., Raeman, R., Guo, L., He, P., Denning, T. L., El-Rayes, B., Moolenaar, W. H., Yun, C. C. Autotaxin determines colitis severity in mice and is secreted by B cells in the colon.

IL-36γ Protects against Severe Influenza Infection by Promoting Lung Alveolar Macrophage Survival and Limiting Viral Replication.

Although influenza virus infection remains a concerning disease for public health, the roles of individual cytokines during the immune response to influenza infection are not fully understood. We have identified IL-36γ as a key mediator of immune protection during both high- and low-pathogenesis influenza infection. Il36g mRNA is upregulated in the lung following influenza infection, and mice lacking IL-36γ have greatly increased morbidity and mortality upon infection with either H1N1 or H3N2 influenza. The increased severity of influenza infection in IL-36γ-knockout (KO) mice is associated with increased viral titers, higher levels of proinflammatory cytokines early in infection, and more diffuse pathologic conditions late in the disease course. Interestingly, the increased severity of disease in IL-36γ-KO mice correlates with a rapid loss of alveolar macrophages following infection. We find that the alveolar macrophages from naive IL-36γ-KO mice have higher expression of M2-like surface markers compared with wild-type (WT) mice and show increased apoptosis within 24 h of infection. Finally, transfer of WT alveolar macrophages to IL-36γ-KO mice restores protection against lethal influenza challenge to levels observed in WT mice. Together, these data identify a critical role for IL-36γ in immunity against influenza virus and demonstrate the importance of IL-36γ signaling for alveolar macrophage survival during infection.