Mucosal Immunology

Intraepithelial lymphocytes expressing the {gamma}{delta} T cell receptor ({gamma}{delta} IEL) continuously survey the intestinal epithelium to promote mucosal host defense. Although {gamma}{delta} IELs migrate in and out of the lateral intercellular space (LIS) between adjacent enterocytes, the molecular mechanisms governing their migratory behavior are incompletely understood. Based on the known role of CD47, or integrin associated protein (IAP), in mediating neutrophil transepithelial migration, we investigated whether CD47 expression reflects a conserved mechanism regulating {gamma}{delta} IEL surveillance behavior. Here, we report that conditional CD47 deletion on intestinal epithelial cells or {gamma}{delta} T cells had no effect on IEL composition. Using intravital imaging, we identified complementary roles for CD47 on {gamma}{delta} IELs and epithelial cells, with epithelial CD47 restricting {gamma}{delta} IEL motility and {gamma}{delta} T-cell-derived CD47 promoting cell migration. Further investigation revealed that both CD47 and CD18 contribute to {gamma}{delta} IEL surveillance behavior, although CD47 regulates {gamma}{delta} IEL migration in a CD18-independent manner.

Background: Patients receiving anti-TNF treatment for chronic inflammatory disease display impaired antibody responses, but it remains unclear how immune memory formation is affected. We evaluated antibody responses and memory B cells (Bmem) after COVID-19 booster vaccination in inflammatory bowel disease (IBD) patients receiving anti-TNF treatment. Methodology: Blood was sampled at baseline, 1, and 6 months after WH1/BA.5 bivalent or XBB.1.5 monovalent vaccination from 27 IBD patients receiving intravenous anti-TNF and 44 controls. Neutralizing antibodies were measured using an infectious virus assay. SARS-CoV-2 spike receptor binding domain (RBD)-specific serum IgG was quantified by ELISA, and RBD-specific Bmem were immunophenotyped by flow cytometry using recombinant proteins from ancestral, Omicron BA.1, BA.5, XBB.1.5, and JN.1 variants. Results: Serum IgG to vaccine RBD and neutralizing antibodies in patients increased pre to 1 month post-vaccination, but were lower than controls. Ancestral-, BA.5- and XBB.1.5-specific Bmem increased after vaccination but were significantly lower in patients than controls. Within RBD-specific Bmem, frequencies of recently activated CD21lo cells were increased after vaccination, and were higher in patients than controls. Fewer antigen-specific Bmem in patients expressed IgG4, and more expressed IgG3 or IgD following vaccination. Following vaccination, more RBD-specific Bmem recognized multiple viral variants. However, patients had fewer Bmem that could bind to subvariants than controls. Conclusion: Antibody and Bmem responses to COVID-19 booster vaccination in anti-TNF-treated IBD patients displayed reduced capacity, durability and cross-reactivity, suggesting impaired immune memory for protection against breakthrough infection. This supports the recommendation for annual booster vaccination to prevent severe disease and viral spread.

Group 2 innate lymphoid cells (ILC2s) regulate type 2 immune responses partly by recruiting eosinophils, but the mechanisms underlying this process remain incompletely understood. Although both ILC2s and type 2 T helper (Th2) cells are capable of expressing IL-5, a cytokine critical for recruiting eosinophils, ILC2s are more potent than Th2 cells in this process. Here, we show that the transcription factor Bhlhe40 promotes GM-CSF production in ILC2s, and Bhlhe40 expression in ILC2s is required for efficient eosinophil recruitment during both papain- and helminth-induced type 2 immune responses. However, Bhlhe40 deficiency in ILC2s had no effect on the production of classical type 2 cytokines, including IL-4, IL-5 and IL-13, despite Bhlhe40 being required for type 2 cytokine production by Th2 cells. Furthermore, in contrast to ILC2s, Th2 cells produced little GM-CSF and administration of GM-CSF rescued eosinophil recruitment in ILC2-specific Bhlhe40-deficient mice. In addition to promoting GM-CSF expression, Bhlhe40 repressed IL-10 production in ILC2s as it did in Th2 cells, particularly during chronic inflammation. Single-cell transcriptomic analyses further supported this regulatory network, and the ChIP-Seq data revealed direct binding of Bhlhe40 to the enhancer and promoter regions within the Il10 and Csf2 loci. Collectively, our findings show that Bhlhe40 exerts distinct gene regulatory functions in ILC2s and Th2 cells, and Bhlhe40 modulates the inflammatory and anti-inflammatory functions of ILC2s by promoting GM-CSF while suppressing IL-10 production.

Substantial inter-individual variation in susceptibility to viral infection persists despite widespread vaccination, and its immunological basis remains poorly understood. We investigated how innate and adaptive immune responses contribute to susceptibility to SARS-CoV-2 infection during the early COVID-19 pandemic. We compared two groups of vaccinated individuals who either remained uninfected or became infected during the first Omicron wave. Blood samples were collected at baseline and 24 weeks later. Peripheral blood mononuclear cells (PBMCs) and polymorphonuclear neutrophils (PMNs) were isolated and stimulated with the TLR7/8 agonist R848 to assess innate responses. PBMCs were stimulated with SARS-CoV-2 peptide pools and highly purified inactivated viruses (ancestral and Omicron BA.1) to evaluate adaptive immunity. Prior to infection, individuals in the infected group exhibited reduced CD4 and CD8 T cells proliferative responses, alongside with increased TNF production across all stimulation conditions, despite largely comparable immune phenotypes, indicating a pre-existing functional immune deficit. Following infection, T-cell proliferation and IFN-gamma production were partially restored in response to viral antigens, although responses to Omicron BA.1 remained suboptimal. This functional deficit was accompanied by heightened inflammatory activity, including increased TNF and IFN-gamma production, elevated anti-nucleocapsid IgG3 levels, higher frequencies of B cells and myeloid cells, reduced circulating interferon-inducible T-cell Alpha Chemoattractant (I-TAC) concentrations, and a modest impairment in PMN IL-8 responses. Notably, these alterations were detectable prior to infection and persisted thereafter, indicating that they represent determinants rather than consequences of viral infection. Importantly, beyond differences in the magnitude of immune responses, protection was associated with the degree of functional coordination within the humoral compartment, as reflected by the relationship between Spike-binding antibodies and neutralizing activity. Together, these results demonstrate that susceptibility to Omicron infection is linked to a pre-existing and persistent functional immune imbalance affecting both innate and adaptive arms of immunity.

Interactions between intraepithelial lymphocytes (IELs) and the intestinal epithelium are central to mucosal homeostasis and disease. However, mechanistic in vitro studies describing their crosstalk in humans are limited by scarceness of primary material and insufficient knowledge about co-culture requirements. Here, we establish an autologous human duodenal IEL-organoid co-culture system encompassing expandable and bankable IEL and organoid protocols, with co-culture conditions that allow viability of both cell types. This system enables successive interrogation of lympho-epithelial interactions starting from minimal biopsy material. Under baseline conditions, CD45CD8CD103TCR{beta} IELs retain tissue-residency and effector features and induce an epithelial interferon response and chemokine production, without overt epithelial apoptosis. IL-15 and IL-21, essential cytokines involved in IEL-activation in intestinal enteropathies like celiac disease, increases granzyme B expression and interferon-{gamma} secretion but do not trigger epithelial cell death. However, enforcing IEL-epithelial contact using an anti-CD3-anti-Ep-CAM bispecific antibody induces epithelial apoptosis accompanied by increased tumor necrosis factor (TNF) and FAS-ligand (FASLG) secretion. These findings validate the platforms ability to resolve non-destructive and cytotoxic lympho-epithelial interaction and provide a tractable system for studying intestinal inflammation and immune-mediated epithelial cell death.

Inflammatory bowel disease (IBD) often involves disrupted intestinal epithelial barrier, but therapies specifically targeting this barrier are limited. We found that downregulated AUF1 (HNRNPD) contributes to defective barrier integrity in ulcerative colitis (UC). Compared to controls, its expression level was decreased and inversely correlated with clinical severity. Knocking down AUF1 in human and mouse colonic organoids led to impaired barrier function, with reduced Occludin and upregulated Claudin-2, mimicking characteristic IBD-associated mucosal alterations. Distinct RNA-binding activity of AUF1 protein isoforms contributed to these changes: p37 stabilized Occludin mRNA and blocked microRNA-122/Ago2-mediated repression, whereas p40 promoted Claudin-2 mRNA degradation via ubiquitin-proteasome pathway. Restoring AUF1 expression in organoids enhanced epithelial properties and, when transplanted into mice with established colitis, accelerated mucosal healing and epithelial regeneration in recipient mice and decreased fibrosis. Our study unravelled a post-transcriptional mechanism important for intestinal homeostasis and demonstrated a concept of using engineered organoids for treating IBD.

Protective immunity against many infectious diseases develops following primary infection, called infection induced immunity (III), and provides a blueprint for vaccination. However, many vaccination strategies have failed. In the parasitic Leishmania major model of self-healing cutaneous disease, control of secondary challenge infection relies on pre-existing T helper (Th)1-dependent activation of skin-infiltrating monocytes for elimination of intracellular parasites. To better understand immune-evasion of pre-existing Th1 immunity by pathogens, we investigated the pathogen-niche established following non-healing challenge infection with the L. amazonensis parasite in a setting of pre-existing III. Following secondary challenge, pre-existing Th1 III initially controlled infection but ultimately failed. Loss of protection was not overtly STAT6- or IL-10-mediated. Rather, monocyte-lineage tracing revealed inflammatory monocyte-derived PD-L1+PD-L2+ macrophages provide an intracellular pathogen-niche and facilitate evasion of pre-existing Th1 immunity. Anti-PD-1 immune checkpoint blockade enhanced uninfected, but not infected, monocyte-derived cell activation and depletion of monocyte-derived precursors improved parasite control. These observations suggest that evasion of pre-existing Th1 immunity in this setting is not due to a failure of the Th1 response, but rather due to infected-cell intrinsic defects in activation.

Ulcerative colitis (UC) is characterised by chronic colonic inflammation with marked heterogeneity in disease severity and therapeutic outcomes. Here, we define a spatially organised, polyfunctional cytotoxic CD4 T-cell state associated with mucosal inflammation and adverse therapeutic outcomes in UC. Integrating ex vivo T-cell receptor stimulation with multi-cohort bulk and single-cell transcriptomics and multiparameter flow cytometry, we show that GZMB CD4 T cells are preferentially enriched in inflamed UC mucosa, but not peripheral blood, and co-express cytotoxic molecules, Th1- and Th17-associated cytokines and chemokines, and immunoregulatory receptors. Single-cell analyses implicate inflammatory cytokine and antigen-presentation signals in the acquisition or maintenance of this state. High-resolution spatial profiling localised this programme predominantly to Th17 cells, which were preferentially enriched within multicellular inflammatory and tertiary lymphoid structure-associated niches. Across independent patient cohorts, a transcriptional signature derived from this state increased with endoscopic disease severity and was associated with reduced response to anti-TNF and anti-IL-12/23p40 therapies. Adoptive transfer of Gzma/Gzmb-deficient rather than wild-type CD4 T cells into Rag2-deficient recipient mice markedly attenuated experimental colitis and abrogated the polyfunctional cytokine phenotype, demonstrating that granzyme-dependent effector activity is a key mechanism driving CD4+ T-cell-mediated intestinal inflammation. Finally, human host-microbiome analysis linked this programme to intestinal dysbiosis, while transfer of dysbiotic microbiota promoted the emergence of a corresponding state in vivo. Collectively, these findings define a microbiota-responsive, spatially organised polyfunctional cytotoxic CD4 T-cell programme that contributes to intestinal inflammation and is associated with disease severity and treatment resistance in UC.

The longstanding association between psychological trauma or stress and subsequent chronic inflammatory disorders is well-documented, but the mechanism by which psychopathology causes these immune changes has yet to be elucidated. We have previously reported that sympathetic innervation to lymphoid organs and beta adrenergic receptor signaling are essential for T-lymphocyte interleukin 17A (IL-17A) production and TH17 polarization, though the exact mechanistic contribution of this signaling to the development of TH17 cells remained unclear. Therefore, we hypothesized that norepinephrine (NE) is a novel and direct regulator of T-lymphocyte IL-17A expression. Herein, we indeed observed that NE regulates baseline IL-17A in vivo. We further identified a novel mechanism by which transforming growth factor beta (TGF{beta}) and NE together result in TH17 polarization and IL-17A production in CD4+ T-lymphocytes. Additionally, we found that cAMP, PKA, and CREB are induced by NE signaling, which ultimately increases CBP/p300 activity to initiate ROR{gamma}t transcription. Surprisingly, our data also demonstrate that STAT3, a transcription factor previously described as necessary for canonical TH17 polarization, is not involved in this novel pathway and may even be downregulated. Combined with bulk RNA sequencing data, our data highlight robust differences between the novel and canonical pathways to TH17 polarization. Altogether, our data reveal a novel, noncanonical mechanism that links sympathetic nervous system activity with IL-17A related inflammation, which may have significant relevance to sympathoexcitation-related disorders that stem from psychological trauma or stress.

Chronic inflammation disrupts hormonal balance in the Hypothalamic-Pituitary-Gonadal (HPG) axis, contributing to reproductive disorders. While immune cells in the hypothalamus and ovaries have been extensively studied, their impact on the pituitary remains largely unexplored. Our research identifies pituitary macrophages (PitMacs) as the dominant pituitary immune cell population with a role in regulating reproductive gonadotropin secretion both in vitro and in vivo. Using a targeted AAV-based depletion strategy, we demonstrate that a reduction of PitMacs decreases serum gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), in female mice. PitMacs are transcriptomically distinct from other tissue-resident macrophages and harbor a unique translational program that reflects the pituitarys endocrine identity, including active translation of growth hormone (Gh) and prolactin (Prl). Cytokine profiling identified CXCL5 and IFN-{gamma} as key PitMac-derived mediators of gonadotropin regulation. Mechanistically, CXCL5 signals through CXCR2 to activate the MAPK pathway, converging with Gonadotropin-Releasing Hormone (GnRH) signaling in a time-dependent manner to regulate LH secretion and GnRH receptor surface expression. These findings establish PitMacs as essential endocrine-immune integrators, opening new avenues for understanding inflammation-driven reproductive disorders. One Sentence SummaryPituitary macrophages are unique hormone-producing immune cells that regulate hormone secretion via cytokine signaling.

Seeking a simple vaccine to protect against all cancer-associated human papillomaviruses (HPV), L2 residues 17-36 of both HPV16 and HPV31 displayed on the surface of an Adeno-Associated Virus-Like Particle (AAVLP-HPV) was developed. Here, a phase 1 randomized, placebo-controlled, double-blind clinical study has been conducted in 20 male and female subjects at a single dose level (20 ug) without an adjuvant. AAVLP-HPV vaccine administration was safe and well tolerated. Repeat vaccination with AAVLP-HPV elicited L2-specific neutralizing antibodies of modest titer in serum. Antibodies cross-reactive with L2 of diverse HPV types were detected, but responses were weak in most vaccinees. We conclude that while AAVLP-HPV vaccination is well tolerated, an adjuvant is likely needed to consistently elicit durable and broadly neutralizing responses.

Objective: Lymphatic dysfunction has been implicated in exacerbating fibrosis in numerous diseases, yet the role of the lymphatic system in laryngotracheal injury has not previously been explored. This study aims to evaluate lymphatic vascular remodeling in a murine model of laryngotracheal stenosis (LTS) and determine how pharmacologic blockade of lymphangiogenesis impacts airway healing after mucosal injury. Methods: LTS was induced in C57BL6 mice using an established chemomechanical injury model. Lymphatic density was quantified using LYVE-1 immunohistochemistry. Mice were treated with the VEGFR-3-selective tyrosine kinase inhibitor SAR131675 to block lymphangiogenesis after injury. Outcomes assessed included survival, histopathology, immunohistochemistry, and Evans blue dye vascular leakage. Results: Laryngotracheal injury induced a substantial increase in subepithelial lymphatic vessel density concomitant with fibrotic remodeling. Pharmacologic inhibition of VEGFR-3 signaling with SAR131675 abrogated this lymphangiogenic response and resulted in markedly increased mortality, impaired epithelial repair with obstructive sloughing, increased edema, and persistent histopathologic evidence of tissue injury. A qualitative increase in pathologic fibrocellular remodeling was also observed, though with no measurable difference in lamina propria thickness. Conclusion: These findings establish lymphatic remodeling as an essential component of successful airway repair following mucosal injury. Lymphatic dysfunction is a common feature of known risk factors for LTS including diabetes, obesity, and prematurity, and can be exacerbated by positive pressure ventilation. Disruption of the lymphangiogenic response to airway injury may lead to stasis of pro-inflammatory factors that result in chronic inflammation, maladaptive remodeling, and pathologic tissue changes. The lymphatic vasculature is a viable target for future mechanistic study and potential therapeutic intervention following airway injury.

Despite immunosuppressive regimens targeting adaptive immunity, chronic lung allograft dysfunction (CLAD) remains the major obstacle to durable lung allograft survival. Here, we identify colony-stimulating factor 1 receptor (CSF1R)-expressing interstitial macrophages as critical orchestrators of CLAD. Using lung tissue from patients with CLAD and a mouse model of mismatched lung transplantation, we show that both donor-derived tissue-resident and recipient- monocyte-derived interstitial macrophages spatially co-localize within peribronchial immune aggregates in patients with CLAD. These interstitial macrophages express distinct cytokine programs that include those implicated in the recruitment of T and B cells. Pharmacological inhibition of CSF1R after lung transplantation in mice reduced interstitial macrophage abundance and attenuated CLAD pathology. Our findings identify donor- and recipient-derived interstitial macrophages as upstream regulators of CLAD and suggest CSF1R as a therapeutic target for its prevention and treatment.

Inflammatory bowel disease (IBD) is a heterogeneous chronic disease driven by dysregulated mucosal immunity and impaired epithelial barrier function. Although biologics have improved disease management, they are frequently associated with systemic immunosuppression and adverse effects, highlighting the need for localized therapeutic strategies that both control inflammation and promote tissue repair. Here, we developed a protein bispecific termed 7A2-IgG4-IL22, composed of a human IgG4-Fc domain displaying an antagonistic anti-human MAdCAM-1 single chain (sc)-Fv and a human interleukin (IL-)22. The anti-MAdCAM-1 scFv retained the functional activity of the parental monoclonal antibody, inhibiting T cell activation, expansion and differentiation from naive precursors. Blockade of the MAdCAM-1 signaling axis also reduced production of pro-inflammatory cytokines relevant to IBD pathogenesis, including IFN{gamma} and TNF. On the epithelial side, the IL-22 cargo induces robust signaling in epithelial cells, promoting the expression of IL-22 response genes associated with antimicrobial defense, mucosal homeostasis, as well as IL-10 and CXCL1 expression. This effect contributes to immune cell trafficking to the intestinal mucosa. Together, this bispecific provides a localized dual-mechanism strategy for restoring intestinal immune homeostasis.

Maintaining brain homeostasis is crucial for proper function of the central nervous system and has traditionally been attributed to neuronal and glial interactions. However, recent research highlights the essential role of brain-resident immune cells in this process. Our study characterizes brain-specific CD8+ T cells and elucidates their significant contribution to brain homeostasis and behavior. We identified a distinct population of CD8+ T cells that infiltrates the brain during early development, undergoes clonal expansion, and acquires effector memory-like characteristics through interactions with microglia. Notably, the absence of these cells results in hyperactivation of neuronal activity and abnormal behaviors, due to loss of regulation of interferon-gamma (IFN-{gamma}) secreted by CD8+ T cells. Our findings demonstrate that IFN-{gamma} secreting brain-specific CD8+ T cells are crucial for maintaining the physiological level of neuronal excitability and normal behavioral patterns. This study provides novel insights into neuroimmune interactions, emphasizing the critical role of CD8+ T cells in sustaining brain function and behavior.

Hirschsprung disease (HSCR) is a severe birth defect where ganglia of the enteric nervous system (ENS) are missing from distal bowel. The aganglionic segment is also characterized by increased epithelial permeability and pro-inflammatory immune activation. These problems may sequentially lead to translocation of gut microbes into the colon wall and systemic circulation, resulting in enterocolitis and sepsis. Current HSCR treatment via surgical resection of the aganglionic segment is lifesaving but not curative, often leaving patients with persistent gastrointestinal complications including recurrent risk of enterocolitis. As alternative, we are developing a regenerative medicine strategy based on in situ stimulation of tissue-resident ENS progenitors via rectal administration of the neurotrophic factor GDNF. Here, we report that GDNF-based therapy has pleiotropic gastrointestinal effects in a mouse model of short-segment HSCR, beyond its role in ENS regeneration. Interestingly, we found that these protective effects are not restricted to the aganglionic distal colon, also positively impacting the ENS-containing proximal colon. GDNF treatment reduces bacterial translocation both locally and in peripheral organs, and this is associated with recovery of the key epithelial junction proteins CLDN3, ZO1 and DSG2. Furthermore, multiparameter flow cytometry-based analysis of 55 lymphoid and 17 myeloid cell subtypes revealed that GDNF treatment has global anti-inflammatory effects, preferentially affecting innate over adaptive immunity. Overall, these findings highlight a critical role for GDNF treatment in reestablishing proper epithelial and immune cell homeostasis, offering promising therapeutic avenues not only for HSCR but also potentially for other intestinal disorders with overlapping pathophysiology.

The mechanisms underlying the progression of pulmonary fibrosis in idiopathic pulmonary fibrosis (IPF) and other interstitial lung diseases remain unclear. Increased extracellular matrix stiffness is a hallmark of fibrotic lung diseases. Monocyte-derived macrophages can promote fibrosis progression. However, there is limited understanding of how the mechanical properties of the fibrotic microenvironment influence macrophage phenotypes. Profibrotic macrophages are apoptosis-resistant, and this phenotype is modulated by enhanced mitochondrial bioenergetics. The objective of the study was to determine how lung tissue stiffness impacts macrophage phenotypes and fibrotic progression. We demonstrate that mechanoactivated macrophages exhibit apoptosis-resistance, increased expression of the antiapoptotic protein Bcl-xL and increased mitochondrial oxidative phosphorylation. Critically, the metabolic reprogramming observed in mechanoactivated macrophages is dependent on increased glutaminolysis. Inhibition of glutaminolysis attenuated apoptosis resistance in mechanoactivated macrophages. Moreover, inhibition of Bcl-xL in vivo protected mice against experimental pulmonary fibrosis. Lastly, mechanoactivated primary IPF macrophages produce more profibrotic cytokines and promote extracellular matrix production in precision-cut lung slices. We describe a mechanism for acquired macrophage apoptosis resistance dependent on metabolic reprogramming regulated by extracellular matrix stiffness. Our results identify mechanoactivated apoptosis-resistant macrophages as pro-fibrotic mediators, suggesting a novel therapeutic target in IPF and related fibrotic disorders.

Regulatory T (Treg) cells expressing ROR{gamma}t accumulate in the intestinal mucosa, yet the signals that determine whether they remain suppressive or acquire inflammatory features are incompletely defined. We first reanalyzed human ileal single-cell data and identified Crohns disease-enriched FOXP3 states in which RORC, HIF1A, hypoxia-responsive, inflammatory, and metabolic programs converged. We then deleted Hif1a in ROR{gamma}t-expressing cells and tested acute DSS colitis, T cell transfer colitis, and azoxymethane/DSS-induced colitis-associated colorectal cancer (CAC). {Delta}Hif1a mice were protected in all three settings. In lymphopenic recipients given the same pathogenic naive T cells, changing only the genotype of the cotransferred Treg population enhanced protection, linking the phenotype to regulatory-cell function in vivo. Reanalysis of mouse colonic Treg single-cell ATAC-seq nominated suppressive and mitochondrial programs for cell-intrinsic testing during low HIF1- expression. {Delta}Hif1a ROR{gamma}t Treg produced more IL-10 and less IL-17A and IFN-{gamma}, limited responder-cell proliferation, contained fewer dysfunctional and mitochondrial-reactive-oxygen-species-high mitochondria, favored fusion-associated transcription, and displayed greater basal and maximal oxygen consumption and reserve capacity. During CAC, HIF-1 loss blunted inflammatory ROR{gamma}t Treg accumulation and reduced tumor burden. Human trajectory and gene-regulatory-network analyses further predicted that HIF1A perturbation would oppose selected disease-associated branches. Together, these findings identify HIF-1 as a context-dependent checkpoint that connects hypoxia-responsive transcription to mitochondrial fitness and inflammatory plasticity in intestinal ROR{gamma}t Treg.

Legionella pneumophila (L. pneumophila) is the causative agent of Legionnaires' disease, a severe bacterial pneumonia. Difficulty in diagnosing Legionnaires' disease leads to an underreporting of cases and delayed treatment. Rapid-acting, broad-spectrum therapies are needed to treat pathology while avoiding antibiotic resistance. We showed that gelsolin knockout (gsn-/-) mice succumb more quickly to severe L. pneumophila infection despite no difference in bacterial loads in the lung compared to wild type mice. There is an increase in CXCL1/KC production from macrophages from gsn-/- mice, which is accompanied by increased neutrophils and apoptosis in their lungs. Neutrophils lacking gelsolin produce fewer neutrophil extracellular traps, and their mitochondrial capacity is diminished in response to L. pneumophila. Gelsolin is required for maintaining mitochondrial network morphology and respiration in L. pneumophila infected macrophages. When given recombinant gelsolin protein, gsn-/- mice survive significantly longer during severe L. pneumophila infection, with reduced lung pathology, and the inflammatory signature of their macrophages was reduced in vitro. Together, gelsolin protects mice during severe L. pneumophila infection, dampens inflammation, promotes mitochondrial health, and maintains neutrophil function.

Enteric infections caused by Salmonella enterica remain a major global health concern and are increasingly associated with antimicrobial resistance. Therefore, new strategies to combat this important pathogen are needed. The interactions between S. enterica and the human host have been the subject of intense investigation over the last several decades, yet new findings continue to emerge. We previously showed that 15-deoxy-{Delta}12,14-prostaglandin J2 (15d-PGJ2) reduces Salmonella colonization of macrophages, but the mechanisms underlying this protective effect were still unknown. Here, we demonstrate that 15d-PGJ2 limits Salmonella infection by suppressing TLR4 signaling and inflammasome activation. Treatment with 15d-PGJ2 reduced TLR4 expression, NF-{kappa}B activation, iNOS, COX-2, nitric oxide production, IL-1{beta} release, and inflammasome-related targets, including NLRP3 and caspase-1 activity, while only partially reversing macrophage polarization. Combined treatment with the TLR4 antagonist TAK-242 further reduced bacterial colonization of and IL-1{beta} release by macrophages, supporting the involvement of TLR4 signaling in the effects of 15d-PGJ2. During mouse infections, 15d-PGJ2 reduced bacterial burdens in a tissue-dependent manner. Together, these findings demonstrate that 15d-PGJ2 limits Salmonella infection through selective modulation of TLR4 signaling and inflammasome activation.