The host response to commensal and pathogenic bacteria has been extensively characterized using human cancer cell line models but remains less defined in primary intestinal cellular systems. Recent evidence has demonstrated that mice lacking the Nod-like receptor (NLR) protein NLRC4 are susceptible to Shigella flexneri infection and thus represent a new model to study the mechanistic aspects of S. flexneri-host interaction. Using ileal organoids from wild-type (WT) and Nlrc4-/- mice, we first confirmed that NLRC4 was required for the restriction of intracellular S. flexneri growth. Surprisingly, NLRC4 further mediated the detection of bacteria-free S. flexneri supernatants, suggesting that ileal organoids sample proteins from the type three secretion system (T3SS) of S. flexneri to mediate a preemptive pyroptotic response to pathogens independently from invasion. Moreover, both invasive and non-invasive S. flexneri were found within Nlrc4-/- ileal organoids, suggesting that murine intestinal epithelial cells (IECs) may be capable of bacterial uptake. Transcriptional analysis further revealed that infection of Nlrc4-/- organoids with invasive or non-invasive S. flexneri resulted in the downregulation of inflammatory signaling. In addition, infection was associated with an enrichment for markers of the enteroendocrine cell (EEC) lineage, effects that required exposure to bacteria and were not recapitulated by bacteria-free supernatants. Together, our results reveal unexpected characteristics of host-bacterial interaction in primary murine IECs, which may shape the response to the microbiota and enteric pathogens at the intestinal mucosal surface.

Crohn's disease (CD) involves aberrant intestinal T cell immunity and genetic variants associated with disease development. Notably, mutations impairing NOD2 signaling represent the largest genetic risk factor for CD. Paradoxically, although NOD2 variants are associated with CD, its ligand, bacterial muramyl dipeptide, is a potent stimulator of immunity, long recognized as the minimal component required for the adjuvanticity of complete Freund's adjuvant. This paradox highlights a critical gap in our understanding of how NOD2 coordinates the innate-adaptive immune cross-talk required to maintain intestinal homeostasis. Here we show that NOD2 engagement by muramyl dipeptide drives T cell homing to the mesenteric lymph nodes during both homeostasis and infection. This recruitment promotes antigen-specific effector and memory T cell accumulation in the ileal lamina propria, a process essential for effective recall responses and clearance of secondary infection. Mechanistically, this process requires endothelial-intrinsic NOD2 expression, which drives a specialized transcriptional program for leukocyte recruitment.

The innate immune protein NLRC5 plays a key role in cancer immune surveillance. Reduced NLRC5 expression is associated with a poor prognosis for many types of cancers. Previously, we showed that mice with a myeloid-specific deletion of Nlrc5 (Nlrc5mø-KO) develop gastric lymphoid lesions to Helicobacter infection resembling early-stage marginal zone lymphoma. We hypothesized that NLRC5 deficiency may promote a tumor-permissive microenvironment mediated by tumor-associated macrophages (TAMs). Consistent with this hypothesis, splenic macrophages from Helicobacter-infected Nlrc5mø-KO mice had upregulated expression of genes encoding the TAM receptor tyrosine kinases, Axl and Mertk. The levels of AXL and MERTK gene expression and MERTK phosphorylation were increased in NLRC5-/- THP-1 macrophages when compared with WT cells. In response to Helicobacter stimulation, Nlrc5-/- macrophages had significantly elevated anti-inflammatory responses (IL-10, TGF-β, Socs1, Socs3) compared with WT cells. Importantly, Nlrc5-/-macrophages showed enhanced efferocytosis and reduced antigen presentation to CD8+ T cells. Pretreatment of macrophages with AXL and MERTK inhibitors (R428, UNC2025) resulted in reduced efferocytosis and phosphorylation of downstream signaling molecules, STAT3 and ERK1/2. We propose that defective NLRC5 signaling in macrophages leads to tumor-permissive responses, thereby promoting the development of gastric lymphoid neogenesis to Helicobacter infection.

IntroductionAstrocyte-specific cell surface antigen-2 (ACSA2) has been established as the gold-standard marker for isolating astrocytes via magnetic-activated cell sorting (MACS) or fluorescence-activated cell sorting (FACS) for downstream transcriptomic studies. In a prior study of the astrocyte response to cortical stroke, we used ACSA2-based cell sorting prior to single cell RNA sequencing (scRNAseq). We found a substantial population of ACSA2+ cells exhibiting robust microglial gene expression signatures, suggesting contamination of purified astrocyte preparations.MethodsAn intravenous antibody labeling strategy coupled with flow cytometry was used to determine whether contamination originated from circulating immune cells or microglia.ResultsContaminating cells were identified as CNS-resident microglia that express CD45, CD11b, and ACSA2.DiscussionThese findings caution against the usage of ACSA2 for astrocyte purification without exclusion markers to achieve high-purity astrocyte populations for downstream multi-omics analyses.

Inflammatory injury to the intestine triggers a reprogramming of the intestinal epithelium to a fetal-like state that drives rapid restoration of the epithelial barrier. Although the intestinal microbiota is a key modulator of inflammation, its role in influencing epithelial fetal-like stem cell reprogramming and consequent restitution remains unclear. Using irradiation (IR) injury as a model for small intestinal epithelium injury and repair, we found that the intestinal microbiota accelerated epithelial restitution by amplifying a repair-associated inflammatory response that promoted the emergence of fetal-like intestinal epithelial cells (IECs), marked by Ly6a and Clu. NOD2, the strongest genetic link to the development of Crohn's disease, was found to be expressed in fetal-like IECs following injury. Employing an ileal organoid model, we demonstrated that NOD2 activation by its peptidoglycan ligand potentiated an inflammatory gene signature characterized by interferon signaling, concurrent with enterocyte recovery. NOD2 deficiency exacerbated epithelial apoptosis following IR injury, whereas epithelial-specific NOD2 signaling promoted fetal-like IEC emergence and increased epithelial proliferation. Collectively, these findings reveal a pivotal role for the microbiota and NOD2-mediated microbial sensing in regulating fetal-like IEC fate after injury, thus contributing to the protective function of this microbial sensor during intestinal inflammation.

Intestinal protists are detected by the host innate immune system through mechanisms that remain poorly understood. Here, we demonstrate that Tritrichomonas protozoa induce thickening of the colonic mucus in an NLRP6-, ASC-, and caspase-11-dependent manner, consistent with the activation of sentinel goblet cells. Mucus growth is recapitulated with cecal extracts from Tritrichomonas-infected mice but not purified protozoa, suggesting that NLRP6 may detect infection-induced microbial dysbiosis. In agreement, Tritrichomonas infection causes a shift in the microbiota with the expansion of Bacteroides and Prevotella, and untargeted metabolomics reveals a dramatic increase in several classes of metabolites, including sphingolipids. Finally, using a combination of gnotobiotic mice and ex vivo mucus analysis, we demonstrate that wild-type, but not sphingolipid-deficient, B. thetaiotaomicron is sufficient to induce NLRP6-dependent sentinel goblet cell function, with the greatest effect observed in female mice. Thus, we propose that NLRP6 is a sensor of intestinal protozoa infection through monitoring microbial sphingolipids.

IL-18 is a member of the IL-1 family of cytokines, which is highly expressed in intestinal epithelial cells (IECs). Upon barrier breach, IL-18 is matured to its bioactive form as a result of inflammasome activation, released from the cell via Gasdermin D pores, and sensed by IL-18 receptor 1-positive (IL18R1+) immune cells to initiate an inflammatory response. In addition to this epithelial-out signaling network, we recently uncovered an epithelial-intrinsic IL-18 signaling pathway in the murine small intestine and identified enterochromaffin cells and revival stem cells (revSC) as IL18R1+ bearing IEC populations in the recovering crypt. Here, we discuss the mechanism, and physiological relevance, as well as some of the open questions presented by this discovery in relation to intestinal health and disease.

Abstract Background Crohn’s disease (CD) is a chronic disorder of unknown etiology. Genome-wide association studies have revealed that NOD2 loss of function mutations are an important gene contributor to CD pathogenesis. NOD2 is a pattern recognition receptor that responds to phosphorylated muramyl-dipeptide (MDP), whose production from peptidoglycan (PGN) is dependent on the expression of specific microbial hydrolases in the lumen. While a variety of studies have shown that reductions in NOD2 ligand and corresponding hydrolases, particularly DL-endopeptidases, occur in active CD or as a consequence of inflammation, which may play a role in sustaining disease, the interplay between NOD2 ligands and PGN-hydrolases pre-disease is unknown. Aims We investigated whether stool NOD2 ligand concentration is altered in pre-CD individuals, and the associations of PGN-hydrolase abundances with NOD2 ligand and with other pre-disease biomarkers. Methods Fecal samples were collected from healthy first-degree relatives of CD patients who were followed prospectively as part of the CCC-GEM project nested case control cohort (n = 91 pre-CD, n = 242 matched controls, median time to diagnosis 3.2 years). Fecal calprotectin (FCP), urinary fractional excretion ratio of lactulose to mannitol (LMR), and C-reactive protein (CRP) from serum were measured. PGN-hydrolase gene abundances was assessed by shotgun sequencing of stool samples. NOD2 ligand abundance was measured by incubating diluted stool supernatant with human NOD2 reporter HEK293 cells overnight then measuring OD640. A database of PGN-hydrolase clusters was generated by sequentially clustering with MMseqs2 based on sequence identity, then with Foldseek based on the AlphaFold Protein Structure Database. Results NOD2 ligand concentration was significantly reduced in pre-CD compared to matched controls (p < 0.01). Although several PGN-hydrolase clusters were negatively associated with NOD2 ligand, the relative abundance of one DL-endopeptidase cluster expressed by the Firmicutes phylum was significantly positively associated with NOD2 ligand abundance (q < 0.05). A DD-carboxypeptidase cluster, an amidase cluster, and a muramidase cluster were each negatively associated with future diagnosis of CD (q < 0.05). While many clusters were positively and negatively associated with FCP and CRP, one DD-carboxypeptidase cluster was positively associated with LMR (gut barrier permeability, q < 0.05). Conclusions These results show that NOD2 ligand concentration and the PGN-hydrolases that produce it are altered in pre-CD stool, suggesting that this may contribute to disease onset, however further investigation is needed. Funding Agencies CCC, CIHRHelmsley Charitable Trust, Mount Sinai Hospital

Apoptotic cells are immunosuppressive, creating a barrier in cancer treatment. Thus, we investigated immune responses to dying tumor cells after therapy in the tumor draining lymph node (TDLN). A key population responsible for clearing tumor material in the TDLN was medullary sinus macrophages (MSMs). Tumor debris phagocytosis by MSMs induces the cytokine IL-33, and blocking the IL-33 receptor (ST2) or deletion of Il33 in MSMs enhances therapy responses. Mechanistically, IL-33 activates T regulatory cells in TDLNs that migrate to the tumor to suppress CD8+ T cells. Therapeutically combining ST2 blockade, targeted kinase inhibitors, and anti-PD-1 immunotherapy increases CD8+ T cell activity promoting tumor regression. Importantly, we observe similar activity in human macrophages, and IL-33 expression in sentinel lymph nodes correlates with disease stage and survival in melanoma. Thus, our data identifies an IL-33-dependent immune response to therapy that attenuates therapy-induced anti-tumor immunity.

A preprint by Srivastava et al. reports that C19S modification of insulin, which occurs in response to a stressed microenvironment, promotes pro-inflammatory T cell activation and memory responses.

Upon injury, epithelial-derived IL-18 is released and induces an inflammatory response in underlying IL18R1+ lamina propria cells. Notably, Il18r1 is also predicted to be expressed and functional in intestinal epithelial cells (IECs), since epithelial IL18R1 deficiency contributes to worsened outcomes upon inflammatory challenge. However, the nature of Il18r1+ IECs, and their subsequent role in epithelial-intrinsic IL-18 signaling is poorly characterized. Here, we show that, in the murine small intestine, the IL-18 receptor is expressed by rare IECs that we identified to be a subset of enterochromaffin cells (ECC). While these cells are the major producers of serotonin in the intestine, we found no evidence that IL-18 regulated serotonin metabolism or release. Rather, upon radiation-induced injury, Il18r1+ cells appeared in the crypt base and took on a revival stem cell (revSC) program, marked by mixed expression of YAP/TAZ and enteroendocrine genes signatures. Functionally, irradiated Il18-/- mice display reduced epithelial proliferation and altered differentiation in the small intestine, characterized by increased Paneth cells (PC) and elevated Wnt3 levels, which was partially recapitulated in Il18-/- ileal organoids. In sum, we identified an Il18r1+ population in the epithelium and revealed a role for IEC-intrinsic IL-18 signaling during injury.

A microbiome's composition, stability, and response to perturbations are governed by its community interaction matrix, typically quantified through pairwise competition. However, in natural environments, microbes encounter multispecies interactions, complex conditions, and unculturable members. Moreover, evolutionary and ecological processes occur on overlapping timescales, making intra-species clonal diversity a critical but poorly understood factor influencing community interactions. Here, we present Dynamic Covariance Mapping (DCM), a general approach to infer microbiome interaction matrices from abundance time-series data. By combining DCM with high-resolution chromosomal barcoding, we quantify inter- and intra-species interactions during E. coli colonization in the mouse gut under three contexts: germ-free, antibiotic-perturbed, and innate microbiota. We identify distinct temporal phases in susceptible communities: (1) destabilization upon E. coli invasion, (2) partial recolonization of native bacteria, and (3) a quasi-steady state where E. coli sub-lineages coexist with resident microbes. These phases are shaped by specific interactions between E. coli clones and community members, emphasizing the dynamic and lineage-specific nature of microbial networks. Our results reveal how ecological and evolutionary dynamics jointly shape microbiome structure over time. The DCM framework provides a scalable method to dissect complex community interactions and is broadly applicable to bacterial ecosystems both in vitro and in situ.

ADP-heptose (ADP-Hep), a metabolite produced by gram-negative bacteria, is detected in the host cytosol by the kinase ALPK1, which engages TIFA-dependent innate immune responses. However, the function of ALPK1-TIFA signaling in primary cells and in physiological settings remains poorly understood. Here, we showed that, in the intestinal epithelium, ALPK1 and TIFA were mainly expressed by the intestinal stem cell (ISC) pool, where they controlled the replacement of homeostatic ISCs by new revival stem cells (revSCs) following injury. Mechanistically, ADP-Hep triggered pro-inflammatory nuclear factor κB (NF-κB) signaling and tumor necrosis factor (TNF)-dependent ISC apoptosis, which initiated a transforming growth factor β (TGF-β)- and YAP-dependent revSC program. Single-cell transcriptomics and lineage-tracing experiments identified Paneth cells as a cell of origin for revSC induction in response to ADP-Hep. In vivo, revSC emergence following irradiation or dextran-sodium-sulfate-induced injury was blunted in Tifa-/- mice. Together, our work reveals that ALPK1-TIFA signaling contributes to ISC turnover in response to bacterial detection in the intestine.

Abstract Aberrant resident memory T cell (TRM) responses have been associated with increased intestinal inflammation and Crohn’s disease (CD) pathology in humans. Genetic mutations in NOD2 are associated with the highest risk of CD development. NOD2 has been shown to be critical for initiating adaptive immune responses at systemic sites. However, the role of NOD2 in establishing memory T cell responses in the intestine remains unclear. Using an acute model of LCMV infection, we interrogated the role of NOD2 in intestinal memory T cell generation and function. Littermate wildtype or NOD2-deficient mice were infected intraperitoneally with LCMV-Armstrong, and the intestinal T cell priming, effector, and memory T cell responses were profiled in the mesenteric lymph nodes (mLN) and small intestinal lamina propria (SILP). Augmented NOD2 signalling at homeostasis and during infection increased endogenous and LCMV-specific CD4+ T cell numbers in the mLN, but not in the spleen. This effect was due to a NOD2-dependent increase in T cell homing to the mLN. Furthermore, NOD2-deficiency resulted in decreased effector and memory T cell numbers in the SILP. This effect was associated with decreased memory T cell functions in NOD2-deficient mice during ex vivo and in vivo recall experiments. Taken together, our experiments suggest a role for NOD2 in mediating optimal T cell priming in the mesenteric lymph nodes, which later affects effector and memory T cell functions in the intestine.

Abstract Background Inflammatory bowel disease is characterized by chronic inflammation of the gastrointestinal tract, resulting in recurrent injury to the intestinal epithelium. Restitution of the small intestinal epithelium is a coordinated response that involves the dedifferentiation of epithelial cell lineages, proliferation of Lgr5+ intestinal stem cells, and fetal-like stem cell reversion. While gut microbiota are critical mediators of intestinal inflammation, their impact on epithelial restitution remains unclear. Aims We aim to identify the how microbes regulate small intestinal epithelial restitution following damage. Our hypothesis is that gut microbiota accelerate restitution through pattern recognition receptor-driven signals following fetal-like stem cell reversion. Methods Irradiation (IR, 12Gγ) was used to induce a synchronized small intestinal epithelial restitution response in mice. Intestinal restitution kinetics were assessed transcriptionally (scRNA-Seq, qPCR) and histologically. Small intestinal organoids were used to assess epithelial restitution kinetics in vitro. Results ScRNA-Seq of small intestinal epithelial cells following IR from germ-free mice (GF), and specific pathogen-free mice (SPF) mice revealed that microbiota induced greater expression of fetal-like stem cell reversion markers, Ly6a and Clu, and greater expression of the proliferation marker, Pcna. These results were supported histologically as irradiated SPF mice observed an increase in fetal-like stem cells marked by Ly6a and Clu and an increase BrdU+ proliferating cells. ScRNA-seq and in situ hybridization highlighted that fetal-like intestinal stem cells upregulate expression of Nod2, a bacterial pattern recognition receptor. Using intestinal organoids to assess the function of Nod2, we observed that muramyl dipeptide driven Nod2-signlaing potentiates an interferon gene signature following IFNγ and TNFα co-stimulation. Further supporting the role for Nod2 in intestinal restitution, intestinal epithelium specific Nod2KO mice decreased BrdU+ proliferating cells post-IR compared to littermate controls. Conclusions Microbiota promote small intestinal restitution following IR through Nod2-signaling in fetal-like intestinal stem cells. Funding Agencies CIHR

Abstract Background Bacterial membrane vesicles (MVs) are bilipid nanoparticles secreted as a conserved method of intercellular communication. MVs from Gram-positive bacteria carry diverse bacterial products and represent a unique opportunity in the growing field of postbiotics. This native machinery for mediating microbe-host interactions makes MVs a promising tool for intestinal drug delivery in the context of Crohn’s disease (CD). CD is a chronic inflammatory bowel disease characterized by relapsing inflammation of the digestive tract. CD is associated with (1) loss of function mutations in the host gene encoding the nuclear-binding oligomerization domain 2 (NOD2) pattern recognition receptor and (2) a gut microbiome with reduced capabilities to generate NOD2 stimulating muropeptides from peptidoglycan. Nod2-/- mice have decreased barrier integrity and impaired epithelial restitution upon challenge. However, there are currently no therapeutic strategies targeting NOD2 for CD management. Aims The aims of this study were to (1) leverage MVs as a biological system for NOD2 ligand delivery to intestinal epithelial cells and (2) determine the roll of probiotic MVs and bacterial ligand synergy in wound re-epithelialization. Methods MVs were purified from B. subtilis through filtration and ultracentrifugation. MVs were characterized through nanoparticle tracking analysis using NanoSight300. WT and NOD2-/- HCT116 cells, a human colorectal carcinoma cell line, were utilized for IL-8 secretion quantification by ELISA, gene expression by qPCR, and in vitro scratch wound assay by Incucyte quantification. Results Here, we demonstrate for the first time that MVs from B. subtilis deliver NOD2 ligands in vitro. Treatment with isolated MVs induces IL8 secretion and CXCL1 expression in a NOD2-dependent manner. Furthermore, MVs promote re-epithelialization after in vitro scratch wounding. This effect was completely blunted by the addition of an inhibitor for RIPK2, a downstream transducer required for NOD2 signaling. Through bacterial pathogen-associated molecular patterns (PAMPs) screening, we found that wound re-epithelialization is promoted by PAMP synergy but dependent on RIPK2 signaling. Conclusions This work suggests that delivery of muropeptides by probiotic-derived MVs is a promising strategy to promote epithelial regeneration during injury through targeting NOD2. Future directions will work towards validating these findings in human ileal primary cells and murine models of intestinal injury. Funding Agencies CIHRMedicine by Design

Abstract Background Intestinal fibrosis (IF) is a common debilitating complication associated with Crohn’s disease (CD), an idiopathic inflammatory bowel disease (IBD). IF results in severe strictures that affect the entire gastrointestinal tract, often requiring surgery due to limited or no effective treatment. In general, IF is a consequence of chronic inflammation, excessive extracellular matrix (ECM) deposition, aberrant cellular functions and tissue remodeling involving the innate and adaptive immune system. At the cellular level, fibrosis has been proposed to involve the crosstalk between epithelial cells, mesenchymal stromal cells and immune cells. However, the cascade of events that establish IF is poorly understood as it comprises a dynamic interplay between host genetics, immunity, gut microbiome and aberrant environment insults. Notably, polymorphisms in nucleotide-binding oligomerization domain-containing protein 2 (NOD2; a bonafide cytosolic innate immune receptor), strong genetic risk factors for CD, also increase the incidence of IF. In this context, how NOD2 polymorphisms govern intestinal fibrostenosis in CD remains to be investigated. Aims To investigate how CD-associated risk gene, NOD2 contributes to intestinal fibrostenotic disease Methods We employed a single-cell RNA sequencing (scRNA-seq) approach to explore the cellular landscape in our CD-mouse model, where we challenged Nod2-deficient mice with a chronic inflammatory insult regime, using dextran sulfate sodium (cDSS) for 3 cycles. Subsequently, changes in inflammatory, metabolic and fibrotic markers in the gut were analyzed by quantitative real-time PCR (qRT-PCR), immunohistochemistry (IHC) or western blot analyses. Further, RNA-In-situ hybridization (RNA-ISH) and flow cytometric analyses were performed to validate cell populations contributing to, and the molecular signatures linked with intestinal fibrostenosis. Results We found that Nod2-deficient mice show increased expression of pro-inflammatory cytokines (TNF, IL6) and excessive ECM deposition (fibrosis) in the gut compared to wild-type littermate mice post-cDSS. Curiously, scRNA-seq analysis uncovered altered stromal-immune-cell crosstalk along with the identification of a novel subset of the Dpt+ interstitial stromal population with distinct gene signatures regulated by chronic inflammation. Further, we observed increased senescence (Cdkn2a) mediated trans-differentiation of stroma into fibroblast contributing to IF in Nod2-deficient mice. Conclusions The study outlined will deepen our understanding of cellular and molecular mediators as well as inter and intra-cellular networks that drive IF. This will be transformative in devising therapeutic strategies to prevent IF in progressive CD patients. Funding Agencies CCC, CIHRThe American Association of Immunologist (AAI)

Abstract Background Early life is a critical time for gut microbiome and immune development, including the establishment of proper host-microbe interactions. While exposures to western world environmental factors are associated with inflammatory bowel disease (IBD) susceptibility, the link between environment in early life and later disease onset is unclear. One of the most important western world environmental factors is diet, which can distinctly alter the gut microbiome. We believe an early life western-type diet (WD) can affect disease progression in a murine IL-10 KO colitis model through dysregulated T-cell responses against the microbiome. Aims We aimed to characterize how an early life WD given to IL-10 KO mice would affect colitis development and the gut microbiome. Methods IL-10 KO mice were housed in specific pathogen free conditions and fed normal chow (NC) or WD ad libitum, either between days 10 to 35 (early WD, eWD) or days 35 to 60 (adolescent WD, aWD). Stool was collected from mice at days 35, 56, and 84 for lipocalin-2 (LCN-2) and 16S rDNA sequencing. Mice were sacrificed at day 84, assessing mesenteric lymph node weight, gene expression, colon damage by histopathology, and colon lamina propria leukocyte (LPL) phenotype and cytokine expression by flow cytometry. Results Compared to NC and aWD, the eWD fed IL-10 KO mice displayed increased fecal LCN-2 at days 56 and 84, indicating greater inflammation. At sacrifice, eWD fed mice had larger mesenteric lymph nodes and more significant colon damage by histopathological scoring. Colon LPL preparations showed that eWD fed IL-10 KO mice had higher proportions and absolute numbers of effector and regulatory T-cells. Additionally, higher proportions and absolute numbers of those T-cells were IFNγ+, IL-17A+, and IL-22+. qPCR of distal colon tissue revealed increased gene expression of innate and type 3 proinflammatory cytokines such as Il1b, Tnfα, and Il23, while showing no change in Il6 and Il4. Taxa positively associated with WD were able to establish a persistent niche in eWD fed mice but not in aWD fed mice. An increase in only one specific taxon was associated with eWD at all timepoints while also most strongly correlating with inflammatory markers. Conclusions This data suggests that eWD feeding during gut microbiome and immune development is uniquely capable of increasing long-term susceptibility to intestinal inflammation in IL-10 KO mice. This appears to be associated with persistent colonization of potentially more inflammatory taxa. This work provides insight into the potential role of early life environmental risk factors, i.e. WD, in the later development of IBD. Funding Agencies CAG, CIHRUniversity of Toronto, Taconic Biosciences

The intestinal mucosa must balance tolerance to commensal microbes and luminal antigens with rapid detection of enteric pathogens in order to maintain homeostasis. This balance is facilitated through the regulation of epithelial layer integrity by innate immune receptors. Certain NOD-like receptors (NLRs) expressed in intestinal epithelial cells, including NLRC4 and NLRP9B, form inflammasomes that protect against pathogens by activating caspase-1 to cause extrusion of infected cells. NLRP1B is a murine NLR encoded by five alleles of a highly polymorphic gene homologous to human NLRP1. NLRP1B forms inflammasomes in response to a variety of pathogens that cause intestinal infections, but it has almost exclusively been studied in immune cells and has not been characterized in cells of the intestinal epithelium. Here, we show that Nlrp1b is expressed in ileal and colonic organoids derived for C57BL/6J mice. Nlrp1b was upregulated by interleukin-13 in organoids and by the protozoan Tritrichomonas muris in vivo, suggesting that NLRP1B may be involved in defense against enteric parasites. Surprisingly, while Val-boro-Pro (VbP) activated NLRP1B in bone marrow-derived macrophages, it did not activate NLRP1B in organoids. We furthermore did not detect Nlrp1b in organoids derived from Balb/cJ mice, which express a different allele than the one expressed in C57BL/6J mice. Together, our results suggest that NLRP1B may have an allele-dependent function in murine IECs whose regulation is distinct from that of macrophages.