Oxylipins and metabolites from pyroptotic cells act as promoters of tissue repair.

Pyroptosis is a lytic cell death mode that helps limit the spread of infections and is also linked to pathology in sterile inflammatory diseases and autoimmune diseases1-4. During pyroptosis, inflammasome activation and the engagement of caspase-1 lead to cell death, along with the maturation and secretion of the inflammatory cytokine interleukin-1ß (IL-1ß). The dominant effect of IL-1ß in promoting tissue inflammation has clouded the potential influence of other factors released from pyroptotic cells. Here, using a system in which macrophages are induced to undergo pyroptosis without IL-1ß or IL-1α release (denoted Pyro-1), we identify unexpected beneficial effects of the Pyro-1 secretome. First, we noted that the Pyro-1 supernatants upregulated gene signatures linked to migration, cellular proliferation and wound healing. Consistent with this gene signature, Pyro-1 supernatants boosted migration of primary fibroblasts and macrophages, and promoted faster wound closure in vitro and improved tissue repair in vivo. In mechanistic studies, lipidomics and metabolomics of the Pyro-1 supernatants identified the presence of both oxylipins and metabolites, linking them to pro-wound-healing effects. Focusing specifically on the oxylipin prostaglandin E2 (PGE2), we find that its synthesis is induced de novo during pyroptosis, downstream of caspase-1 activation and cyclooxygenase-2 activity; further, PGE2 synthesis occurs late in pyroptosis, with its release dependent on gasdermin D pores opened during pyroptosis. As for the pyroptotic metabolites, they link to immune cell infiltration into the wounds, and polarization to CD301+ macrophages. Collectively, these data advance the concept that the pyroptotic secretome possesses oxylipins and metabolites with tissue repair properties that may be harnessed therapeutically.

Reverse translation approach generates a signature of penetrating fibrosis in Crohn's disease that is associated with anti-TNF response.

OBJECTIVE: Fibrosis is a common feature of Crohn's disease (CD) which can involve the mesenteric fat. However, the molecular signature of this process remains unclear. Our goal was to define the transcriptional signature of mesenteric fibrosis in CD subjects and to model mesenteric fibrosis in mice to improve our understanding of CD pathogenesis. DESIGN: We performed histological and transcriptional analysis of fibrosis in CD samples. We modelled a CD-like fibrosis phenotype by performing repeated colonic biopsies in mice and analysed the model by histology, type I collagen-targeted positron emission tomography (PET) and global gene expression. We generated a gene set list of essential features of mesenteric fibrosis and compared it to mucosal biopsy datasets from inflammatory bowel disease patients to identify a refined gene set that correlated with clinical outcomes. RESULTS: Mesenteric fibrosis in CD was interconnected to areas of fibrosis in all layers of the intestine, defined as penetrating fibrosis. We found a transcriptional signature of differentially expressed genes enriched in areas of the mesenteric fat of CD subjects with high levels of fibrosis. Mice subjected to repeated colonic biopsies showed penetrating fibrosis as shown by histology, PET imaging and transcriptional analysis. Finally, we composed a composite 24-gene set list that was linked to inflammatory fibroblasts and correlated with treatment response. CONCLUSION: We linked histopathological and molecular features of CD penetrating fibrosis to a mouse model of repeated biopsy injuries. This experimental system provides an innovative approach for functional investigations of underlying profibrotic mechanisms and therapeutic concepts in CD.

Can playing Spirograph lead to an ordered structure in self-propelled particles?

Understanding the local dynamics of microorganisms infecting a cell could help us develop efficient strategies to counter their aggregation. In the present study we have introduced a simple model of self-propelled particles (SPPs) with constant linear velocity, both in 2 and 3 dimensions, which captures the essential features of a microorganism's aggregation as well the dynamics around an attractive point (AP). The static behavior shows the presence of an icosahedral structure for a finite number of SPPs, and a hexagonal closed packed structure for an infinite number of SPPs, which was confirmed using Steinhardt bond order parameters for a 3-dimensional model. For a single SPP the dynamic behaviour involves the formation of orbits around the AP, which can be categorised into three dynamical regions based on the strength of coupling between the AP and SPP. For weak coupling we observe a rosette-like trajectory reminiscent of the pattern formed by the Spirograph toy. For intermediate coupling, circular trajectories were observed, and for very strong coupling the SPP was static and was always aligned with the AP. The radial distance from the AP to SPP was determined by the angular velocities of the SPP for the rosette-like region whereas for the circular and static regions, it was determined by the coupling constant. Even for a finite number of SPPs we observed the same behavior as long as the SPPs could rotate around the AP without colliding with each other.

Tandem tyrosine phosphosites in the Enteropathogenic Escherichia coli chaperone CesT are required for differential type III effector translocation and virulence.

Enteropathogenic Escherichia coli (EPEC) use a type 3 secretion system (T3SS) for injection of effectors into host cells and intestinal colonization. Here, we demonstrate that the multicargo chaperone CesT has two strictly conserved tyrosine phosphosites, Y152 and Y153 that regulate differential effector secretion in EPEC. Conservative substitution of both tyrosine residues to phenylalanine strongly attenuated EPEC type 3 effector injection into host cells, and limited Tir effector mediated intimate adherence during infection. EPEC expressing a CesT Y152F variant were deficient for NleA effector expression and exhibited significantly reduced translocation of NleA into host cells during infection. Other effectors were observed to be dependent on CesT Y152 for maximal translocation efficiency. Unexpectedly, EPEC expressing a CesT Y153F variant exhibited significantly enhanced effector translocation of many CesT-interacting effectors, further implicating phosphosites Y152 and Y153 in CesT functionality. A mouse infection model of intestinal disease using Citrobacter rodentium revealed that CesT tyrosine substitution variants displayed delayed colonization and were more rapidly cleared from the intestine. These data demonstrate genetically separable functions for tandem tyrosine phosphosites within CesT. Therefore, CesT via its C-terminal tyrosine phosphosites, has relevant roles beyond typical type III secretion chaperones that interact and stabilize effector proteins.

Properdin provides protection from Citrobacter rodentium-induced intestinal inflammation in a C5a/IL-6-dependent manner.

Citrobacter rodentium is an attaching and effacing mouse pathogen that models enteropathogenic and enterohemorrhagic Escherichia coli in humans. The complement system is an important innate defense mechanism; however, only scant information is available about the role of complement proteins during enteric infections. In this study, we examined the impact of the lack of properdin, a positive regulator of complement, in C. rodentium-induced colitis. Following infection, properdin knockout (P(KO)) mice had increased diarrhea and exacerbated inflammation combined with defective epithelial cell-derived IL-6 and greater numbers of colonizing bacteria. The defect in the mucosal response was reversed by administering exogenous properdin to P(KO) mice. Then, using in vitro and in vivo approaches, we show that the mechanism behind the exacerbated inflammation of P(KO) mice is due to a failure to increase local C5a levels. We show that C5a directly stimulates IL-6 production from colonic epithelial cells and that inhibiting C5a in infected wild-type mice resulted in defective epithelial IL-6 production and exacerbated inflammation. These outcomes position properdin early in the response to an infectious challenge in the colon, leading to complement activation and C5a, which in turn provides protection through IL-6 expression by the epithelium. Our results unveil a previously unappreciated mechanism of intestinal homeostasis involving complement, C5a, and IL-6 during bacteria-triggered epithelial injury.

Venous thromboembolism in reconstructive pelvic surgery.

OBJECTIVE: We sought to determine the incidence and risk factors for venous thromboembolism (VTE) in women undergoing reconstructive pelvic surgery (RPS). STUDY DESIGN: Using the American College of Surgeons National Surgical Quality Improvement Program registry, we identified patients who underwent RPS from 2006 through 2010 based on Current Procedural Terminology codes. We defined 2 cohorts: women with any RPS performed, with concomitant surgery from other specialties allowed (RPS + other), and women whose only procedure was RPS. VTE was defined as deep vein thrombosis or pulmonary embolism diagnosed within 30 days of surgery. Demographic characteristics, comorbidities, and operative characteristics were extracted from the database. Variables were analyzed using χ(2) tests and Student t tests for categorical and continuous variables. We performed a multiple logistic regression to control for confounding variables. RESULTS: In all, 20,687 women underwent RPS + other, with 69 cases of VTE for a rate of 0.3%. Multivariate analysis demonstrated predictors for postoperative VTE including inpatient hospital status (odds ratio [OR], 7.69; P < .001), higher American Society of Anesthesiology Physical Status classification (OR, 2.70; P < .001), and emergency intervention (OR, 3.65; P = .008). When women undergoing only RPS were analyzed, there were 14 cases of VTE, with an incidence of 0.1% and the only specific predictor for postoperative VTE was length of stay (P < .037). CONCLUSION: The incidence of VTE following RPS is very low, but it is increased in women undergoing concomitant surgeries. Patients undergoing inpatient surgery with higher American Society of Anesthesiology Physical Status classifications and requiring emergency intervention were at highest risk for VTE.

Western diet reduces small intestinal intraepithelial lymphocytes via FXR-Interferon pathway.

The prevalence of obesity in the United States has continued to increase over the past several decades. Understanding how diet-induced obesity modulates mucosal immunity is of clinical relevance. We previously showed that consumption of a high fat, high sugar "Western" diet (WD) reduces the density and function of small intestinal Paneth cells, a small intestinal epithelial cell type with innate immune function. We hypothesized that obesity could also result in repressed gut adaptive immunity. Using small intestinal intraepithelial lymphocytes (IEL) as a readout, we found that in non-inflammatory bowel disease (IBD) subjects, high body mass index correlated with reduced IEL density. We recapitulated this in wild type (WT) mice fed with WD. A 4-week WD consumption was able to reduce IEL but not splenic, blood, or bone marrow lymphocytes, and the effect was reversible after another 2 weeks of standard diet (SD) washout. Importantly, WD-associated IEL reduction was not dependent on the presence of gut microbiota, as WD-fed germ-free mice also showed IEL reduction. We further found that WD-mediated Farnesoid X Receptor (FXR) activation in the gut triggered IEL reduction, and this was partially mediated by intestinal phagocytes. Activated FXR signaling stimulated phagocytes to secrete type I IFN, and inhibition of either FXR or type I IFN signaling within the phagocytes prevented WD-mediated IEL loss. Therefore, WD consumption represses both innate and adaptive immunity in the gut. These findings have significant clinical implications in the understanding of how diet modulates mucosal immunity.

NAD+ precursors and bile acid sequestration treat preclinical refractory environmental enteric dysfunction.

Environmental enteric dysfunction (EED) is a diffuse small bowel disorder associated with poor growth, inadequate responses to oral vaccines, and nutrient malabsorption in millions of children worldwide. We identify loss of the small intestinal Paneth and goblet cells that are critical for innate immunity, reduced villous height, increased bile acids, and dysregulated nicotinamide adenine dinucleotide (NAD+) synthesis signaling as potential mechanisms underlying EED and which also correlated with diminished length-for-age z score. Isocaloric low-protein diet (LPD) consumption in mice recapitulated EED histopathology and transcriptomic changes in a microbiota-independent manner, as well as increases in serum and fecal bile acids. Children with refractory EED harbor single-nucleotide polymorphisms in key enzymes involved in NAD+ synthesis. In mice, deletion of Nampt, the gene encoding the rate-limiting enzyme in the NAD+ salvage pathway, from intestinal epithelium also reduced Paneth cell function, a deficiency that was further aggravated by LPD. Separate supplementation with NAD+ precursors or bile acid sequestrant partially restored LPD-associated Paneth cell defects and, when combined, fully restored all histopathology defects in LPD-fed mice. Therapeutic regimens that increase protein and NAD+ contents while reducing excessive bile acids may benefit children with refractory EED.

Impact of preoperative myocardial infarction on surgical outcomes in inpatient orthopaedic surgery.

PURPOSE: The purpose of this study was to evaluate the impact of a preoperative myocardial infarction (MI) on outcomes of inpatient orthopaedic operations. METHODS: The National Surgical Quality Improvement Program database was used to identify patients who underwent common orthopaedic operations from 2006 to 2010. Patient demographic data, comorbidities, complications, and lengths of stay were collected. Multivariate logistic regression and linear regression models were used to compare outcomes for patients with and without a history of MI in the six months prior to surgery. RESULTS: Of the 32,462 patients identified, 86 had sustained an MI in the six months prior to surgery. The MI cohort had no cardiac complications but had increased incidences of superficial surgical site infection, unplanned re-intubation, ventilator-assisted respiration for more than 48 hours, pneumonia, sepsis or septic shock, and postoperative mortality within 30 days of surgery, as well as prolonged lengths of stay. Following logistic regression to adjust for baseline differences, a history of MI showed no association with cardiac complications and was significantly associated with superficial surgical site infection (OR 3.6, 95% CI 1.1-11.8), ventilator dependence for over 48 hours (OR 4.0, 95% CI 1.1-14.0), and extended length of stay (median with interquartile range 4 [4-4] vs. 5 [5-5] days). CONCLUSIONS: A myocardial infarction within six months prior to orthopaedic surgery is not associated with a higher risk of 30-day perioperative cardiac complications; however, it is associated with increased rates of surgical site infection, prolonged ventilator dependence, and longer hospital stay.

Western diet induces Paneth cell defects through microbiome alterations and farnesoid X receptor and type I interferon activation.

Intestinal Paneth cells modulate innate immunity and infection. In Crohn's disease, genetic mutations together with environmental triggers can disable Paneth cell function. Here, we find that a western diet (WD) similarly leads to Paneth cell dysfunction through mechanisms dependent on the microbiome and farnesoid X receptor (FXR) and type I interferon (IFN) signaling. Analysis of multiple human cohorts suggests that obesity is associated with Paneth cell dysfunction. In mouse models, consumption of a WD for as little as 4 weeks led to Paneth cell dysfunction. WD consumption in conjunction with Clostridium spp. increased the secondary bile acid deoxycholic acid levels in the ileum, which in turn inhibited Paneth cell function. The process required excess signaling of both FXR and IFN within intestinal epithelial cells. Our findings provide a mechanistic link between poor diet and inhibition of gut innate immunity and uncover an effect of FXR activation in gut inflammation.

Debaryomyces is enriched in Crohn's disease intestinal tissue and impairs healing in mice.

Alterations of the mycobiota composition associated with Crohn's disease (CD) are challenging to link to defining elements of pathophysiology, such as poor injury repair. Using culture-dependent and -independent methods, we discovered that Debaryomyces hansenii preferentially localized to and was abundant within incompletely healed intestinal wounds of mice and inflamed mucosal tissues of CD human subjects. D. hansenii cultures from injured mice and inflamed CD tissues impaired colonic healing when introduced into injured conventionally raised or gnotobiotic mice. We reisolated D. hansenii from injured areas of these mice, fulfilling Koch's postulates. Mechanistically, D. hansenii impaired mucosal healing through the myeloid cell-specific type 1 interferon-CCL5 axis. Taken together, we have identified a fungus that inhabits inflamed CD tissue and can lead to dysregulated mucosal healing.

PAI-1 augments mucosal damage in colitis.

There is a major unmet clinical need to identify pathways in inflammatory bowel disease (IBD) to classify patient disease activity, stratify patients that will benefit from targeted therapies such as anti-tumor necrosis factor (TNF), and identify new therapeutic targets. In this study, we conducted global transcriptome analysis to identify IBD-related pathways using colon biopsies, which highlighted the coagulation gene pathway as one of the most enriched gene sets in patients with IBD. Using this gene-network analysis across 14 independent cohorts and 1800 intestinal biopsies, we found that, among the coagulation pathway genes, plasminogen activator inhibitor-1 (PAI-1) expression was highly enriched in active disease and in patients with IBD who did not respond to anti-TNF biologic therapy and that PAI-1 is a key link between the epithelium and inflammation. Functionally, PAI-1 and its direct target, the fibrinolytic protease tissue plasminogen activator (tPA), played an important role in regulating intestinal inflammation. Intestinal epithelial cells produced tPA, which was protective against chemical and mechanical-mediated colonic injury in mice. In contrast, PAI-1 exacerbated mucosal damage by blocking tPA-mediated cleavage and activation of anti-inflammatory TGF-ß, whereas the inhibition of PAI-1 reduced both mucosal damage and inflammation. This study identifies an immune-coagulation gene axis in IBD where elevated PAI-1 may contribute to more aggressive disease.

Temporal Regulation of the Bacterial Metabolite Deoxycholate during Colonic Repair Is Critical for Crypt Regeneration.

Colonic wound repair is an orchestrated process, beginning with barrier re-establishment and followed by wound channel formation and crypt regeneration. Elevated levels of prostaglandin E2 (PGE2) promote barrier re-establishment; however, we found that persistently elevated PGE2 hinders subsequent repair phases. The bacterial metabolite deoxycholate (DCA) promotes transition through repair phases via PGE2 regulation. During barrier re-establishment, DCA levels are locally diminished in the wound, allowing enhanced PGE2 production and barrier re-establishment. However, during transition to the wound channel formation phase, DCA levels increase to inhibit PGE2 production and promote crypt regeneration. Altering DCA levels via antibiotic treatment enhances PGE2 levels but impairs wound repair, which is rescued with DCA treatment. DCA acts via its receptor, farnesoid X receptor, to inhibit the enzyme cPLA2 required for PGE2 synthesis. Thus, colonic wound repair requires temporally regulated signals from microbial metabolites to coordinate host-associated signaling cascades. VIDEO ABSTRACT.

Predictors of adverse events after neck dissection: An analysis of the 2006-2011 National Surgical Quality Improvement Program (NSQIP) Database.

While neck dissection is an important primary and adjunctive procedure in the treatment of head and neck cancer, there is a paucity of studies evaluating outcomes. A retrospective review of the National Surgical Quality Improvement Program (NSQIP) database was performed to identify factors associated with adverse events (AEs) in patients undergoing neck dissection. A total of 619 patients were identified, using CPT codes specific to neck dissection. Of the 619 patients undergoing neck dissection, 142 (22.9%) experienced an AE within 30 days of the surgical procedure. Risk factors on multivariate regression analysis associated with increased AEs included dyspnea (odds ratio [OR] 2.57; 95% confidence interval [CI] 1.06 to 6.22; p = 0.037), previous cardiac surgery (OR 3.38; 95% CI 1.08 to 10.52; p = 0.036), increasing anesthesia time (OR 1.005; 95% CI 1 to 1.009; p = 0.036), and increasing total work relative value units (OR 1.09; CI 1.04 to 1.13; p < 0.001). The current study is the largest, most robust analysis to identify specific risk factors associated with AEs after neck dissection. This information will assist with preoperative optimization, patient counseling, and appropriate risk stratification, and it can serve as benchmarking for institutions comparing surgical outcomes.

Erdheim-Chester Disease presenting with histiocytic colitis and cytokine storm.

BACKGROUND: Non-Langerhans histiocytosis is a group of inflammatory lymphoproliferative disorders originating from non-clonal expansion of hematopoietic stem cells into cytokine-secreting dendritic cells or macrophages. Erdheim-Chester Disease (ECD) is a rare type of non-Langerhans cell histiocytosis characterized by tissue inflammation and injury caused by macrophage infiltration and histologic findings of foamy histiocytes. Often ECD involves the skeleton, retroperitoneum and the orbits. This is the first report documenting ECD manifesting as segmental colitis and causing cytokine-release syndrome. CASE PRESENTATION: A 68-year old woman presented with persistent fever without infectious etiology and hematochezia. Endoscopy showed segmental colitis and pathology revealed infiltration of large foamy histiocytes CD3-/CD20-/CD68+/CD163+/S100- consistent with ECD. The patient was empirically treated with steroids but continued to have fever and developed progressive distributive shock. CONCLUSION: This case report describes the differential diagnosis of infectious and immune-mediated inflammatory and rheumatologic segmental colitis. Non-Langerhans histiocytosis and ECD are rare causes of gastrointestinal inflammation. Prompt diagnosis is imperative for the appropriate treatment to prevent hemodynamic compromise due to distributive shock or gastrointestinal bleeding. Importantly, gastrointestinal ECD might exhibit poor response to steroid treatment and other potential treatments including chemotherapy, and biologic treatments targeting IL-1 and TNF-alpha signalling should be considered.

The microbial metabolite desaminotyrosine protects from influenza through type I interferon.

The microbiota is known to modulate the host response to influenza infection through as-yet-unclear mechanisms. We hypothesized that components of the microbiota exert effects through type I interferon (IFN), a hypothesis supported by analysis of influenza in a gain-of-function genetic mouse model. Here we show that a microbially associated metabolite, desaminotyrosine (DAT), protects from influenza through augmentation of type I IFN signaling and diminution of lung immunopathology. A specific human-associated gut microbe, Clostridium orbiscindens, produced DAT and rescued antibiotic-treated influenza-infected mice. DAT protected the host by priming the amplification loop of type I IFN signaling. These findings show that specific components of the enteric microbiota have distal effects on responses to lethal infections through modulation of type I IFN.

Do antimicrobial peptides and complement collaborate in the intestinal mucosa?

It is well understood that multiple antimicrobial peptides (AMPs) are constitutively deployed by the epithelium to bolster the innate defenses along the entire length of the intestines. In addition to this constitutive/homeostatic production, AMPs may be inducible and levels changed during disease. In contrast to this level of knowledge on AMP sources and roles in the intestines, our understanding of the complement cascade in the healthy and diseased intestines is rudimentary. Epithelial cells make many complement proteins and there is compelling evidence that complement becomes activated in the lumen. With the common goal of defending the host against microbes, the opportunities for cross-talk between these two processes is great, both in terms of actions on the target microbes but also on regulating the synthesis and secretion of the alternate family of molecules. This possibility is beginning to become apparent with the finding that colonic epithelial cells possess anaphylatoxin receptors. There still remains much to be learned about the possible points of collaboration between AMPs and complement, for example, whether there is reciprocal control over expression in the intestinal mucosa in homeostasis and restoring the balance following infection and inflammation.

ASA class is a reliable independent predictor of medical complications and mortality following surgery.

METHODS: The American Society of Anesthesiologists Physical Status classification system (ASA PS) is a method of characterizing patient operative risk on a scale of 1-5, where 1 is normal health and 5 is moribund. Every anesthesiologist is trained in this measure, and it is performed before every procedure in which a patient undergoes anesthesia. We measured the independent predictive value of ASA-PS for complications and mortality in the ACS-NSQIP database by multivariate regression. We conducted analogous regressions after standardizing ASA-PS to control for interprocedural variations in risk in the overall model and sub-analyses by surgical specialty and the most common procedures. RESULTS: For 2,297,629 cases (2005-2012; median age 55, min = 16, max > 90 [90 and above are coded as 90+]), at increasing levels of ASA-PS (2-5), odds ratios (OR's) from 2.05 to 63.25 (complications, p < 0.001) and 5.77-2011.92 (mortality, p < 0.001) were observed, with non-overlapping 95% confidence intervals. Standardization of ASA-PS (OR = 1.426 [per standard deviation above the mean ASA-PS per procedure], p < .001) and subgroup analyses yielded similar results. DISCUSSION: ASA PS was not only found to be associated with increased morbidity and mortality, but independently predictive when controlling for other comorbidities. Even after standardization based on procedure type, increases in ASA predicted significant increases in complication rates for morbidity and mortality post-operatively. CONCLUSIONS: ASA PS has strong, independent associations with post-operative medical complications and mortality across procedures. This capability, along with its simplicity, makes it a valuable prognostic metric.

Properdin Regulation of Complement Activation Affects Colitis in Interleukin 10 Gene-Deficient Mice.

BACKGROUND: Interleukin 10-deficient mice (IL-10(-/-)) are a popular model used to dissect the mechanisms underlying inflammatory bowel diseases. The role of complement, a host defense mechanism that bridges the innate and adaptive immune systems, has not been described in this model. We therefore studied the effect of deficiency of properdin, a positive regulator of complement, on colitis in mice with the IL-10(-/-) background. METHODS: For acute colitis, IL-10(-/-) and IL-10/properdin double knockout (DKO) or radiation bone marrow-reconstituted chimeric mice, had piroxicam added to their powdered chow for 14 days. For chronic colitis, 2.5% dextran sodium sulfate was added to the animals' water for 4 days then the mice were killed 8 weeks later. Colons were assessed for inflammation, cell infiltration, and cytokine and complement measurements. Bacterial translocation was measured by cultivating bacteria from organs on Luria broth agar plates. RESULTS: C3a and C5a levels and C9 deposition were all increased in piroxicam-fed IL-10(-/-) mice compared with mice not fed piroxicam. Piroxicam-fed DKO mice lacked increased C5a and C9 deposition combined with exacerbated colitis, reduced numbers of infiltrating neutrophils, and markedly higher local and systemic bacterial numbers compared with IL-10(-/-) mice. Bone marrow cells from IL-10(-/-) mice were sufficient to restore protection against the heightened colitis in piroxicam-fed DKO mice. CONCLUSIONS: Complement is activated in the IL-10(-/-) mouse mucosa in a properdin-dependent manner. In the absence of terminal complement activation, the inflammation is heightened, likely due to a lack of neutrophil control over microbes escaping from the intestines.