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Lay Summary T-cell and antibody responses to severe acute respiratory syndrome coronavirus 2 vaccination in inflammatory bowel disease patients are poorly correlated. T-cell responses are preserved by most biologic therapies, but augmented by anti-tumor necrosis factor (anti-TNF) treatment. While anti-TNF therapy blunts the antibody response, cellular immunity after vaccination is robust.

BackgroundVaccination against SARS-CoV-2 is a highly effective strategy to protect against infection, which is predominantly mediated by vaccine-induced antibodies. Postvaccination antibodies are robustly produced by those with inflammatory bowel disease (IBD) even on immune-modifying therapies but are blunted by anti-TNF therapy. In contrast, T-cell response which primarily determines long-term efficacy against disease progression,, is less well understood. We aimed to assess the post-vaccination T-cell response and its relationship to antibody responses in patients with inflammatory bowel disease (IBD) on immune-modifying therapies.MethodsWe evaluated IBD patients who completed SARS-CoV-2 vaccination using samples collected at four time points (dose 1, dose 2, 2 weeks after dose 2, 8 weeks after dose 2). T-cell clonal analysis was performed by T-cell Receptor (TCR) immunosequencing. The breadth (number of unique sequences to a given protein) and depth (relative abundance of all the unique sequences to a given protein) of the T-cell clonal response were quantified using reference datasets and were compared to antibody responses.ResultsOverall, 303 subjects were included (55% female; 5% with prior COVID) (Table). 53% received BNT262b (Pfizer), 42% mRNA-1273 (Moderna) and 5% Ad26CoV2 (J&J). The Spike-specific clonal response peaked 2 weeks after completion of the vaccine regimen (3- and 5-fold for breadth and depth, respectively); no changes were seen for non-Spike clones, suggesting vaccine specificity. Reduced T-cell clonal depth was associated with chronologic age, male sex, and immunomodulator treatment. It was preserved by non-anti-TNF biologic therapies, and augmented clonal depth was associated with anti-TNF treatment. TCR depth and breadth were associated with vaccine type; after adjusting for age and gender, Ad26CoV2 (J&J) exhibited weaker metrics than mRNA-1273 (Moderna) (p=0.01 for each) or BNT262b (Pfizer) (p=0.056 for depth). Antibody and T-cell responses were only modestly correlated. While those with robust humoral responses also had robust TCR clonal expansion, a substantial fraction of patients with high antibody levels had only a minimal T-cell clonal response.ConclusionAge, sex and select immunotherapies are associated with the T-cell clonal response to SARS-CoV-2 vaccines, and T-cell responses are low in many patients despite high antibody levels. These factors, as well as differences seen by vaccine type may help guide reimmunization vaccine strategy in immune-impaired populations. Further study of the effects of anti-TNF therapy on vaccine responses are warranted.

INTRODUCTION: Patients with immune-mediated inflammatory diseases such as inflammatory bowel disease (IBD) on immunosuppressive and biologic therapies were largely excluded from severe acute respiratory syndrome coronavirus-2 messenger RNA vaccine trials. METHODS: We evaluated adverse events (AE) after messenger RNA vaccination in 246 adults with IBD participating in a longitudinal vaccine registry. RESULTS: In general, AE frequency was similar to that reported in the general population. AEs were more common among younger patients and those with previous COVID-19. AEs were less common in individuals receiving advanced therapies with biologics or small-molecule inhibitors. DISCUSSION: Those with IBD and other immune-mediated inflammatory diseases can be reassured that the AE risk is likely not increased, and may be reduced, while on advanced therapies.

Introduction: In the SARS-CoV2 mRNA vaccine trials, post-vaccination gastrointestinal (GI) symptoms were reported in 10-20% of participants. These symptoms could be perceived as inflammatory bowel disease (IBD) flare which could lead to patient anxiety, and unnecessary tests or treatment. We aimed to assess GI symptoms after SARS-CoV2 mRNA vaccination in patients with IBD relative to non-IBD healthcare workers (HCW). Methods: We assessed GI symptoms in adults with IBD and HCW at baseline and after each dose of a SARS-CoV-2 mRNA vaccine. We analyzed patient-reported IBD-specific disease activity (PRO2) after each dose (stool frequency (SF) and rectal bleeding for ulcerative colitis (UC), SF and abdominal pain for Crohn's disease (CD)). We also compared the frequency, severity, and duration of postvaccination GI symptoms in IBD patients compared to HCW. Severity was defined by impact on daily activities (mild, did not interfere;moderate, some interference;severe, prevented routine activity;extreme, required hospitalization). Severe and extreme were combined and designated as severe+. Duration was classified as 7 days. Results: Post-vaccination GI symptoms were assessed after dose 1 (D1) (1391 IBD, 933 HCW) and dose 2 (D2) (1271 IBD, 884 HCW) (Table). About 60% of IBD and>99% of HCW received the BNT162b vaccine (Pfizer);the remainder received mRNA-1273 (Moderna). New GI symptoms after D1 were more frequent among IBD than HCW (6.0% vs 2.9%, p=0.001) but not after D2 (12.1% vs 12.7%, p=NS). Relative to HCW, IBD patients reported more diarrhea (3.8% vs. 1% (p

Patients with immune-mediated inflammatory diseases (IMID) such as inflammatory bowel disease (IBD) on immunosuppressive and biologic therapies were largely excluded from SARS-CoV-2 mRNA vaccine trials. We thus evaluated post-mRNA vaccination adverse events (AE) in 246 vaccinated adults with IBD participating in a longitudinal vaccine registry. In general, AE frequency was similar to that reported in the general population. As in the general population, AE were more common among younger patients, and those with prior COVID-19. We additionally found that AE were less common in individuals receiving biologic therapy. Those with IBD and other IMID on these commonly prescribed therapies can be reassured that the AE risk is likely not increased, and may be reduced, while on biologics.

ObjectiveWe sought to determine the extent of SARS-CoV-2 seroprevalence and the factors associated with seroprevalence across a diverse cohort of healthcare workers.DesignObservational cohort study of healthcare workers, including SARS-CoV-2 serology testing and participant questionnaires.SettingsA multisite healthcare delivery system located in Los Angeles County.ParticipantsA diverse and unselected population of adults (n=6062) employed in a multisite healthcare delivery system located in Los Angeles County, including individuals with direct patient contact and others with non-patient-oriented work functions.Main outcomesUsing Bayesian and multivariate analyses, we estimated seroprevalence and factors associated with seropositivity and antibody levels, including pre-existing demographic and clinical characteristics; potential COVID-19 illness-related exposures; and symptoms consistent with COVID-19 infection.ResultsWe observed a seroprevalence rate of 4.1%, with anosmia as the most prominently associated self-reported symptom (OR 11.04, pConclusion and relevanceThe demographic factors associated with SARS-CoV-2 seroprevalence among our healthcare workers underscore the importance of exposure sources beyond the workplace. The size and diversity of our study population, combined with robust survey and modelling techniques, provide a vibrant picture of the demographic factors, exposures and symptoms that can identify individuals with susceptibility as well as potential to mount an immune response to COVID-19.

ImportanceAntibody testing is important for understanding patterns of exposure and potential immunity to SARS-CoV-2. Prior data on seroprevalence have been subject to variations in selection of individuals and nature as well as timing of testing in relation to exposures.ObjectiveWe sought to determine the extent of SARS-CoV-2 seroprevalance and the factors associated with seroprevelance across a diverse cohort of healthcare workers.DesignObservational cohort study of healthcare workers, including SARS-CoV-2 serology testing and participant questionaires.ParticipantsA diverse and unselected population of adults (n=6,062) employed in a multi-site healthcare delivery system located in Los Angeles County, including individuals with direct patient contact and others with non-patient-oriented work functions.ExposureExposure and infection with the SARS-CoV-2 virus, as determined by seropositivity.Main OutcomesUsing Bayesian and multi-variate analyses, we estimated seroprevalence and factors associated with seropositivity and antibody titers, including pre-existing demographic and clinical characteristics; potential Covid-19 illness related exposures; and, symptoms consistent with Covid-19 infection.ResultsWe observed a seroprevalence rate of 4.1%, with anosmia as the most prominently associated self-reported symptom in addition to fever, dry cough, anorexia, and myalgias. After adjusting for potential confounders, pre-existing medical conditions were not associated with antibody positivity. However, seroprevalence was associated with younger age, Hispanic ethnicity, and African-American race, as well as presence of either a personal or household member having a prior diagnosis of Covid-19. Importantly, African American race and Hispanic ethnicity were associated with antibody positivity even after adjusting for personal Covid-19 diagnosis status, suggesting the contribution of unmeasured structural or societally factors. Notably, number of people, or children, in the home was not associated with antibody positivity.Conclusion and RelevanceThe demographic factors associated with SARS-CoV-2 seroprevalence among our healthcare workers underscore the importance of exposure sources beyond the workplace. The size and diversity of our study population, combined with robust survey and modeling techniques, provide a vibrant picture of the demographic factors, exposures, and symptoms that can identify individuals with susceptibility as well as potential to mount an immune response to Covid-19.Key PointsQuestionWhat is the SARS-CoV-2 IgG seroprevalence rate across a large and diverse healthcare worker population, and which clinical, envionrmental, and symptom-based measures are associated with seropositivity?FindingsWe observed a seroprevalence rate of 4.1%. Adjusting for potential confounders, seropositivity was associated with younger age, Hispanic ethnicity, African-American race, and the symptom of anosmia, while not significantly associated with any pre-existing medical conditions.MeaningFactors associated with SARS-CoV-2 seroprevalence among our healthcare workers underscore the importance of exposure sources beyond the workplace.

Of individuals with SARS-CoV-2 IgG antibody testing performed, those who contemporaneously experienced a cluster of Covid-19 relevant symptoms in the 1-2 months preceding the antibody assay were more likely to test positive whereas those who experienced the symptom clustering in the prior 3-6 months were more likely to test negative. These findings suggest that antibodies likely wane over a period of months, particularly in relation to the timing of symptoms.

Background And Aims The largest cause of mortality in patients with inflammatory bowel disease (IBD) remains thromboembolic disease (TED). Recent reports have demonstrated that both monogenic and polygenic factors contribute to TED and 10% of healthy subjects are genetically at high risk for TED. Our aim was to utilize whole-exome sequencing and genome-wide genotyping to determine the proportion of IBD patients genetically at risk for TED and investigate the effect of genetic risk of TED in IBD. Methods The TED polygenic risk score was calculated from genome-wide genotyping. Thrombophilia pathogenic variants were extracted from whole-exome sequencing. In total, 792 IBD patients had both whole-exome sequencing and genotyping data. We defined patients at genetically high risk for TED if they had a high TED polygenic risk score or carried at least 1 thrombophilia pathogenic variant. Results We identified 122 of 792 IBD patients (15.4%) as genetically high risk for TED. Among 715 of 792 subjects whose documented TED status were available, 63 of the 715 patients (8.8%) had TED events. Genetic TED risk was significantly associated with increased TED event (odds ratio, 2.5; P = .0036). In addition, we confirmed an additive effect of monogenic and polygenic risk on TED (P = .0048). Patients with high TED genetic risk more frequently had thrombosis at multiple sites (78% vs 42%, odds ratio, 3.96; P = .048). Conclusions Genetic risk (both poly- and monogenic) was significantly associated with TED history. Our results suggest that genetic traits identify approximately 1 in 7 patients with IBD who will experience 2.5-fold or greater risk for TED.

We describe the rationale, design, and implementation of baseline enrollment for a longitudinal, observational cohort study of healthcare workers. The importance of workplace as a characteristic of interest in population-based studies has become increasingly apparent over time. Most adults spend a majority of their waking hours living in their workplace environment, which serves as a source of unique as well as shared exposures, stressors, and related determinants of health. A rapidly expanding segment of the working population includes those individuals who work in the fields of healthcare. The healthcare workforce, at large, represents an increasingly diverse subset of the population with broad exposures; some exposures are specific to the workplace and others are common to persons living in the community. Importantly, healthcare workers tend to have general interest and willingness to participate in research, in addition to stable employment and easy access to on-site clinical research assessment locations. Accordingly, from a population of individuals working at a large medical delivery network, we enrolled over 6300 healthcare workers into a cohort study involving survey data collection on medical history, work environment, and family and living situation; this information was linked to participant electronic health record data and collected biospecimens.

The host receptor for severe acute respiratory syndrome coronavirus 2, angiotensin-converting enzyme 2 (ACE2), is highly expressed in small bowel (SB). Our aim was to identify factors influencing intestinal ACE2 expression in Crohn's disease (CD), ulcerative colitis (UC), and non-inflammatory bowel disease (IBD) controls.Using bulk RNA sequencing or microarray transcriptomics from tissue samples (4 SB and 2 colonic cohorts; n = 495; n = 387 UC; n = 94 non-IBD), we analyzed the relationship between ACE2 with demographics and disease activity and prognosis. We examined the outcome of anti-tumor necrosis factor and anti-interleukin-12/interleukin-23 treatment on SB and colonic ACE2 expression in 3 clinical trials. Univariate and multivariate regression models were fitted.ACE2 levels were consistently reduced in SB CD and elevated in colonic UC compared with non-IBD controls. Elevated SB ACE2 was also associated with demographic features (age and elevated body mass index) associated with poor coronavirus disease 2019 outcomes. Within CD, SB ACE2 was reduced in patients subsequently developing complicated disease. Within UC, colonic ACE2 was elevated in active disease and in patients subsequently requiring anti-tumor necrosis factor rescue therapy. SB and colonic ACE2 expression in active CD and UC were restored by anti-cytokine therapy, most notably in responders.Reduced SB but elevated colonic ACE2 levels in IBD are associated with inflammation and severe disease, but normalized after anti-cytokine therapy, suggesting compartmentalization of ACE2-related biology in SB and colonic inflammation. The restoration of ACE2 expression with anti-cytokine therapy might be important in the context of severe acute respiratory syndrome coronavirus 2 infection and potentially explain reports of reduced morbidity from coronavirus disease 2019 in IBD patients treated with anti-cytokines.

IntroductionCoronavirus Disease 2019 (COVID-19) infection has been characterized by rapid spread and unusually large case clusters. It is important to have an estimate of the current state of COVID-19 epidemic in the U.S. to help develop informed public health strategies.MethodsWe estimated the potential scale of the COVID-19 epidemic (as of 03/01/2020) in the U.S. from cases ‘imported’ directly from Wuhan area. We used simulations based on transmission dynamics parameters estimated from previous studies and air traffic data from Wuhan to the U.S and deliberately built our model based on conservative assumptions. Detection and quarantine of individual COVID-19 cases in the U.S before 03/01/2020 were also taken into account. A SEIR model was used to simulate the growth of the number of infected individuals in Wuhan area and in the U.S.ResultsWith the most likely model, we estimated that there would be 9,484 infected cases (90%CI 2,054-24,241) as of 03/01/2020 if no successful intervention procedure had been taken to reduce the transmissibility in unidentified cases. Assuming current preventive procedures have reduced 25% of the transmissibility in unidentified cases, the number of infected cases would be 1,043 (90%CI 107-2,474).ConclusionOur research indicates that, as of 03/01/2020., it is likely that there are already thousands of individuals in the US infected with SARS-CoV-2. Our model is dynamic and is available to the research community to further evaluate as the situation becomes clearer.

Background CD is defined by transmural inflammation leading to inflammatory, stricturing and/or penetrating phenotypes. Identifying underlying molecular pathways and distinct disease subsets is critical for improved prognostics, therapeutics and biomarker discovery. Methods CD3+ T cells were purified from paired blood and mucosal tissue from 101 CD and 17 non-IBD subjects requiring surgery. Longitudinal samples (n = 30) were collected 4–13 mo. post-surgery. Expression profiles were generated by RNAseq, T-cell subset deconvolution by xCell and transcriptome-wide associations (TWAS) using TWAS-hub. Results Unsupervised clustering of peripheral T-cell gene expression at surgery revealed 2 CD profiles: Expression from cluster1, labelled CD-PBT (63%), clustered tightly with the non-IBD group. In cluster2, expression shifted from a peripheral toward a mucosal profile, labelled CD-PBmu(cosal) (37%). CD-PBmu was defined by differentially expressed genes (DEG) (1944 DEG, p < 0.001) regulating cell migration and adhesion pathways and a distinct T-cell subset composition associated with stricturing disease (p = 0.03), increased resected bowel length (p = 0.036) and post-op recurrence (p = 0.01). There were no significant differences in disease location/behaviour. Independent validation (5 public datasets) confirmed the CD-PBmu signature in data from whole blood (CD patients failing anti-TNF therapy, n = 204) and the mucosal-like expression profile in data from ileal tissue (paediatric CD patients, studies n = 751). A defining feature of CD-PBmu, validated in a separate CD cohort (n = 19), was decreased pro-inflammatory cytokine/chemokine and adhesion molecule expression following surgery (900 DEG, p < 0.001). No post-surgery change in expression was detected in CD-PBT. A 44-gene classifier was identified to enable clinical application. The classifier accurately detected the CD-PBmu patient subtype, correlated with the altered composition of peripheral T-cell subsets and overlapped with IBD associated TWAS signals (>60%). Recently, another group posed a blood-based 17 gene panel as predictive for aggressive IBD. These genes were not predictive for either the CD-PBmu or CD-PBT subtype ( Conclusion Severe CD can be stratified into 2 subtypes based on peripheral T-cell gene expression. Circulating T cells from CD-PBmu exhibit a mucosal-like gene signature, altered T-cell subset composition, clinical features of severity and decreased pro-inflammatory gene expression post-surgery. These findings hold potential to identify targets for CD subtype-specific therapeutic development. The 44-gene classifier overlapped with multiple paediatric CD datasets, suggesting the potential application of these findings for treatment stratification early in the disease process.

Background And Aims The host receptor for severe acute respiratory syndrome coronavirus 2, angiotensin-converting enzyme 2 (ACE2), is highly expressed in small bowel (SB). Our aim was to identify factors influencing intestinal ACE2 expression in Crohn's disease (CD), ulcerative colitis (UC), and non–inflammatory bowel disease (IBD) controls. Methods Using bulk RNA sequencing or microarray transcriptomics from tissue samples (4 SB and 2 colonic cohorts; n = 495; n = 387 UC; n = 94 non-IBD), we analyzed the relationship between ACE2 with demographics and disease activity and prognosis. We examined the outcome of anti–tumor necrosis factor and anti–interleukin-12/interleukin-23 treatment on SB and colonic ACE2 expression in 3 clinical trials. Univariate and multivariate regression models were fitted. Results ACE2 levels were consistently reduced in SB CD and elevated in colonic UC compared with non-IBD controls. Elevated SB ACE2 was also associated with demographic features (age and elevated body mass index) associated with poor coronavirus disease 2019 outcomes. Within CD, SB ACE2 was reduced in patients subsequently developing complicated disease. Within UC, colonic ACE2 was elevated in active disease and in patients subsequently requiring anti–tumor necrosis factor rescue therapy. SB and colonic ACE2 expression in active CD and UC were restored by anti-cytokine therapy, most notably in responders. Conclusions Reduced SB but elevated colonic ACE2 levels in IBD are associated with inflammation and severe disease, but normalized after anti-cytokine therapy, suggesting compartmentalization of ACE2-related biology in SB and colonic inflammation. The restoration of ACE2 expression with anti-cytokine therapy might be important in the context of severe acute respiratory syndrome coronavirus 2 infection and potentially explain reports of reduced morbidity from coronavirus disease 2019 in IBD patients treated with anti-cytokines.

Author(s): Whitfield, John B; Rahman, Khairunnessa; Haber, Paul S; Day, Christopher P; Masson, Steven; Daly, Ann K; Cordell, Heather J; Mueller, Sebastian; Seitz, Helmut K; Liangpunsakul, Suthat; Westerhold, Chi; Liang, Tiebing; Lumeng, Lawrence; Foroud, Tatiana; Nalpas, Bertrand; Mathurin, Philippe; Stickel, Felix; Soyka, Michael; Botwin, Gregory J; Morgan, Timothy R; Seth, Devanshi; GenomALC Consortium | Abstract: BackgroundThe risk of alcohol-related liver cirrhosis increases with increasing alcohol consumption, but many people with very high intake escape from liver disease. We postulate that susceptibility to alcoholic cirrhosis has a complex genetic component and propose that this can be dissected through a large and sufficiently powered genomewide association study (GWAS).MethodsThe GenomALC Consortium comprises researchers from Australia, France, Germany, Switzerland, United Kingdom, and United States, with a joint aim of exploring the genetic and genomic basis of alcoholic cirrhosis. For this National Institutes of Health/National Institute on Alcohol Abuse and Alcoholism funded study, we are recruiting high-risk drinkers who are either cases (with alcoholic cirrhosis) or controls (drinking comparable amounts over similar time, but free of significant liver disease). Extensive phenotypic data are obtained using semistructured interviews and patient records, and blood samples are collected.ResultsWe have successfully recruited 859 participants including 538 matched case-control samples as of September 2014, using study-specific inclusion-exclusion criteria and data collection protocols. Of these, 580 are cases (442 men and 138 women) and 279 are controls (205 men and 74 women). Duration of excessive drinking was slightly greater in cases than controls and was significantly less in women than men. Cases had significantly lower lifetime alcohol intake than controls. Both cases and controls had a high prevalence of reported parental alcohol problems, but cases were significantly more likely to report that a father with alcohol problems had died from liver disease (odds ratio 2.53, 95% confidence interval 1.31 to 4.87, pn=n0.0055).ConclusionsRecruitment of participants for a GWAS of alcoholic cirrhosis has proved feasible across countries with multiple sites. Affected patients often consume less alcohol than unaffected ones, emphasizing the existence of individual vulnerability factors. Cases are more likely to report liver disease in a father with alcohol problems than controls, consistent with a potential genetic component to the risk of alcoholic cirrhosis.

Bacterial infections occur in 25-35 % of cirrhotics admitted to hospital. Health-care associated and hospital acquired (nosocomial) infections are the most common epidemiology, with community acquired infections less common (15-30 %). Spontaneous bacterial peritonitis and urinary infections are the most common sites, with spontaneous bacteremia, pneumonia, cellulitis and other sites being less common. The risk of infection is increased among subjects with more severe liver disease and an infection in the past 6 months. Bacteria are isolated from approximately half of patients with a clinical diagnosis of infection. Gram-negative enterobacteriaceae are the most common organisms among community acquired infections; Gram-positive cocci are the most common organisms isolated among subjects with nosocomial infections. Up to 30 % of hospital associated infections are with multidrug resistant bacteria. Consequently, empiric antibiotic therapy that is recommended for community acquired infections is often inadequate for nosocomial infections. Infections worsen liver function. In-hospital and 1-year mortality of cirrhotics with infections is significantly higher than among cirrhotics without infection. In-hospital complications of infections, such as severe sepsis and septic shock, and mortality, are increased among subjects with multidrug-resistant infections as compared with cirrhotics with susceptible bacteria. Short-term antibiotic prophylaxis of cirrhotics with upper gastrointestinal bleeding and long-term antibiotic prophylaxis of selected cirrhotics with spontaneous bacterial peritonitis reduces infections and improves survival. Albumin administration to cirrhotics with SBP and evidence of advanced liver disease improves survival. The benefit of albumin administration to cirrhotics with infections other than SBP is under investigation.

Chronic hepatitis C virus (HCV) infection affects millions of individuals and is a significant cause of chronic liver disease and cirrhosis. Early treatment regimens relied on an immune-mediated response caused by interferon and only recently have medications acting directly on viral structures been discovered. In December 2013, two new medications, sofosbuvir and simeprevir, were approved by the US Food and Drug Administration (FDA) for treatment of chronic hepatitis C. This article reviews the approved treatment protocols for these two new medications and the clinical trials that fueled their development.

Clinical laboratory tests are now being prescribed and made directly available to consumers through retail outlets in the USA. Concerns with these test have been raised regarding the uncertainty of testing methods used in these venues and a lack of open, scientific validation of the technical accuracy and clinical equivalency of results obtained through these services.We conducted a cohort study of 60 healthy adults to compare the uncertainty and accuracy in 22 common clinical lab tests between one company offering blood tests obtained from finger prick (Theranos) and 2 major clinical testing services that require standard venipuncture draws (Quest and LabCorp). Samples were collected in Phoenix, Arizona, at an ambulatory clinic and at retail outlets with point-of-care services.Theranos flagged tests outside their normal range 1.6× more often than other testing services (P0.0001). Of the 22 lab measurements evaluated, 15 (68%) showed significant interservice variability (P0.002). We found nonequivalent lipid panel test results between Theranos and other clinical services. Variability in testing services, sample collection times, and subjects markedly influenced lab results.While laboratory practice standards exist to control this variability, the disparities between testing services we observed could potentially alter clinical interpretation and health care utilization. Greater transparency and evaluation of testing technologies would increase their utility in personalized health management.This work was supported by the Icahn Institute for Genomics and Multiscale Biology, a gift from the Harris Family Charitable Foundation (to J.T. Dudley), and grants from the NIH (R01 DK098242 and U54 CA189201, to J.T. Dudley, and R01 AG046170 and U01 AI111598, to E.E. Schadt).

Staphylococcus aureusis a major cause of community-acquired and nosocomial infections including the life-threatening conditions endocarditis, necrotizing pneumonia, necrotizing fasciitis, and septicemia. Toll-like receptor (TLR)-2, a membrane-bound microbial sensor, detects staphylococcal components, but macrophages lacking TLR2 or both TLR2 and TLR4 remainS. aureusresponsive, suggesting that an alternative microbial recognition receptor might be involved. The cytoplasmic sensor nucleotide-binding oligomerization domain containing (NOD) 2/caspase recruitment domain (CARD) 15 detects muramyl dipeptide from bacterial peptidoglycans and mediates cytokine responses toS. aureusin vitro, but the physiological significance of these observations is not well defined. Here we show that NOD2-deficient mice exhibit a delayed but ultimately exacerbated ulcerative response and impaired bacterial clearance after s.c. infection withS. aureus. NOD2-dependent recognition ofS. aureusand muramyl dipeptide is facilitated by α-toxin (α-hemolysin), a pore-forming toxin and virulence factor of the pathogen. The action of NOD2 is dependent on IL-1β-amplified production of IL-6, which promotes rapid bacterial killing by neutrophils. These results significantly broaden the physiological importance of NOD2 in innate immunity from the recognition of bacteria that primarily enter the cytoplasm to the detection of bacteria that typically reside extracellularly and demonstrate that this microbial sensor contributes to the discrimination between commensal bacteria and bacterial pathogens that elaborate pore-forming toxins.