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Abstract Background For unidentified reasons, possibly due to increased immune surveillance, patients with collagenous colitis (CC) and lymphocytic colitis (LC), both forms of microscopic colitis (MC), have lower risk of colorectal cancer than controls and ulcerative colitis (UC) patients. Levels of secreted and cell-bound mediators in MC patients with active disease and in histological remission (HR) compared to UC patients and controls were investigated. Methods Median fluorescence intensity of 54 analytes in colonic biopsies from patients with active CC (n = 21), LC (n = 11), and UC (n = 19); CC-HR (n = 6), LC-HR (n = 9), UC in remission (n = 19), non-diarrhea controls (n = 48), and diarrhea controls (n = 25) was measured using Luminex. Results Granzyme B and CCL5 levels were higher in active CC than in UC, whereas CCL4 and CD163 levels were similar in CC and UC, and both groups had higher levels of matrix metalloproteinase (MMP)-1, MMP-3, and tumor necrosis factor receptor II than both control groups. APRIL, BAFF, BCMA, CCL20, CXCL8, chitinase 3-like 1, pentraxin-3, Fas, and IL-33 were higher in UC than MC. Increases in 4-1BB and perforin in MC compared to controls were lower than in UC. Levels of gp130 and IL-6Rα were decreased in MC but increased in UC compared to controls. Conclusions Microscopic colitis patients exhibit increased levels of several analytes, including some associated with CD8+ T lymphocytes, suggesting a different pathogenesis of MC compared to UC. Higher levels of MMP-1 and MMP-3 in CC than LC indicate separate disease entities. Lay Summary Microscopic colitis patients have elevated colonic levels of numerous analytes compared to controls, with some being higher than in ulcerative colitis patients and associated with CD8+ cytotoxic T lymphocytes. These differences imply distinct pathogeneses of these diseases. Graphical Abstract Graphical Abstract

Microscopic colitis (MC) is a relatively common cause of chronic watery diarrhea, especially in older persons. Associated symptoms, including abdominal pain and arthralgias, are common. The diagnosis is based upon characteristic histological findings in the presence of diarrhea. The two types of MC, collagenous and lymphocytic colitis, share similar clinical features, with the main difference being the presence or absence of a thickened subepithelial collagen band. There are several treatment options for patients with MC, although only budesonide has been well studied in multiple controlled clinical trials. This review will describe the clinical features, epidemiology, pathophysiology, diagnostic criteria, and treatment of patients with MC.

Despite antiretroviral therapy (ART), some HIV-infected persons maintain lower than normal CD4(+) T-cell counts in peripheral blood and in the gut mucosa. This incomplete immune restoration is associated with higher levels of immune activation manifested by high systemic levels of biomarkers, including sCD14 and D-dimer, that are independent predictors of morbidity and mortality in HIV infection. In this 12-week, single-arm, open-label study, we tested the efficacy of IL-7 adjunctive therapy on T-cell reconstitution in peripheral blood and gut mucosa in 23 ART suppressed HIV-infected patients with incomplete CD4(+) T-cell recovery, using one cycle (consisting of three subcutaneous injections) of recombinant human IL-7 (r-hIL-7) at 20 µg/kg. IL-7 administration led to increases of both CD4(+) and CD8(+) T-cells in peripheral blood, and importantly an expansion of T-cells expressing the gut homing integrin α4β7. Participants who underwent rectosigmoid biopsies at study baseline and after treatment had T-cell increases in the gut mucosa measured by both flow cytometry and immunohistochemistry. IL-7 therapy also resulted in apparent improvement in gut barrier integrity as measured by decreased neutrophil infiltration in the rectosigmoid lamina propria 12 weeks after IL-7 administration. This was also accompanied by decreased TNF and increased FOXP3 expression in the lamina propria. Plasma levels of sCD14 and D-dimer, indicative of systemic inflammation, decreased after r-hIL-7. Increases of colonic mucosal T-cells correlated strongly with the decreased systemic levels of sCD14, the LPS coreceptor - a marker of monocyte activation. Furthermore, the proportion of inflammatory monocytes expressing CCR2 was decreased, as was the basal IL-1β production of peripheral blood monocytes. These data suggest that administration of r-hIL-7 improves the gut mucosal abnormalities of chronic HIV infection and attenuates the systemic inflammatory and coagulation abnormalities that have been linked to it.

Single-cell studies have revealed that intestinal macrophages maintain gut homeostasis through the balanced actions of reactive (inflammatory) and tolerant (noninflammatory) subpopulations. How such balance is impaired in inflammatory bowel diseases (IBDs), including Crohn’s disease (CD) and ulcerative colitis (UC), remains unresolved. Here, we define colon-specific macrophage states and reveal the critical role of noninflammatory colon-associated macrophages (niColAMs) in IBD recovery. Through trans-scale analyses—integrating computational transcriptomics, proteomics, and in vivo interventional studies—we identified GIV ( CCDC88A ) as a key regulator of niColAMs. GIV emerged as the top-ranked gene in niColAMs that physically and functionally interacts with NOD2, an innate immune sensor implicated in CD and UC. Myeloid-specific GIV depletion exacerbates infectious colitis, prolongs disease, and abolishes the protective effects of the NOD2 ligand muramyl dipeptide in colitis and sepsis models. Mechanistically, GIV’s C-terminus binds the terminal leucine-rich repeat 10 (LRR 10) of NOD2 and is required for NOD2 to dampen inflammation and clear microbes. The CD-associated 1007fs NOD2 variant, which lacks LRR 10, cannot bind GIV, which provides critical insights into how this clinically relevant variant impairs microbial sensing and clearance. These findings illuminate a critical GIV•NOD2 axis essential for gut homeostasis and highlight its disruption as a driver of dysbiosis and inflammation in IBD.

The T H 9 subset of helper T cells has specialized roles in parasite immunity. Neurath and colleagues show that T H 9 cells are also important for the pathogenesis of mouse and human colitis by disrupting gut barrier function. The molecular checkpoints that drive inflammatory bowel diseases are incompletely understood. Here we found more T cells expressing the transcription factor PU.1 and interleukin 9 (IL-9) in patients with ulcerative colitis. In an animal model, citrine reporter mice had more IL-9-expressing mucosal T cells in experimental oxazolone-induced colitis. IL-9 deficiency suppressed acute and chronic colitis. Mice with PU.1 deficiency in T cells were protected from colitis, whereas treatment with antibody to IL-9 suppressed colitis. Functionally, IL-9 impaired intestinal barrier function and prevented mucosal wound healing in vivo . Thus, our findings suggest that the T H 9 subset of helper T cells serves an important role in driving ulcerative colitis by regulating intestinal epithelial cells and that T H 9 cells represent a likely target for the treatment of chronic intestinal inflammation.

Background and aim: Interleukin (IL) 17 is a cytokine which exerts strong proinflammatory activities. In this study we evaluated changes in IL-17 expression in the inflamed mucosa and in the serum of patients with inflammatory bowel disease (IBD). Methods: Tissue samples were obtained endoscopically or surgically from patients with ulcerative colitis (UC) (n=20), Crohn’s disease (CD) (n=20), infectious colitis (n=5), ischaemic colitis (n=8), and normal colorectal tissues (n=15). IL-17 expression was evaluated by a standard immunohistochemical procedure. Serum IL-17 levels were determined by ELISA. IL-17 mRNA expression was analysed by reverse transcriptase-polymerase chain reaction. Results: IL-17 expression was not detected in samples from normal colonic mucosa, infectious colitis, or ischaemic colitis. In the inflamed mucosa of active UC and CD patients, IL-17 expression was clearly detectable in CD3+ T cells or CD68+ monocytes/macrophages. The average number of IL-17+ cells was significantly increased in active UC and CD patients compared with inactive patients. IL-17 mRNA expression was not detected in normal mucosa but was detectable in the mucosa from active UC and CD patients. IL-17 was not detected in the sera from normal individuals, infectious colitis, or ischaemic colitis patients but IL-17 levels were significantly elevated in IBD patients. Conclusions: IL-17 expression in the mucosa and serum was increased in IBD patients. It is likely that IL-17 expression in IBD may be associated with altered immune and inflammatory responses in the intestinal mucosa.

Background and AimsMany inflammatory bowel disease (IBD) patients do not respond to medical therapy. Tofacitinib is a first-in-class, partially selective inhibitor of Janus kinase, recently approved for treating patients with ulcerative colitis (UC). We describe our experience with the use of tofacitinib for treatment of patients with moderate-to-severe IBD.MethodsThis is a retrospective, observational study of the use of tofacitinib in IBD. Patients with medically resistant IBD were treated orally with 5 mg or 10 mg twice daily. Clinical response and adverse events were assessed at 8, 26, and 52 weeks. Objective response was assessed endoscopically, radiologically, and biochemically.Results58 patients (53 UC, 4 Crohn’s, 1 pouchitis) completed at least 8 weeks of treatment with tofacitinib. 93% of the patients previously failed treatment with anti-TNF. At 8 weeks of treatment, 21 patients (36%) achieved a clinical response, and 19 (33%) achieved clinical remission. Steroid-free remission at 8 weeks was achieved in 15 patients (26%). Of the 48 patients followed for 26 weeks, 21% had clinical, steroid-free remission. Of the 26 patients followed for 12 months, 27% were in clinical, steroid-free remission. Twelve episodes of systemic infections were noted, mostly while on concomitant steroids. One episode of herpes zoster infection was noted during follow-up.ConclusionsIn this cohort of patients with moderate-to-severe, anti-TNF resistant IBD, tofacitinib induced clinical response in 69% of the patients. 27% were in clinical, steroid-free remission by 1 year of treatment. Tofacitinib is an effective therapeutic option for this challenging patient population.

Abstract Background Vitamin D3 and vitamin D receptor (VDR) are involved in the pathogenesis of inflammatory bowel disease (IBD) and bacterial infection. Claudin-2 is a junction protein that mediates paracellular water transport in epithelia. Elevation of Claudin-2 is associated with active IBD. However, VDR involved in epithelial junctions under inflammation and infection remains largely unknown. We investigated the mechanisms on how VDR and Claudin-2 are related in inflamed states. Methods Using cultured VDR-/- enteroids, human intestinal epithelial cells, VDR-/- mice with Salmonella- or DSS-colitis, and human IBD samples, we investigated the mechanisms how VDR and Claudin-2 are related in inflamed states. Results After Salmonella infection had taken place, we observed significantly enhanced Claudin-2 and an increased bacterial invasion and translocation. A lack of VDR regulation led to a robust increase of Claudin-2 at the mRNA and protein levels post-infection. In DSS-treated VDR-/- mice, Claudin-2 was significantly increased. Location and quantification of Claudin-2 protein in the mouse colons treated with DSS also confirmed these results. Inflammatory cytokines were significantly higher in the serum and mRNA levels in intestine, which are known to increase Claudin-2. Furthermore, in inflamed intestine of ulcerative colitis patients, VDR expression was low and Claudin-2 was enhanced. Mechanistically, we identified the enhanced Claudin-2 promoter activity through the binding sites of NF-κB and STAT in inflamed VDR-/- cells. Conclusions Our studies have identified a new role for intestinal epithelial VDR in regulating barrier functions in the context of infection and inflammation.

A role for the IL-36 family of cytokines has been identified in the pathogenesis of psoriasis. Although significant mechanistic overlap can exist between psoriasis and inflammatory bowel disease (IBD), to date there have been no reports investigating the IL-36 family in gastrointestinal inflammation. Here we demonstrate that expression levels of IL-36α are specifically elevated in the colonic mucosa of ulcerative colitis patients. This elevated expression is mirrored in the inflamed colonic mucosa of mice, wherein IL-36 receptor deficiency confirmed this pathway as a mediator of mucosal inflammation. Il36r−/− mice exhibited reduced disease severity in an acute DSS-induced model of colitis in association with decreased innate inflammatory cell infiltration to the colon lamina propria. Consistent with these data, infection with the enteropathogenic bacteria Citrobacter rodentium, resulted in reduced innate inflammatory cell recruitment and increased bacterial colonization in the colons of il36r−/− mice. Il36r−/− mice also exhibited altered T helper cell responses in this model, with enhanced Th17 and reduced Th1 responses, demonstrating that IL-36R signaling also regulates intestinal mucosal T-cell responses. These data identify a novel role for IL-36 signaling in colonic inflammation and indicate that the IL-36R pathway may represent a novel target for therapeutic intervention in IBD.

Background The pathobiology of the non‐destructive inflammatory bowel disease (IBD) lymphocytic colitis (LC) is poorly understood. We aimed to define an LC‐specific mucosal transcriptome to gain insight into LC pathology, identify unique genomic signatures, and uncover potentially druggable disease pathways. Methods We performed bulk RNA‐sequencing of LC and collagenous colitis (CC) colonic mucosa from patients with active disease, and healthy controls (n = 4–10 per cohort). Differential gene expression was analyzed by gene‐set enrichment and deconvolution analyses to identify pathologically relevant pathways and cells, respectively, altered in LC. Key findings were validated using reverse transcription quantitative PCR and/or immunohistochemistry. Finally, we compared our data with a previous cohort of ulcerative colitis and Crohn's disease patients (n = 4 per group) to distinguish non‐destructive from classic IBD. Results LC can be subdivided into channelopathic LC, which is governed by organic acid and ion transport dysregulation, and inflammatory LC, which is driven by microbial immune responses. Inflammatory LC displays an innate and adaptive immunity that is limited compared to CC and classic IBD. Conversely, we noted a distinct induction of regulatory non‐coding RNA species in inflammatory LC samples. Moreover, compared with CC, water channel and cell adhesion molecule gene expression decreased in channelopathic LC, whereas it was accentuated in inflammatory LC and associated with reduced intestinal epithelial cell proliferation. Conclusions We conclude that LC can be subdivided into channelopathic LC and inflammatory LC that could be pathomechanistically distinct subtypes despite their shared clinical presentation. Inflammatory LC exhibits a dampened immune response compared to CC and classic IBDs. Our results point to regulatory micro‐RNAs as a potential disease‐specific feature that may be amenable to therapeutic intervention.