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Sphingosine-1-phosphate (S1P) is a bioactive lipid metabolite that exerts its actions by engaging 5 G-protein-coupled receptors (S1PR1-S1PR5). S1P receptors are involved in several cellular and physiological events, including lymphocyte/hematopoietic cell trafficking. An S1P gradient (low in tissues, high in blood), maintained by synthetic and degradative enzymes, regulates lymphocyte trafficking. Because lymphocytes live long (which is critical for adaptive immunity) and recirculate thousands of times, the S1P-S1PR pathway is involved in the pathogenesis of immune-mediated diseases. The S1PR1 modulators lead to receptor internalization, subsequent ubiquitination, and proteasome degradation, which renders lymphocytes incapable of following the S1P gradient and prevents their access to inflammation sites. These drugs might also block lymphocyte egress from lymph nodes by inhibiting transendothelial migration. Targeting S1PRs as a therapeutic strategy was first employed for multiple sclerosis (MS), and four S1P modulators (fingolimod, siponimod, ozanimod, and ponesimod) are currently approved for its treatment. New S1PR modulators are under clinical development for MS, and their uses are being evaluated to treat other immune-mediated diseases, including inflammatory bowel disease (IBD), rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and psoriasis. A clinical trial in patients with COVID-19 treated with ozanimod is ongoing. Ozanimod and etrasimod have shown promising results in IBD; while in phase 2 clinical trials, ponesimod has shown improvement in 77% of the patients with psoriasis. Cenerimod and amiselimod have been tested in SLE patients. Fingolimod, etrasimod, and IMMH001 have shown efficacy in RA preclinical studies. Concerns relating to S1PR modulators are leukopenia, anemia, transaminase elevation, macular edema, teratogenicity, pulmonary disorders, infections, and cardiovascular events. Furthermore, S1PR modulators exhibit different pharmacokinetics; a well-established first-dose event associated with S1PR modulators can be mitigated by gradual up-titration. In conclusion, S1P modulators represent a novel and promising therapeutic strategy for immune-mediated diseases.

Background & Aims: Integrin α4β7 mediates lymphocyte trafficking to the gut and gut-associated lymphoid tissues, a process critical for recruitment of effector lymphocytes from the circulation to the gut mucosa in inflammatory bowel disease (IBD) and murine models of intestinal inflammation. Antibody blockade of β7 integrins generally is efficacious in IBD; however, some patients fail to respond, and a few patients can experience exacerbations. This study examined the effects of loss of β7 integrin function in murine models of IBD. Methods: In a mouse IBD model caused by lack of interleukin 10, a cytokine important in CD25hiFoxP3+ regulatory T cell (Treg) function, genetic deletion of β7 integrin or antibody blockade of α4β7–mucosal addressin cell adhesion molecule-1 interaction paradoxically exacerbated colitis. Results: Loss of β7 impaired the capacity of Tregs homing to the gut and therefore suppress intestinal inflammation in an adoptive T-cell transfer model; however, the intrinsic suppressive function of β7-deficient Tregs remained intact, indicating that the β7 deficiency selectively impacts gut homing. Deletion of β7 integrin did not worsen colitis in an acute dextran sodium sulfate model in which Treg number and function were normal. Conclusions: In Integrin subunit beta (Itgb)7-/-Il10-/- mice, loss of β7-dependent Treg homing to gut-associated lymphoid tissues combined with loss of intrinsic Treg function exacerbated intestinal inflammation. These results suggest that IBD patients with reduced CD25hiFoxP3+ Treg numbers or function or lack of interleukin 10 could be at risk for failure of α4β7 blocking therapy. Keywords: Integrin β7 Blockade, Inflammatory Bowel Disease, Regulatory T Cells, Gut-Associated Lymphoid Tissue

Crohn’s disease (CD) is an inflammatory bowel disease, which can involve any region of the gastrointestinal tract. First described in 1932 as terminal ileitis or regional enteritis, it predominately involves the ileum with or without colonic involvement. Isolated colonic CD was first described in 1960 and since then the phenotypic classification of CD has evolved to stratify patients into isolated ileal, ileocolonic, or isolated colonic involvement. In the current review we evaluate the published literature regarding differences in epidemiology, natural history, pathogenesis, response to therapy, and disease monitoring, when stratified by disease location. Based on the available evidence consideration could be given to a new classification for CD, which splits it into ileum dominant (isolated ileal and ileocolonic) and isolated colonic disease. This may allow for a more optimized approach to clinical care and scientific research for CD.

Lymphocytes within the intestinal epithelial layer (IEL) in mammals have unique composition compared with their counterparts in the lamina propria. Little is known about the role of some of the key colonic IEL subsets, such as TCRαβ+CD8+ T cells, in inflammation. We have recently described liver-enriched innate-like TCRαβ+CD8αα regulatory T cells, partly controlled by the non-classical MHC molecule, Qa-1b, that upon adoptive transfer protect from T cell–induced colitis. In this study, we found that TCRαβ+CD8αα T cells are reduced among the colonic IEL during inflammation, and that their activation with an agonistic peptide leads to significant Qa-1b–dependent protection in an acute model of colitis. Cellular expression of Qa-1b during inflammation and corresponding dependency in peptide-mediated protection suggest that Batf3-dependent CD103+CD11b− type 1 conventional dendritic cells control the protective function of TCRαβ+CD8αα T cells in the colonic epithelium. In the colitis model, expression of the potential barrier-protective gene, Muc2, is enhanced upon administration of a Qa-1b agonistic peptide. Notably, in steady state, the mucin metabolizing Akkermansia muciniphila was found in significantly lower abundance amid a dramatic change in overall microbiome and metabolome, increased IL-6 in explant culture, and enhanced sensitivity to dextran sulfate sodium in Qa-1b deficiency. Finally, in patients with inflammatory bowel disease, we found upregulation of HLA-E, a Qa-1b analog with inflammation and biologic non-response, in silico, suggesting the importance of this regulatory mechanism across species.

Background Inflammatory bowel diseases (IBD), including ulcerative colitis (UC) and Crohn’s disease (CD), affect ~1% of the people in the United States. SAMP1/YitFcs mice are a model of CD with terminal ileitis which is rare in other animal models of IBD. Switch of cell energy metabolism towards aerobic glycolysis is a hallmark of inflammation and has been implicated in immune-mediated diseases. Thus, we sought to determine how energy metabolism is altered in the SAMP mice. Methods Glucose metabolism in vivo was determined by 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET). Tissue taking up the 18F-FDG were collected for histology. Metabolic phenotype of activated B and CD4+ T lymphocytes isolated from mesenteric lymph nodes of control and SAMP mice was evaluated by extracellular flux analysis (SeaHorse). To relate the SAMP model to human disease, normal and inflamed ileum from mice and humans were assayed by RNAseq focusing on metabolism-related genes. Results PET scans showed a varying tissue distribution of 18F-FDG uptake in SAMP mice, including ileum, salivary glands and kidneys which all had histological evidence of inflammation. Compared to control, both SAMP B and T cells displayed an increase in glycolysis and oxidative phosphorylation (OXPHOS) rates which is supported by an overall increase in genes related to glucose metabolism, TCA cycle, OXPHOS and fatty acid oxidation in the ileum. Conclusion SAMP mice have a multi-organ immune-mediated disease relying on an increase in cell energy metabolism. Therefore, targeting aerobic glucose metabolism to limit inflammation emerges as a new strategy for CD treatment.

Background: Vedolizumab, an α4β7 integrin antagonist, is an effective therapy for Crohn’s disease (CD). Biomarkers are needed to guide therapy and predict outcomes. This study evaluated biomarker concentrations and outcomes in patients with CD undergoing vedolizumab treatment. Methods: Sera at weeks 0, 2, 6, 14, and ⩾26 were collected from vedolizumab-treated, refractory CD patients. Concentrations of soluble (s)-Vascular Cell Adhesion Molecule (VCAM)-1, s-Intercellular Cell Adhesion Molecule (ICAM)-1, s-Mucosal Addressin Cell Adhesion Molecule (MAdCAM)-1, and s-α4β7 integrin were evaluated for associations with achieving endoscopic remission. Results: A total of 22 patients with CD were included. In all patients, s-MAdCAM-1 decreased significantly and s-α4β7 increased compared with baseline. s-VCAM-1 and s-ICAM-1 changed differentially in patients who achieved remission. At week 6, median s-VCAM-1 (859.6 ng/ml versus 460.3 ng/ml, p = 0.03) and s-ICAM-1 (545.7 ng/ml versus 286.2 ng/ml, p = 0.03) concentrations were higher in patients who achieved endoscopic remission compared with those who did not, and similar differences were observed for s-ICAM-1 concentrations in patients who achieved clinical remission, compared with those who did not (669.1 ng/ml versus 291.0 ng/ml, p = 0.04). Week 14 s-α4β7 concentrations were lower in patients who achieved endoscopic remission, compared with those who did not (7.5 ng/ml versus 17.6 ng/ml, p = 0.020). Conclusion: In all vedolizumab-treated CD patients, s-MAdCAM-1 decreased significantly and s-α4β7 increased. However, higher concentrations of s-ICAM-1 and s-VCAM-1 at week 6 and lower concentrations of s-α4β7 at week 14 differentiated patients who achieved endoscopic remission. These findings may help identify early predictors of response to vedolizumab treatment in patients with CD. Further validation in less refractory CD patients is needed.

Summary Sands et al. expand the therapeutic potential of anti-IL-12/IL-23 blockade in IBD, by demonstrating a clear clinical benefit of ustekinumab as induction and maintenance therapy for ulcerative colitis (UC). The UNIFI trial had a double-blind, placebo-control design and consisted of an 8-week induction and a 44-week randomized-withdrawal maintenance trial. Patients with active, moderate-to-severe UC (total Mayo score of 6-12 with endoscopic subscore of ≥2 via central reading) were recruited from 244 centers worldwide. Patient characteristics were similar across groups in the induction and maintenance arms. Half of the patients who were randomized for the induction trial reported a history of treatment failure with biologics, among whom, 98.8% had failed at least one TNF antagonist, 32.6% both a TNF antagonist and vedolizumab, and 1.2% vedolizumab only.

BACKGROUND: Vedolizumab inhibits α4β7-mediated lymphocyte trafficking and is effective in ulcerative colitis (UC). This study evaluated drug and biomarker concentrations and patient outcomes during vedolizumab treatment in UC. METHODS: Prospectively scored maintenance clinical (26.5 weeks; interquartile range [IQR], 16.3–37.0 weeks) and endoscopic (23.5 weeks; IQR, 16.8–35.6 weeks) outcomes were compared with serum vedolizumab concentrations, antivedolizumab antibodies, and serum biomarkers at baseline and weeks 2, 6, 14, and 26. A linear mixed-effects model compared biomarker trajectories over time between clinical and endoscopic remitters and nonremitters. RESULTS: Thirty-two patients were included. Soluble (s)–tumor necrosis factor (TNF)–α, s-α4β7, s-mucosal addressin cell adhesion molecule (s-MAdCAM-1), and s-amyloid A (s-AA) significantly changed with treatment. A linear mixed-effects model demonstrated that s-α4β7 (P = 0.044) increased and s-MAdCAM-1 (P = 0.006) and s-vascular cell adhesion molecule-1 (s-VCAM-1, P = 0.001) decreased more rapidly in patients achieving clinical remission in maintenance. S-MAdCAM-1 (P = 0.005), s-intracellular adhesion molecule-1 (ICAM-1; P = 0.014), s-VCAM-1 (P < 0.001), and s-TNF (P = 0.052) decreased more rapidly in endoscopic remitters. In clinical remitters, higher week 14 (20.3 ng/mL vs 6.0 ng/mL; P = 0.013) and week 26 (14.1 ng/mL vs 8.6 ng/mL; P = 0.05) s-α4β7 were observed. In endoscopic remitters, week 2 (6.7 pg/mL vs 17.8 pg/mL; P = 0.038) and week 6 (3.9 pg/mL vs 15.6 pg/mL; P = 0.005) s-TNF and week 14 s-VCAM (589.1 ng/mL vs 746.0 ng/mL; P = 0.05) were lower. CONCLUSION: Serum biomarkers were associated with outcomes in vedolizumab-treated UC patients. s-α4β7 increased, whereas s-MAdCAM-1, s-VCAM-1, s-ICAM-1, and s-TNF decreased more rapidly in remitters. At individual time points, induction s-TNF and maintenance s-VCAM-1 concentrations were lower, whereas maintenance s-α4β7 concentrations were higher in remitters.

After 20 years of successful targeting of pro-inflammatory cytokines for the treatment of IBD, an alternative therapeutic strategy has emerged, based on several decades of advances in understanding the pathogenesis of IBD. The targeting of molecules involved in leukocyte traffic has recently become a safe and effective alternative. With 2 currently approved drugs (ie, natalizumab, vedolizumab) and several others in phase 3 trials (eg, etrolizumab, ozanimod, anti-MAdCAM-1), the blockade of trafficking molecules has firmly emerged as a new therapeutic era for IBD. We discuss the targets that have been explored in clinical trials: chemokines and its receptors (eg, IP10, CCR9), integrins (eg, natalizumab, AJM300, vedolizumab, and etrolizumab), and its endothelial ligands (MAdCAM-1, ICAM-1). We also discuss a distinct strategy that interferes with lymphocyte recirculation by blocking lymphocyte egress from lymph nodes (small molecule sphingosine-phosphate receptor [S1PR] agonists: fingolimod, ozanimod, etrasimod, amiselimod). Strategies on the horizon include additional small molecules, allosteric inhibitors that specifically bind to the active integrin form and nanovectors that allow for the use of RNA interference in the quest to modulate pro-inflammatory leukocyte trafficking in IBD.

The sphingosine-1-phosphate receptor-1 (S1P1) agonist ozanimod ameliorates ulcerative colitis, yet its mechanism of action is unknown. Here, we examine the cell subsets that express S1P1 in intestine using S1P1-eGFP mice, the regulation of S1P1 expression in lymphocytes after administration of dextran sulfate sodium (DSS), after colitis induced by transfer of CD4+CD45RBhi cells, and by crossing a mouse with TNF-driven ileitis with S1P1-eGFP mice. We then assayed the expression of enzymes that regulate intestinal S1P levels, and the effect of FTY720 on lymphocyte behavior and S1P1 expression. We found that not only T and B cells express S1P1, but also dendritic (DC) and endothelial cells. Furthermore, chronic but not acute inflammatory signals increased S1P1 expression, while the enzymes that control tissue S1P levels in mice and humans with inflammatory bowel disease (IBD) were uniformly dysregulated, favoring synthesis over degradation. Finally, we observed that FTY720 reduced T-cell velocity and induced S1P1 degradation and retention of Naïve but not effector T cells. Our data demonstrate that chronic inflammation modulates S1P1 expression and tissue S1P levels and suggests that the anti-inflammatory properties of S1PR agonists might not be solely due to their lymphopenic effects, but also due to potential effects on DC migration and vascular barrier function.

Algorithms for the diagnosis, management, and follow-up have been proposed for patients hospitalized for inflammatory bowel disease (IBD) colitis flare. The degree to which providers adhere to these algorithms is unknown. This study evaluated the quality of care in IBD patients hospitalized for disease-associated exacerbations and factors correlated with higher degrees of care. Retrospective chart review of 34 patients during 60 admissions to the medicine service for IBD colitis exacerbation between 2005 and 2012 at the Veterans Affairs San Diego Medical Center. Examined factors included laboratory testing, timing of consultation and intravenous steroids, abdominal imaging, endoscopic examination, venous thromboembolism (VTE) prophylaxis, narcotic use, Clostridium difficile and cytomegalovirus testing, symptomatology at discharge, timing of follow-up, and rates of readmission and mortality. Quality of care varied among the factors studied, ranging from 30.5 % for pharmacologic VTE prophylaxis to 84.7 % for gastroenterology consultation within 24 h. Of 60 admissions, 22 % were not tested for C. difficile. Fifteen percent of patients were discharged before meeting commonly used discharge criteria. Eighty percent were seen in clinic at any time post-discharge; 6.7 % were readmitted; 10 % were lost to follow-up; 1.7 % opted for outside follow-up; and 1.7 % expired. The quality of care for patients admitted with IBD colitis flares is variable. These data outline opportunities for improvement, particularly in regard to pain management, VTE prophylaxis, and follow-up. Further studies are needed to test intervention strategies for practice improvement.

The incidence of ulcerative colitis (UC) is increasing worldwide. A proven therapeutic strategy for UC is the inhibition of leukocyte trafficking via blockade of integrin β7. Despite this, the mechanism of action of vedolizumab (anti-α4β7) is poorly defined. Clear definitions of the immune subsets targeted by vedolizumab are essential for understanding the pathogenesis of UC, and development of biological endpoints for assessing treatment efficacy. Methods The IL-10−/− colitis model was crossed with integrin β7 deficient mice, and clinical features and histological scores were recorded. Flow cytometry of B-cell populations was conducted in colonic cell isolations. 16S bacterial sequencing was conducted on intestinal content. Results IL-10−/−β7−/− mice displayed increased mortality compared to IL-10−/− mice at 12 weeks and uniformly developed rectal prolapses. IL-10−/−β7−/− mice displayed increased colonic inflammatory indices (n>10, p6, p Discussion Integrin β7 deficiency results in a worsening of colitis in mice, resulting from a B-cell deficit in the inflamed colon and control the microbiota, via IgA. B-cells are largely ignored in the field of IBD and the potential complications associated with chronic integrin blockade. Our data suggests that the role of integrin β7 on B-cell migration may have important implications on the pathogenesis of colitis in mice and humans.

S1P is a bioactive sphingolipid that participates as a critical regulator of many physiological processes, mainly in lymphocyte egress from lymphoid tissue, mediated by S1P gradients through the activity of S1P lyase (SPL). Inhibition of both S1P-specific receptors and Lyase activity has been shown to improve inflammatory conditions during Crohn’s-like ileitis. In contrast to this, initial observations show acute DSS-induced colitis was aggravated by SPL inhibition. Here we investigate whether the inhibition of Lyase in the intestinal epithelium is the cause of the exacerbation of colitis. To induce global or epithelial cell specific SPL deletion, Gt(rosa)-cre or Villin-cre Sgpl1 transgenic mice were administered with tamoxifen (80 mg/kg) by oral gavage for 5 consecutive days. Then, mice were treated with DSS (2.5%) in drinking water for 7 days. Clinical features and histological scores were recorded. Permeability assays were performed to evaluate integrity of the intestinal epithelium with fluorescein isothiocyanate (FITC)-dextran 4 kDa. Significant differences in the histopathological features (inflammation and injury) in colon were observed between Gt(rosa)Cre+/−/SPL−/− or VillinCre+/−/SPL−/− mice compared to their respective controls (without tamoxifen treatment) (n>10, p10, p In conclusion, in the acute model of DSS-induced colitis the presence of S1P in the intestinal epithelium exacerbates inflammatory conditions, demonstrating that there could be differences in the mechanisms with chronic models of IBD.

Background & Aims As more treatment options for inflammatory bowel diseases become available, it is important to identify patients most likely to respond to different therapies. We created and validated a scoring system to identify patients with Crohn’s disease (CD) who respond to vedolizumab. Methods We collected data from the GEMINI 2 phase 3 trial of patients with active CD treated with vedolizumab for 26 weeks (n = 814) and performed logistic regression analysis to identify factors associated with clinical, steroid-free, and durable remission (derivation set). We used these data to develop a clinical decision support tool, which we validated using data from 366 participants in a separate clinical practice observational cohort of patients with active CD treated with vedolizumab for 26 weeks (the VICTORY cohort). We evaluated the ability of this tool to identify patients in clinical remission or corticosteroid-free remission, or those with mucosal healing (MH), clinical remission with MH, or corticosteroid-free remission with MH after vedolizumab therapy using receiver operating characteristic area under the curve (AUC) analyses. The primary outcome was to develop and validate a list of factors associated with achieving remission by vedolizumab in patients with active CD. Results In the derivation analysis, we identified absence of previous treatment with a tumor necrosis factor antagonist (+3 points), absence of prior bowel surgery (+2 points), absence of prior fistulizing disease (+2 points), baseline level of albumin (+0.4 points per g/L), and baseline concentration of C-reactive protein (reduction of 0.5 points for values between 3.0 and 10.0 mg/L and 3.0 points for values >10.0 mg/L) as factors associated with remission. In the validation set, our model identified patients in clinical remission with an AUC of 0.67, patients in corticosteroid-free remission with an AUC of 0.66, patients with MH with an AUC of 0.72, patients in clinical remission with MH with an AUC of 0.73, and patients in corticosteroid-free clinical remission with MH with an AUC of 0.75. A cutoff value of 13 points identified patients in clinical remission after vedolizumab therapy with 92% sensitivity, patients in corticosteroid-free remission with 94% sensitivity, patients with MH with 98% sensitivity, patients with clinical remission and MH with 100% sensitivity, and patients with corticosteroid-free clinical remission with MH with 100% sensitivity. Conclusions We developed and validated a scoring system to identify patients with CD most likely to respond to 26 weeks of vedolizumab therapy. Further studies are needed to optimize its accuracy in select populations and determine its cost-effectiveness.

BACKGROUND: Novel therapeutics for inflammatory bowel disease (IBD) are under development, yet mechanistic readouts at the tissue level are lacking. Techniques to assess intestinal immune composition could represent a valuable tool for mechanism of action (MOA) studies of novel drugs. Mass cytometry enables analysis of intestinal inflammatory cell infiltrate and corresponding molecular fingerprints with unprecedented resolution. Here, we aimed to optimize the methodology for isolation and cryopreservation of cells from intestinal tissue to allow for the potential implementation of mass cytometry in MOA studies. METHODS: We investigated key technical issues, including minimal tissue requirements, cell isolation protocols, and cell storage, using intestinal biopsies and peripheral blood from healthy individuals. High-dimensional mass cytometry was employed for the analyses of biopsy-derived intestinal cellular subsets. RESULTS: Dithiothreitol and mechanical dissociation decreased epithelial cell contamination and allowed for isolation of adequate cell numbers from 2 to 4 colonic or ileal biopsies (6 × 10(4)±2 × 10(4)) after a 20-minute collagenase digestion, allowing for reliable detection of most major immune cell subsets. Biopsies and antibody-labeled mononuclear cells could be cryopreserved for later processing and acquisition (viability > 70%; P < 0.05). CONCLUSIONS: Mass cytometry represents a unique tool for deep immunophenotyping intestinal cell composition. This technique has the potential to facilitate analysis of drug actions at the target tissue by identifying specific cellular subsets and their molecular signatures. Its widespread implementation may impact not only IBD research but also other gastrointestinal conditions where inflammatory cells play a role in pathogenesis.

The recruitment of leukocytes from peripheral blood into the intestine is required for the maintenance of intestinal health and protection from microbial insult. However, during immune-mediated gastrointestinal conditions (e.g., inflammatory bowel disease (IBD), celiac disease), the recruitment process becomes dysregulated. Several families of molecules regulate the influx of these cells into immune sites both during homeostasis and inflammation. Interference with some of these molecules has already shown efficacy in the clinics and antibodies that target the molecules involved have been approved by the FDA for use in IBD. In this chapter, we discuss basic aspects of the diverse families of relevant molecules that mediate the leukocyte adhesion cascade under physiological and inflammatory conditions to relevant immune compartments. Finally, we discuss the translational applications of targeting-specific steps of the leukocyte adhesion cascade for therapeutic purposes in human IBD.

The gut-associated lymphoid tissues are the guardians of the enteric immune system and integrate dietary and microbial stimuli to maintain immunologic tolerance. However, during periods of persistent chronic inflammation, such as in Crohn’s disease (CD), a dysfunctional lymphatic system is a pathologic hallmark. Indeed, the predominant histopathologic features of CD are lymphocytic lymphangitis, occluded lymphatic vessels, and inflammatory granulomas. These trademark features of chronic disease are found in or around ectopic tertiary lymphoid tissues (TLT) in the inflamed lamina propria (Gut 2008;57:1-4). In addition, the presence of TLT at the base of aphthous ulcers is the earliest endoscopically evident lesion in CD and their appearance heralds recurrent disease within the neoterminal ileum after ilectomy (Gut 1984;25:665-672). To date, the function of intestinal TLT and their impact on the etiology and pathogenesis of CD remains enigmatic, with limited experimental evidence as to their role. How TLT integrate into the pathophysiology of CD remains a critical question, yet clinical investigation into their development and function remains limited. Randolph et al aimed to assess the integrity of mesenteric lymphatic vasculature in CD. First, they confirmed the previous findings generated from immunopathologic studies of intestinal mucosa, indicating defective lymphatic function during active disease. To achieve this, patent blue dye was injected into the serosa of ileal loops before surgical resection, highlighting afferent lymphatic vessels draining the lamina propria. This technique nicely demonstrated a deviation of normal lymphatic vessels in active CD, compared with non-CD counterparts and indicated a remodeling of the vasculature in the mesentery. Next, they used a 3-dimensional system to image whole mount sections from a patient cohort undergoing ilectomy for stricturing CD (to obtain cm3 tissue coverage). Surprisingly, this work revealed advanced remodeling of the lymphatic vascular tracks, with the presence of ectopic lymphoid follicles within the collecting vessel line. A border of adipocytes and no evident capsule, suggesting that these organized structures were not sentinel lymph nodes but TLT instead. The work by Randolph et al highlights that, although most studies have reported on lymphatic capillaries in the intestinal wall, where collecting vessels remove solutes and immune cells, the primary functional site of lymphatic dysfunction may be the larger vessels in the mesentery, which interface with sentinel lymph nodes.

The medical management of idiopathic inflammatory bowel disease (IBD) has historically been based upon the use of broad-spectrum anti-inflammatory drugs such as corticosteroids and thiopurines. Recently, the identification of novel mechanisms central to the pathophysiology of IBD has provided more specific targets, including inhibition of leukocyte trafficking to the gut. In this article, we discuss the molecular biology of intestinal leukocyte trafficking and review the emerging therapies that target this process, including vedolizumab, natalizumab, etrolizumab, PF-547659, alicaforsen, efalizumab, and emerging members of this class.

BACKGROUND The inflammatory bowel diseases (IBD) can affect various segments of the gastrointestinal tract, and the biology behind regional differences in disease remains poorly understood, in part due to a lack of understanding of regional variation of the particular cell subsets present. By utilizing mass cytometry, our objective was to identify regional differences in the immune composition of the digestive tract in healthy individuals. METHOD Intestinal pinch biopsies were obtained from the following sites of healthy individuals (n=10); duodenum, terminal ileum, ascending colon, transverse colon, descending colon, and rectum. Immune cells were isolated from biopsies and stained with a panel of 37 markers for analysis using mass cytometry. RESULTS Marked variations in immune cell composition were observed along the digestive tract, in particular T and B lymphocytes. Increased abundance of T lymphocytes (>30% of total CD45+ cells) was identified in the duodenum and terminal ileum, whereas B lymphocytes became more abundant (>30% of total CD45+ cells) towards the distal end of the tract. In addition, intestinal homing molecules displayed variation at each site; integrin α4β7, a target for IBD therapeutic intervention, was increasingly expressed in the terminal ileum and ascending colon, compared with the descending colon (Mean 40% vs 25% abundance, n=10, p CONCLUSIONS Mass cytometry has the ability to identify and characterize numerous distinct immune subsets throughout the intestinal mucosa, allowing a deep understanding of regional differences in immune composition. This understanding may shed light on the pathogenesis of IBD and allow standardization of intestinal sampling during the evaluation of therapeutics.

The interleukin 1 (IL-1) family consists of eleven proteins, which are further organized into 3 subfamilies. IL-1α and IL-1β, which belong to the IL-1 subfamily, have been long recognized as integral components of innate immune processes. As such they are implicated in the pathogenesis of several inflammatory diseases, including Inflammatory Bowel Disease (IBD). Moreover, therapeutic neutralization of IL-1β and now also of IL-1α are integrated into clinical practice. Bersudsky et al. aimed to dissect the specific roles of IL-1α and IL-1β during acute colitis and restitution, following injury by administration of dextran sulfate sodium (DSS) in mice (Bersudsky, M, Luski, L, Fishman, D et al. Gut 2014; 63:598). The two cytokines exerted opposite roles, as indicated by the differential natural course of acute DSS-colitis in mice deficient for IL-1α or IL-1β. IL-1α KO mice demonstrated attenuated colitis with no mortality and significantly less weight loss, fecal bleeding and histological damage. Furthermore, epithelial restitution was intact, with intense epithelial cell proliferation, preservation of barrier function and abundant expression of the tight junction protein, claudin-3. In sharp contrast, mice deficient for IL-1β had severe colitis as well as lethality. Significant histological damage was still present 7 days post-DSS cessation, indicating failure of healing mechanisms, such as defective epithelial proliferation, increased epithelial permeability and absent claudin-3 signal by immunohistochemistry. These findings clearly point to a pro-inflammatory role of IL-1α and a protective role of IL-1β during acute inflammation/repair of the gut mucosa. Accordingly, neutralization of IL-1α via an anti-mouse IL-1α-specific monoclonal antibody led to decreased severity of DSS-colitis in wild-type mice, whereas administration of the IL-1-receptor antagonist (IL-1Ra), which blocks both IL-1α and IL-1β, had no ameliorating effect on colitis.

Crohn's disease (CD) is a chronic inflammatory disorder of the gastrointestinal tract (GI) for which treatments with immunosuppressive drugs have significant side-effects. Consequently, there is a clinical need for site-specific and non-toxic delivery of therapeutic genes or drugs for CD and related disorders such as inflammatory bowel disease. The aim of this study was to validate a gene delivery platform based on ultrasound-activated lipid-shelled microbubbles (MBs) targeted to inflamed mesenteric endothelium in the CD-like TNFΔARE mouse model. MBs bearing luciferase plasmid were functionalized with antibodies to MAdCAM-1 (MB-M) or VCAM-1 (MB-V), biomarkers of gut endothelial cell inflammation and evaluated in an in vitro flow chamber assay with appropriate ligands to confirm targeting specificity. Following MB retro-orbital injection in TNFΔARE mice, the mean contrast intensity in the ileocecal region from accumulated MB-M and MB-V was 8.5-fold and 3.6-fold greater, respectively, compared to MB-C. Delivery of luciferase plasmid to the GI tract in TNFΔARE mice was achieved by insonating the endothelial cell-bound agents using a commercial sonoporator. Luciferase expression in the midgut was detected 48 h later by bioluminescence imaging and further confirmed by immunohistochemical staining. The liver, spleen, heart, and kidney had no detectable bioluminescence following insonation. Transfection of the microcirculation guided by a targeted, acoustically-activated platform such as an ultrasound contrast agent microbubble has the potential to be a minimally-invasive treatment strategy to ameliorate CD and other inflammatory conditions.

Integrins are activatable adhesion and signaling molecules. Of the 24 known human integrins, three are currently targeted therapeutically by monoclonal antibodies, peptides or small molecules. The platelet αIIbβ3 integrin is targeted by Abciximab, Eptifibatide and Tirofiban, all with indications for preventing thrombotic complications after percutaneous coronary interventions. The lymphocyte α4β1 and α4β7 integrins are targeted by Natalizumab with indications in multiple sclerosis and Crohn’s disease. Although efficacious, use of this antibody is limited by a rare but serious complication, progressive multifocal leukoencephalopathy. Vedolizumab is an antibody to a combinatorial epitope in α4β7 that is approved for use in patients with Crohn’s disease or ulcerative colitis in the United States, Canada and Europe. Progressive multifocal leukoencephalopathy has not been observed in the clinical trials or clinical use of vedolizumab. New antibodies and small molecules targeting β7 integrins (α4β7 and αEβ7) and MAdCAM-1 are in clinical development for treatment of these inflammatory bowel diseases. Overall, integrin-based therapeutics have shown clinically significant benefits in many patients, leading to continued medical interest in the further development of novel integrin inhibitors. Of note, almost all integrin antagonists in use or in late-stage clinical trials target the ligand binding site, or the ligand itself.

Background The earliest endoscopically-evident lesion in Crohn9s disease is the aphthous ulcer, which develops over ectopic lymphoid tissues (ie, inducible lymphoid follicles (ILF), tertiary lymphoid tissue (TLT)) in the chronically inflamed intestine. ILF/TLT are induced within effector sites by homeostatic lymphoid chemokines, but their role in the development of intestinal ILF/TLT and in the pathogenesis of Crohn9s disease is poorly understood. Design Using a mouse model of Crohn9s-like ileitis (TNF∆ARE) which develops florid induction of ILF/TLT within its terminal ileum, the contribution of the CCR7/CCL19/CCL21 chemokine axis during the development of TLT and its role in disease pathogenesis were assessed. Results Both CCL19 and CCL21 were increased within the inflamed ileum of TNF∆ARE mice, which resulted in CCR7 internalisation and impaired T cell chemotaxis. ILF/TLT were a major source of CCL19 and CCL21 and increased local synthesis, augmented recruitment/retention of effector, naive and central memory T cell subsets within the inflamed ileum. Immunoblockade of CCR7 resulted in further effector T cell retention and exacerbation of ileitis. Conclusions Induction of ILF/TLT in the chronically inflamed intestine alters the homeostatic CCL19-CCL21 lymphoid-chemokine gradient and increases recruitment/retention of effector CCR7+ T cell subsets within the terminal ileum, contributing to the perpetuation of chronic inflammation. Thus, blockade of CCR7 or its ligands might result in deleterious consequences for subjects with chronic inflammatory diseases.

Intestinal remodeling and stricture formation is a complication of inflammatory bowel disease (IBD) that often requires surgical intervention. Although eosinophils are associated with mucosal remodeling in other organs and are increased in IBD tissues, their role in IBD-associated remodeling is unclear. Histological and molecular features of ileitis and remodeling were assessed using immunohistochemical, histomorphometric, flow cytometric, and molecular analysis (real-time RT-PCR) techniques in a murine model of chronic eosinophilic ileitis. Collagen protein was assessed by Sircol assay. Using a spontaneous eosinophilic Crohn’s-like mouse model SAMP1/SkuSlc, we demonstrate an association between ileitis progression and remodeling over the course of 40 weeks. Mucosal and submucosal eosinophilia increased over the time course and correlated with increased histological inflammatory indices. Ileitis and remodeling increased over the 40 weeks, as did expression of fibronectin. CCR3-specific antibody-mediated reduction of eosinophils resulted in significant decrease in goblet cell hyperplasia, muscularis propria hypertrophy, villus blunting, and expression of inflammatory and remodeling genes, including fibronectin. Cellularity of local mesenteric lymph nodes, including T- and B-lymphocytes, was also significantly reduced. Thus, eosinophils participate in intestinal remodeling, supporting eosinophils as a novel therapeutic target.

Lymphocytes involved in intestinal immune response are found in organized immune inductive sites of the gut-associated lymphoid tissues (GALT) such as Peyer's patches (PP), mesenteric lymph nodes (MLN) and diffuse effector sites of gut epithelium and lamina propria (LP). beta(7) integrins are responsible for efficient trafficking and retention of lymphocytes in these sites. Naive and effector lymphocytes use alpha(4)beta(7) integrin to extravasate from blood to gut mucosal tissues of GALT, MLN and LP via interactions with Mucosal Addressin Cell Adhesion Molecule-1 (MAdCAM-1). The alpha(E)beta(7) integrin facilitates retention of effector and memory lymphocytes in the gut epithelial layer via interactions with E-cadherin. Mucosal dendritic cells (DCs) regulate the expression of the gut homing receptors alpha(4)beta(7) integrin and the chemokine receptor CCR9 on activated effector and regulatory lymphocytes in a retinoic acid-dependent manner. CD103 (alpha(E) integrin) identifies a subset of mucosal DCs in MLN and small intestine LP that have an enhanced ability to induce gut-tropic receptors on responding lymphocytes. The interactions between beta(7) integrin and their ligands are also implicated in the pathogenesis and progression of inflammatory bowel diseases (IBDs), intestinal parasitic infections and graft-versus-host diseases. During intestinal inflammation, beta(7) integrin-dependent and -independent pathways contribute to lymphocytes recruitment to the intestinal tissues and disease pat-hogenesis. Recent works have explored the potential of therapeutic targeting of alpha(4) and beta(7) integrins in IBDs. Here, we review the current understanding of the role of beta(7) integrins in intestinal lymphocyte trafficking and retention in health and disease.

Background & Aims Lymphocyte recruitment to sites of inflammation requires the sequential engagement of adhesion molecules and chemokine receptors. In the current studies we analyzed the role of CD44 for the development of chronic small-intestinal inflammatory infiltrates in vivo. Methods By using a tumor necrosis factor (TNF)-driven model of chronic ileitis (ie, B6.129P-TNF ΔAU-rich element [ARE] ) that recapitulates many features of Crohn's disease, we noticed dynamic changes in the expression and functional state of CD44 and its ligand hyaluronan via enzyme-linked immunosorbent assay, real-time reverse-transcription polymerase chain reaction, immunohistochemistry, and flow cytometry. In addition, we assessed the role of lymphocyte populations during induction of ileitis through adoptive transfer studies, and generated CD44-deficient TNFΔARE mice to assess the role of CD44 for development of ileitis. Results Soluble hyaluronan levels and expression of hyaluronan synthase-1 were increased in TNFΔARE mice. This coincided with increased expression of CD44 (including variant 7) and reactivity towards hyaluronan on CD4 + T cells. CD44 was spatially colocalized with the gut-homing integrin α 4 β 7 , spatially linking lymphocyte rolling with arrest. These cells had an effector phenotype because they lacked L-selectin and a higher proportion in diseased mice produced TNF and interleukin-2 compared with wild-type littermates. Lastly, CD4 + but not CD8 + T cells conferred ileitis to RAG −/− recipients and deficiency of one or both alleles of the CD44 gene resulted in attenuation of the severity of ileitis in TNFΔARE mice. Conclusions Our findings support an important role of CD44 expressed by CD4 + and CD8 + for development of ileitis mediated by TNF overproduction.

Recruitment of lymphocytes to sites of inflammation requires the sequential engagement of adhesion molecules and chemokine receptors. Of these, the lectin-like molecule CD44 has been particularly implicated in inflammatory trafficking. Using a TNF-driven model of chronic ileitis (i.e., B6.129P-TnfΔARE mice) that recapitulates many features of Crohn’s disease, we demonstrate dynamic changes in the expression and functional state of CD44 on CD8+ T cells. These cells coexpress CD44 and L-selectin, giving them a surface phenotype similar to that of central memory T cells. Yet functionally they exhibit the phenotype of effector T cells, because they produce IFN-γ. Unexpectedly, depletion of the CD8+ population had no effect on the severity of ileitis. Further analyses showed a second CD8+ population that lacked CD44, but expressed CD103, produced TGF-β, inhibited the proliferation of CD4+ in vitro, and attenuated adoptively transferred ileitis in vivo, most likely counteracting the proinflammatory role of the CD44high subset. Collectively, these data suggest that the presence or absence of CD44 and CD103 on the CD8+ lymphocyte surface defines functionally distinct subsets of CD8+ T cells in vivo. These inflammation-driven populations exert distinct roles during the development of chronic ileitis, and influence the balance of effector and regulatory functions in the chronically inflamed small intestine.

BackgroundThe ability to measure the expression of proinflammatory cytokines from intestinal biopsies in patients with Crohn's disease in an accurate and reproducible way is critical for proof-of-concept and mechanism-of-action trials; however, the number of biopsies from a segment of the ileum or colon required to yield reproducible results has not been rigorously evaluated. We examined intestinal biopsies from patients with Crohn's disease to validate methods for detecting changes in inflammatory gene expression.MethodsTo evaluate the reproducibility of gene expression measurements, intestinal biopsies were obtained from designated segments from 6 healthy controls, 6 patients with active Crohn's disease, and 6 patients with inactive Crohn's disease. Disease activity was based on the simple endoscopic score for Crohn's disease. Expression of 7 proinflammatory genes was measured from each biopsy using quantitative polymerase chain reaction. Using a linear mixed effects model, the power to detect transcriptional changes corresponding to active and inactive Crohn's disease was calculated.ResultsTotal simple endoscopic score for Crohn's disease score corresponds with expression of most inflammatory biomarkers. For most genes, 2 to 5 biopsies are needed to reduce sampling error to

The regulation of T cell and DC retention and lymphatic egress within and from the intestine is critical for intestinal immunosurveillance; however, the cellular processes that orchestrate this balance during IBD remain poorly defined. With the use of a mouse model of TNF-driven Crohnˈs-like ileitis (TNFΔARE), we examined the role of CCR7 in the control of intestinal T cell and DC retention/egress during experimental CD. We observed that the frequency of CCR7-expressing TH1/TH17 effector lymphocytes increased during active disease in TNFΔARE mice and that ΔARE/CCR7−/− mice developed exacerbated ileitis and multiorgan inflammation, with a marked polarization and ileal retention of TH1 effector CD4+ T cells. Furthermore, adoptive transfer of ΔARE/CCR7−/− effector CD4+ into lymphopenic hosts resulted in ileo-colitis, whereas those transferred with ΔARE/CCR7+/+ CD4+ T cells developed ileitis. ΔARE/CCR7−/− mice had an acellular draining MLN, decreased CD103+ DC, and decreased expression of RALDH enzymes and of CD4+CD25+FoxP3+ Tregs. Lastly, a mAb against CCR7 exacerbated ileitis in TNFΔARE mice, phenocopying the effects of congenital CCR7 deficiency. Our data underscore a critical role for the lymphoid chemokine receptor CCR7 in orchestrating immune cell traffic and TH1 versus TH17 bias during chronic murine ileitis.

Background & Aims: CCL25 mediates the homeostatic recruitment of CCR9-expressing lymphocytes to the small intestine, but the function of this chemokine/receptor pair during chronic small intestinal inflammation has yet to be determined. Furthermore, although clinical trials to evaluate the efficacy of targeting the CCL25/CCR9 axis for the treatment of Crohn's disease are being conducted, preclinical data in animal models of IBD are lacking. Methods: In the current studies, we investigated the expression of CCL25 and CCR9 as a function of disease progression in a spontaneous murine model of chronic ileitis (SAMP1/YitFc) using flow cytometry, real-time reverse-transcription polymerase chain reaction, enzyme-linked immunosorbent assay, and immunohistochemistry. In addition, we assessed the functional role of the axis in the overall disease process through therapeutic studies that target the chemokine or the receptor during early and late disease. Results: The percentage of CCR9-expressing lymphocytes increased during early disease, accompanied by the appearance of a population of CCR9 high lymphocytes, predominantly within CD8 + T cells. Yet different from patients with primary sclerosing cholangitis, the expression of CCL25 remained restricted to the small intestine, even in mice with inflammation of the biliary tree. Neutralization of the receptor or the chemokine attenuated early disease but showed no therapeutic efficacy during the later stages, when overall CCR9 expression decreased and the CCR9 high population was absent. Conclusions: Our studies show that the role of this chemokine axis is not limited to homeostatic recruitment, as previously believed. However, these molecules appear to play their most crucial role during the early stages of chronic murine ileitis.

L-selectin ligands might be relevant for inflammatory cell trafficking into the small intestine in a spontaneous model of chronic ileitis (i.e., SAMP1/YitFc mice). Immunoblockade of peripheral node addressin or mucosal addressin cell adhesion molecule 1 failed to ameliorate ileitis, whereas P-selectin glycoprotein ligand 1 (PSGL-1) neutralization attenuated both the adoptively transferred and spontaneous disease. PSGL-1 was detected in venules of mesenteric lymph node and small intestine by immunohistochemistry and confirmed by real-time reverse transcription polymerase chain reaction and flow cytometry. In addition, reconstitution of wild-type mice with PSGL-1−/− bone marrow demonstrated that PSGL-1 messenger RNA and PSGL-1 protein expression remained on endothelium, localized within mesenteric lymph node and small intestine. Endothelial PSGL-1 bound P-selectin–IgG and its blockade or genetic deletion altered the recruitment of lymphocytes to the small intestine, as revealed by intravital microscopy and homing studies. Endothelial expression of PSGL-1 adds a new dimension to the various cellular interactions involved in small intestinal recruitment. Thus, the multiple roles of PSGL-1 may explain why targeting this single adhesion molecule results in attenuation of chronic murine ileitis, a disease previously resistant to antiadhesion molecule strategies.

L -selectin (CD62L) is an adhesion molecule expressed on most leukocytes. This article describes recent findings of L -selectin's role in the recruitment of T cells to sites of inflammation and its contribution to the acquisition of immunologic memory. We discuss the regulation of L -selectin expression during and after the activation of T cells and its physiological function during the course of inflammation. Different disease models and current approaches for drug development are reviewed.

Adenosine has been implicated as an important regulator of the inflammatory response. Four subtypes of adenosine receptors (A 1 , A 2A , A 2B , and A 3 ) have been described, of which A 2A potentially inhibits inflammation. The aim of this study was to investigate the role of A 2A in mucosal inflammation by administering a selective A 2A agonist (ATL-146e) to experimental models of inflammatory bowel disease.The anti-inflammatory effects of ATL-146e were studied in the acute and chronic rabbit formalin-immune complex models of colitis and the SAMP1/YitFc mouse model of spontaneous ileitis.ATL-146e significantly reduced the acute inflammatory index and tissue necrosis compared with vehicle ( P.01) in the acute model of rabbit immune colitis. In the chronic rabbit immune colitis model, ATL-146e significantly suppressed inflammatory cell infiltration into the colonic mucosa ( P.05) and prevented mortality. The administration of ATL-146e significantly decreased the chronic inflammatory index ( P.01) and villus distortion index ( P.01) in the ileum of SAMP1/YitFc mice, and ameliorated adoptively transferred ileitis in severe combined immunodeficient mice injected with CD4 + T cells from SAMP1/Yit mice ( P.05). Tumor necrosis factor, interferon gamma, and interleukin 4 concentrations were significantly suppressed by ATL-146e treatment in supernatants from cultures of mesenteric lymph node cells of SAMP1/YitFc mice ( P.05 vs vehicle-treated mice).A 2A adenosine receptor activation by ATL-146e significantly reduced inflammation in the intestinal mucosa. This effect was associated with decreased leukocyte infiltration and inhibition of proinflammatory cytokines. Activation of A 2A by selective agonism may therefore serve as a novel therapy for the treatment of inflammatory bowel disease.

CD4+ T cells are essential for development and perpetuation of Crohn's disease, a chronic immune-mediated condition that affects primarily the small intestine. Using novel models of Crohn's disease-like ileitis (i.e., SAMP1/YitFc and CD4+ T cell transfer models), we have begun to understand the adhesive pathways that mediate lymphocyte trafficking to the chronically inflamed small bowel. Expansion of the CD4/beta7+ population and increased mucosal addressin cell adhesion molecule-1 (MAdCAM-1) expression were observed within the intestinal lamina propria with disease progression. However, Ab blockade of the beta7 integrin, the alpha4beta7 heterodimer, MAdCAM-1, or L-selectin did not attenuate inflammation. Blockade of two pathways (L-selectin and MAdCAM-1 or alpha4 integrins) was required to improve ileitis. Further analyses showed that 55 +/- 7% of the mesenteric lymph node alpha4beta7+CD4 expressed L-selectin. These L-selectin+ T cells were the main producers of TNF-alpha and the predominant ileitis-inducing subpopulation. Mechanistically, combined blockade of L-selectin and MAdCAM-1 depleted the intestinal lamina propria of CD4+ T cells that aberrantly coexpressed alpha4beta7 and alpha4beta1 integrins, markedly decreasing local production of TNF-alpha and IFN-gamma. Thus, pathogenic CD4+ T cells not only use the physiologic alpha4beta7/MAdCAM-1 pathway, but alternatively engage alpha4beta1 and L-selectin to recirculate to the chronically inflamed small intestine.

Individuals with α1-antitrypsin (α1-AT) deficiency are at risk for early-onset destructive lung disease as a result of insufficient lower respiratory tract α1-AT and an increased burden of neutrophil products such as elastase. Human neutrophil peptides (HNP), the most abundant protein component of neutrophil azurophilic granules, represent another potential inflammatory component in lung disease characterized by increased numbers of activated or deteriorating neutrophils. The purpose of this study was to determine the role of HNP in lower respiratory tract inflammation and destruction occuring in α1-AT deficiency. α1-AT-deficient individuals ( n = 33) and healthy control subjects ( n = 21) were evaluated by bronchoalveolar lavage. HNP concentrations were significantly higher in α1-AT-deficient individuals (1,976 ± 692 vs. 29 ± 12 nM, P < 0.0001), and levels correlated with markers of neutrophil-mediated lung inflammation. In vitro, HNP produced a dose-dependent cytotoxic effect on alveolar macrophages and stimulated production of the potent neutrophil chemoattractants leukotriene B4and interleukin-8 by alveolar macrophages, with a 6- to 10-fold increase in chemoattractant production over negative control cultures ( P < 0.05). A synergistic effect was noted between HNP and neutrophil elastase with regard to leukotriene B4production. Importantly, the proinflammatory effects of HNP were blocked by α1-AT. HNP likely play an important role in amplifying and maintaining neutrophil-mediated inflammation in the lungs.

We describe here the immunologic characterization of a new mouse strain, SAMP1/Yit, which spontaneously develops a chronic intestinal inflammation localized to the terminal ileum. The resulting ileitis bears a remarkable resemblance to human Crohn’s disease. This strain of mice develops discontinuous, transmural inflammatory lesions in the terminal ileum with 100% penetrance by 30 weeks of age. The intestinal inflammation is characterized by massive infiltration of activated CD4+ and CD8α+TCRαβ+ T cells into the lamina propria and is accompanied by a dramatic decrease in the intraepithelial lymphocyte CD8α+TCRγδ+/CD8α+TCRαβ+ ratio. The results of adoptive transfer experiments strongly suggest that CD4+ T cells that produce a Th1-like profile of cytokines, e.g., IFN-γ and TNF, mediate the intestinal inflammation found in SAMP1/Yit mice. In addition, pretreatment of adoptive transfer recipients with a neutralizing anti-TNF antibody prevents the development of intestinal inflammation, suggesting that TNF plays an important role in the pathogenesis of intestinal inflammation in this model. To our knowledge, these data provide the first direct evidence that Th1-producing T cells mediate intestinal inflammation in a spontaneous animal model of human Crohn’s disease.

Dysregulated recruitment of leukocytes into the intestine is a characteristic feature of IBD. Several families of molecules regulate the influx of these cells into sites of inflammation within the gastrointestinal tract. Pharmacological blockade of interactions between molecules that mediate the formation of stable bonds (integrins) and their endothelial ligands has already shown clinical efficacy. Antibodies that target participant molecules have been approved by the US Federal Drug Administration for use in Crohn's, multiple sclerosis (MS) (i.e. natalizumab) and psoriasis (i.e. efalizumab). A more recent additional family of drugs, which might also interfere with lymphocyte traffic (i.e. sphingosine-1- phosphate receptor agonists: fingolimod) is in clinical use for MS and just recently entered the clinical trial stage for ulcerative colitis. In the present review we discuss basic aspects of clinically relevant molecules and compile the clinical studies that support the targeting of specific steps of the leukocyte adhesion cascade for therapeutic purposes in IBD.