William A. Faubion

Toxic bile salts induce rodent hepatocyte apoptosis via direct activation of Fas

Cholestatic liver injury appears to result from the induction of hepatocyte apoptosis by toxic bile salts such as glycochenodeoxycholate (GCDC). Previous studies from this laboratory indicate that cathepsin B is a downstream effector protease during the hepatocyte apoptotic process. Because caspases can initiate apoptosis, the present studies were undertaken to determine the role of caspases in cathepsin B activation. Immunoblotting of GCDC-treated McNtcp.24 hepatoma cells demonstrated cleavage of poly(ADP-ribose) polymerase and lamin B1 to fragments that indicate activation of effector caspases. Transfection with CrmA, an inhibitor of caspase 8, prevented GCDC-induced cathepsin B activation and apoptosis. Consistent with these results, an increase in caspase 8-like activity was observed in GCDC-treated cells. Examination of the mechanism of GCDC-induced caspase 8 activation revealed that dominant-negative FADD inhibited apoptosis and that hepatocytes isolated from Fas-deficient lymphoproliferative mice were resistant to GCDC-induced apoptosis. After GCDC treatment, immunoprecipitation experiments demonstrated Fas oligomerization, and confocal microscopy demonstrated DeltaFADD-GFP (Fas-associated death domain-green fluorescent protein, aggregation in the absence of detectable Fas ligand mRNA. Collectively, these data suggest that GCDC-induced hepatocyte apoptosis involves ligand-independent oligomerization of Fas, recruitment of FADD, activation of caspase 8, and subsequent activation of effector proteases, including downstream caspases and cathepsin B.

Clinical utility of measuring infliximab and human anti-chimeric antibody concentrations in patients with inflammatory bowel disease.

OBJECTIVES:Human anti-chimeric antibodies (HACAs) and subtherapeutic infliximab concentrations are associated with decreased duration of response. We evaluated the clinical utility of measuring HACA and infliximab concentrations.METHODS:The medical records of patients with inflammatory bowel disease (IBD) who had HACA and infliximab concentrations measured were reviewed to determine whether the result affected clinical management.RESULTS:One hundred fifty-five patients had HACA and infliximab concentrations measured. The main indications for testing were loss of response to infliximab (49%), partial response after initiation of infliximab (22%), and possible autoimmune/delayed hypersensitivity reaction (10%). HACAs were identified in 35 patients (23%) and therapeutic infliximab concentrations in 51 patients (33%). Of 177 tests assessed, the results impacted treatment decisions in 73%. In HACA-positive patients, change to another anti-tumor necrosis factor (TNF) agent was associated with a complete or partial response in 92% of patients, whereas dose escalation had a response of 17%. In patients with subtherapeutic infliximab concentrations, dose escalation was associated with complete or partial clinical response in 86% of patients whereas changing to another anti-TNF agent had a response of 33%. Patients with clinical symptoms and therapeutic infliximab concentrations were continued at the same dose 76% of the time and had no evidence of active inflammation by endoscopic/radiographic assessment 62% of the time.CONCLUSIONS:Measurement of HACA and infliximab concentration impacts management and is clinically useful. Increasing the infliximab dose in patients who have HACAs is ineffective, whereas in patients with subtherapeutic infliximab concentrations, this strategy may be a good alternative to changing to another anti-TNF agent.

Circulating and gut-resident human Th17 cells express CD161 and promote intestinal inflammation

The C-type lectin-like receptor CD161, which has recently been described to promote T cell expansion, is expressed on a discrete subset of human CD4 T cells. The function of such cells, however, has remained elusive. We now demonstrate that CD161+ CD4 T cells comprise a circulating and gut-resident T helper 17 (Th17) cell population. During Crohns disease (CD), these CD161+ cells display an activated Th17 phenotype, as indicated by increased expression of interleukin (IL)-17, IL-22, and IL-23 receptor. CD161+ CD4 T cells from CD patients readily produce IL-17 and interferon γ upon stimulation with IL-23, whereas, in healthy subjects, priming by additional inflammatory stimuli such as IL-1β was required to enable IL-23–induced cytokine release. Circulating CD161+ Th17 cells are imprinted for gut homing, as indicated by high levels of CC chemokine receptor 6 and integrin β7 expression. Supporting their colitogenic phenotype, CD161+ Th17 cells were found in increased numbers in the inflammatory infiltrate of CD lesions and induced expression of inflammatory mediators by intestinal cells. Our data identify CD161+ CD4 T cells as a resting Th17 pool that can be activated by IL-23 and mediate destructive tissue inflammation.

Development of chronic colitis is dependent on the cytokine MIF

The cytokine macrophage-migration inhibitory factor (MIF) is secreted by a number of cell types upon induction by lipopolysaccharide (LPS). Because colitis is dependent on interplay between the mucosal immune system and intestinal bacteria, we investigated the role of MIF in experimental colitis. MIF-deficient mice failed to develop disease, but reconstitution of MIF-deficient mice with wild-type innate immune cells restored colitis. In addition, established colitis could be treated with anti-MIF immunoglobulins. Thus, murine colitis is dependent on continuous MIF production by the innate immune system. Because we found increased plasma MIF concentrations in patients with Crohns disease, these data suggested that MIF is a new target for intervention in Crohns disease.

Small-bowel imaging in Crohn's disease: a prospective, blinded, 4-way comparison trial

BACKGROUND With the introduction of new techniques to image the small bowel, there remains uncertainty about their role for diagnosing Crohns disease. OBJECTIVE To assess the sensitivity and specificity of capsule endoscopy (CE), CT enterography (CTE), ileocolonoscopy, and small-bowel follow-through (SBFT) in the diagnosis of small bowel Crohns disease. METHODS Prospective, blinded trial. SETTING Inflammatory bowel disease clinic at an academic medical center. PATIENTS Known or suspected Crohns disease. Exclusion criteria included known abdominal abscess and non-steroidal anti-inflammatory drug (NSAID) use. Partial small-bowel obstruction (PSBO) at CTE excluded patients from subsequent CE. INTERVENTIONS Patients underwent all 4 tests over a 4-day period. MAIN OUTCOME MEASUREMENTS Sensitivity, specificity, and accuracy of each test to detect active small-bowel Crohns disease. The criterion standard was a consensus diagnosis based upon clinical presentation and all 4 studies. RESULTS Forty-one CTE examinations were performed. Seven patients (17%) had an asymptomatic PSBO. Forty patients underwent colonoscopy, 38 had SBFT studies, and 28 had CE examinations. Small-bowel Crohns disease was active in 51%, absent in 42%, inactive in 5%, and suspicious in 2% of patients. The sensitivity of CE for detecting active small-bowel Crohns disease was 83%, not significantly higher than CTE (83%), ileocolonoscopy (74%), or SBFT (65%). However, the specificity of CE (53%) was significantly lower than the other tests (P < .05). One patient developed a transient PSBO due to CE, but no patients had retained capsules. LIMITATION Use of a consensus clinical diagnosis as the criterion standard-but this is how Crohns disease is diagnosed in practice. CONCLUSIONS The sensitivity of CE for active small-bowel Crohns disease was not significantly different from CTE, ileocolonoscopy, or SBFT. However, lower specificity and the need for preceding small-bowel radiography (due to the high frequency of asymptomatic PSBO) may limit the utility of CE as a first-line test for Crohns disease.

Cutting Edge: The Natural Ligand for Glucocorticoid-Induced TNF Receptor-Related Protein Abrogates Regulatory T Cell Suppression

CD4+25+ regulatory T (Treg) cells maintain immunological self-tolerance through mechanisms that are only in part understood. Previous studies suggest that the glucocorticoid-induced TNFR-related protein (GITR), which is preferentially expressed on the surface of Treg cells, potentially provides a signal that abrogates Treg suppression. In this study, we show that a soluble form of mouse GITR ligand (sGITR-L) induces GITR-dependent NF-κB activation and blocks in vitro suppression mediated by both resting and preactivated polyclonal and Ag-specific Treg cells. Since sGITR-L along with rIL-2 induces proliferation of CD4+25+ cells, it appears that sGITR-L can break the anergic state of Treg cells. Because sGITR-L also up-regulates IL-2 secretion by activated CD4+25 −T cells, these two sGITR-L induced signals synergize to interfere with suppressor activity by CD4+25+ Treg cells.

The Cell Surface Receptor SLAM Controls T Cell and Macrophage Functions

Signaling lymphocyte activation molecule (SLAM), a glycoprotein expressed on activated lymphocytes and antigen-presenting cells, has been shown to be a coregulator of antigen-driven T cell responses and is one of the two receptors for measles virus. Here we show that T cell receptor–induced interleukin (IL)-4 secretion by SLAM−/− CD4+ cells is down-regulated, whereas interferon γ production by CD4+ T cells is only slightly up-regulated. Although SLAM controls production of IL-12, tumor necrosis factor, and nitric oxide in response to lipopolysaccharide (LPS) by macrophages, SLAM does not regulate phagocytosis and responses to peptidoglycan or CpG. Thus, SLAM acts as a coreceptor that regulates signals transduced by the major LPS receptor Toll-like receptor 4 on the surface of mouse macrophages. A defective macrophage function resulted in an inability of SLAM−/− C57Bl/6 mice to remove the parasite Leishmania major. We conclude that the coreceptor SLAM plays a central role at the interface of acquired and innate immune responses.

Safety and Efficacy of Adalimumab for Moderate to Severe Crohn's Disease in Children

BACKGROUND & AIMS The IMAgINE 1 study (NCT00409682) evaluated the safety and efficacy of adalimumab double-blind maintenance dosing regimens following open-label induction for pediatric patients with moderate to severe Crohns disease (CD). METHODS We studied 192 patients with Pediatric Crohns Disease Activity Index (PCDAI) scores >30 for whom conventional treatment was unsuccessful. Patients received open-label induction therapy with subcutaneous adalimumab at weeks 0 and 2 (160 mg and 80 mg, or 80 mg and 40 mg, for body weight ≥40 kg or <40 kg). At week 4, 188 patients were assigned to groups based on achievement of clinical response (defined as decrease in PCDAI ≥15 points from baseline; 155/188 [82.4%]) and prior exposure to infliximab (82/188 [43.6%]). Groups were given double-blind maintenance therapy with adalimumab at high (40 mg or 20 mg for body weight ≥40 kg or <40 kg; n = 93) or low doses (20 mg or 10 mg for body weight ≥40 kg or <40 kg; n = 95) every other week for 48 weeks. Clinical remission (PCDAI ≤10) at week 26 (the primary end point) was compared between groups using the Cochran-Mantel-Haenszel test, adjusting for strata, with nonresponder imputation. Adverse events were monitored to evaluate safety. RESULTS A total of 152 of 188 patients (80.9%) completed all 26 weeks of the study. At week 26, 63 patients (33.5%) were in clinical remission, with no significant difference between high- and low-dose groups (36/93 [38.7%] vs 27/95 [28.4%]; P = .075). No new safety signals were detected. CONCLUSIONS Adalimumab induced and maintained clinical remission of children with CD, with a safety profile comparable to that of adult patients with CD. More children who received high compared with low dose were in remission at week 26, but the difference between dose groups was not statistically significant.

SLAM is a microbial sensor that regulates bacterial phagosome functions in macrophages

Phagocytosis is a pivotal process by which macrophages eliminate microorganisms after recognition by pathogen sensors. Here we unexpectedly found that the self ligand and cell surface receptor SLAM functioned not only as a costimulatory molecule but also as a microbial sensor that controlled the killing of Gram-negative bacteria by macrophages. SLAM regulated activity of the NADPH oxidase NOX2 complex and phagolysosomal maturation after entering the phagosome, following interaction with the bacterial outer membrane proteins OmpC and OmpF. SLAM recruited a complex containing the intracellular class III phosphatidylinositol kinase Vps34, its regulatory protein kinase Vps15 and the autophagy-associated molecule beclin-1 to the phagosome, which was responsible for inducing the accumulation of phosphatidylinositol-3-phosphate, a regulator of both NOX2 function and phagosomal or endosomal fusion. Thus, SLAM connects the Gram-negative bacterial phagosome to ubiquitous cellular machinery responsible for the control of bacterial killing.

Review article: biological activity markers in inflammatory bowel disease.

Traditionally, inflammatory bowel disease activity is assessed by clinical activity indices that measure clinical symptoms and endoscopic indices that measure endoscopic inflammation. Biological markers are a non‐invasive way of objectively measuring inflammation and can play an adjunctive or primary role in the assessment of disease activity.