Gavin W. Sewell

Disordered macrophage cytokine secretion underlies impaired acute inflammation and bacterial clearance in Crohn's disease

The cause of Crohns disease (CD) remains poorly understood. Counterintuitively, these patients possess an impaired acute inflammatory response, which could result in delayed clearance of bacteria penetrating the lining of the bowel and predispose to granuloma formation and chronicity. We tested this hypothesis in human subjects by monitoring responses to killed Escherichia coli injected subcutaneously into the forearm. Accumulation of 111In-labeled neutrophils at these sites and clearance of 32P-labeled bacteria from them were markedly impaired in CD. Locally increased blood flow and bacterial clearance were dependent on the numbers of bacteria injected. Secretion of proinflammatory cytokines by CD macrophages was grossly impaired in response to E. coli or specific Toll-like receptor agonists. Despite normal levels and stability of cytokine messenger RNA, intracellular levels of tumor necrosis factor (TNF) were abnormally low in CD macrophages. Coupled with reduced secretion, these findings indicate accelerated intracellular breakdown. Differential transcription profiles identified disease-specific genes, notably including those encoding proteins involved in vesicle trafficking. Intracellular destruction of TNF was decreased by inhibitors of lysosomal function. Together, our findings suggest that in CD macrophages, an abnormal proportion of cytokines are routed to lysosomes and degraded rather than being released through the normal secretory pathway.

Immunosuppression in acutely decompensated cirrhosis is mediated by prostaglandin E2.

Liver disease is one of the leading causes of death worldwide. Patients with cirrhosis display an increased predisposition to and mortality from infection due to multimodal defects in the innate immune system; however, the causative mechanism has remained elusive. We present evidence that the cyclooxygenase (COX)-derived eicosanoid prostaglandin E2 (PGE2) drives cirrhosis-associated immunosuppression. We observed elevated circulating concentrations (more than seven times as high as in healthy volunteers) of PGE2 in patients with acute decompensation of cirrhosis. Plasma from these and patients with end-stage liver disease (ESLD) suppressed macrophage proinflammatory cytokine secretion and bacterial killing in vitro in a PGE2-dependent manner via the prostanoid type E receptor-2 (EP2), effects not seen with plasma from patients with stable cirrhosis (Child-Pugh score grade A). Albumin, which reduces PGE2 bioavailability, was decreased in the serum of patients with acute decompensation or ESLD (<30 mg/dl) and appears to have a role in modulating PGE2-mediated immune dysfunction. In vivo administration of human albumin solution to these patients significantly improved the plasma-induced impairment of macrophage proinflammatory cytokine production in vitro. Two mouse models of liver injury (bile duct ligation and carbon tetrachloride) also exhibited elevated PGE2, reduced circulating albumin concentrations and EP2-mediated immunosuppression. Treatment with COX inhibitors or albumin restored immune competence and survival following infection with group B Streptococcus. Taken together, human albumin solution infusions may be used to reduce circulating PGE2 levels, attenuating immune suppression and reducing the risk of infection in patients with acutely decompensated cirrhosis or ESLD.

Crohn's disease: an immune deficiency state.

Crohn’s disease is a chronic inflammatory disorder primarily affecting the gastrointestinal tract. Its clinical manifestations arise from a substantial infiltration of the intestinal mucosa by activated leukocytes and the downstream consequences of chronic inflammation. The underlying cause driving this immunological reaction remains poorly understood. A number of hypotheses have been proposed, most of which postulate a primary over-activation of the immune response, based on the pathological appearances of active Crohn’s lesions. Interestingly, none of these theories have been mechanistically proven. It is possible that the immunological events responsible for disease initiation are quite different from those contributing to its persistence and propagation. A substantial body of data has emerged in recent years to suggest that the primary defect in Crohn’s disease is actually one of relative immunodeficiency. This review considers the evidence for such a phenomenon in contrast to alternative prevailing hypotheses and attempts to address some of the potential paradoxes that it generates.

Disruption of macrophage pro-inflammatory cytokine release in Crohn's disease is associated with reduced optineurin expression in a subset of patients

Crohns disease (CD) is a complex and highly heterogeneous chronic inflammatory disorder, primarily affecting the gastrointestinal tract. Genetic and functional studies have highlighted a key role for innate immunity in its pathogenesis. Profound systemic defects in innate immunity and acute inflammation are understood to result in markedly delayed clearance of bacteria from the tissues, leading to local chronic granulomatous inflammation and compensatory adaptive immunological changes. Macrophages, key orchestrators of acute inflammation, are likely to play an important role in the initial impaired innate immune response. Monocyte‐derived macrophages from CD patients stimulated with Escherichia coli were shown to release attenuated levels of tumour necrosis factor and interferon‐γ with normal secretion of interleukin‐8 (IL‐8), IL‐10 and IL‐6. In controls, the secretion of these cytokines was strongly positively correlated, which was not seen with CD macrophages. The transcriptomes of CD and control macrophages were examined in an attempt to understand the molecular basis of this defect. There were no differentially expressed genes identified between the two groups, consistent with genetic heterogeneity; however, a number of molecules were found to be under‐expressed in subgroups of CD patients. The most common of these was optineurin (OPTN) which was under‐expressed in approximately 10% of the CD patients. Reduced OPTN expression coincided with lower intracellular protein levels and diminished cytokine secretion after bacterial stimulation both in the patients and with small interfering RNA knockdown in THP‐1 cells. Identifying and studying subgroups of patients with shared defective gene expression could aid our understanding of the mechanisms underlying highly heterogeneous diseases such as CD.

Defective tumor necrosis factor release from Crohn's disease macrophages in response to Toll-like receptor activation: relationship to phenotype and genome-wide association susceptibility loci.

Background: Recent work provides evidence of a failure of acute inflammation in Crohns disease (CD), and suggests that the primary defect operates at the level of the macrophage and cytokine release. Here we extend the characterization of the innate immune defect in CD by investigating the macrophage response to Toll‐like receptor (TLR) agonists and assess potential links between genome‐wide association study (GWAS) susceptibility loci, disease phenotype, and therapeutic regimens on tumor necrosis factor &agr; (TNF) release. Methods: Peripheral blood‐derived macrophages were cultured from control subjects and patients with CD, stimulated with TLR ligands, and the release of TNF measured. Genomic DNA was purified from blood and genotyped for 34 single nucleotide polymorphisms (SNPs) identified as being associated with CD by GWAS. Results: All stimuli resulted in a reduction (32%–48%) in TNF release from macrophages derived from CD patients (n = 28–101) compared to those from healthy control (HC) subjects. All phenotypes demonstrated impaired TNF release, with the greatest defect in patients with colonic disease. There was no detectable relationship between the level of TNF released and the presence of GWAS susceptibility loci in CD patients. Reduced TNF levels were not influenced by age, gender, or use of aminosalicylate (5‐ASA) medication. Conclusions: This study supports the hypothesis of defective proinflammatory cytokine secretion and an innate immunodeficiency in CD. Abnormal TNF secretion is evident downstream of multiple TLRs, affects all disease phenotypes, and is unrelated to 34 polymorphisms associated with CD by GWAS. (Inflamm Bowel Dis 2012;)

Diminished Macrophage Apoptosis and Reactive Oxygen Species Generation after Phorbol Ester Stimulation in Crohn's Disease

Background Crohns Disease (CD) is a chronic relapsing disorder characterized by granulomatous inflammation of the gastrointestinal tract. Although its pathogenesis is complex, we have recently shown that CD patients have a systemic defect in macrophage function, which results in the defective clearance of bacteria from inflammatory sites. Methodology/Principal Findings Here we have identified a number of additional macrophage defects in CD following diacylglycerol (DAG) homolog phorbol-12-myristate-13-acetate (PMA) activation. We provide evidence for decreased DNA fragmentation, reduced mitochondrial membrane depolarization, impaired reactive oxygen species production, diminished cytochrome c release and increased IL-6 production compared to healthy subjects after PMA exposure. The observed macrophage defects in CD were stimulus-specific, as normal responses were observed following p53 activation and endoplasmic reticulum stress. Conclusion These findings add to a growing body of evidence highlighting disordered macrophage function in CD and, given their pivotal role in orchestrating inflammatory responses, defective apoptosis could potentially contribute to the pathogenesis of CD.

Lipidomic profiling in Crohn's disease: Abnormalities in phosphatidylinositols, with preservation of ceramide, phosphatidylcholine and phosphatidylserine composition

Crohns disease is a chronic inflammatory condition largely affecting the terminal ileum and large bowel. A contributing cause is the failure of an adequate acute inflammatory response as a result of impaired secretion of pro-inflammatory cytokines by macrophages. This defective secretion arises from aberrant vesicle trafficking, misdirecting the cytokines to lysosomal degradation. Aberrant intestinal permeability is also well-established in Crohns disease. Both the disordered vesicle trafficking and increased bowel permeability could result from abnormal lipid composition. We thus measured the sphingo- and phospholipid composition of macrophages, using mass spectrometry and stable isotope labelling approaches. Stimulation of macrophages with heat-killed Escherichia coli resulted in three main changes; a significant reduction in the amount of individual ceramide species, an altered composition of phosphatidylcholine, and an increased rate of phosphatidylcholine synthesis in macrophages. These changes were observed in macrophages from both healthy control individuals and patients with Crohns disease. The only difference detected between control and Crohns disease macrophages was a reduced proportion of newly-synthesised phosphatidylinositol 16:0/18:1 over a defined time period. Shotgun lipidomics analysis of macroscopically non-inflamed ileal biopsies showed a significant decrease in this same lipid species with overall preservation of sphingolipid, phospholipid and cholesterol composition.

Optineurin deficiency in mice contributes to impaired cytokine secretion and neutrophil recruitment in bacteria-driven colitis

ABSTRACT Crohns disease (CD) is associated with delayed neutrophil recruitment and bacterial clearance at sites of acute inflammation as a result of impaired secretion of proinflammatory cytokines by macrophages. To investigate the impaired cytokine secretion and confirm our previous findings, we performed transcriptomic analysis in macrophages and identified a subgroup of individuals with CD who had low expression of the autophagy receptor optineurin (OPTN). We then clarified the role of OPTN deficiency in: macrophage cytokine secretion; mouse models of bacteria-driven colitis and peritonitis; and zebrafish Salmonella infection. OPTN-deficient bone-marrow-derived macrophages (BMDMs) stimulated with heat-killed Escherichia coli secreted less proinflammatory TNFα and IL6 cytokines despite similar gene transcription, which normalised with lysosomal and autophagy inhibitors, suggesting that TNFα is mis-trafficked to lysosomes via bafilomycin-A-dependent pathways in the absence of OPTN. OPTN-deficient mice were more susceptible to Citrobacter colitis and E. coli peritonitis, and showed reduced levels of proinflammatory TNFα in serum, diminished neutrophil recruitment to sites of acute inflammation and greater mortality, compared with wild-type mice. Optn-knockdown zebrafish infected with Salmonella also had higher mortality. OPTN plays a role in acute inflammation and neutrophil recruitment, potentially via defective macrophage proinflammatory cytokine secretion, which suggests that diminished OPTN expression in humans might increase the risk of developing CD. Summary: Optineurin plays a role in acute inflammation, proinflammatory cytokine secretion and neutrophil recruitment, which suggests that diminished optineurin expression in humans might increase the risk of developing Crohns disease.

Crohn’s disease as an immunodeficiency

The pathogenesis of Crohn’s disease (CD) has widely been regarded as the consequence of a dysregulated T-cell-mediated response to intestinal microbes, and the majority of the worldwide research effort has focused on characterizing and treating the chronic inflammatory phase of the disease. However, recent molecular biological and clinical investigations indicate that CD is actually a primary immunodeficiency. At first counter-intuitive, the apparent paradox of a pathogenic innate immune defect can be linked mechanistically to the granulomatous chronic inflammation characteristic of the disease. Genome-wide association studies have corroborated the involvement of innate immune dysfunction in the pathogenesis of CD, but less than 20% of the heritable risk is accounted for. By contrast, in vitro and in vivo stimulation of the immune system has highlighted novel areas of interest that may lead to the development of targeted therapeutic and diagnostic tools.

Mucosal Transcriptomics Implicates Under Expression of BRINP3 in the Pathogenesis of Ulcerative Colitis

Background:Mucosal abnormalities are potentially important in the primary pathogenesis of ulcerative colitis (UC). We investigated the mucosal transcriptomic expression profiles of biopsies from patients with UC and healthy controls, taken from macroscopically noninflamed tissue from the terminal ileum and 3 colonic locations with the objective of identifying abnormal molecules that might be involved in disease development. Methods:Whole-genome transcriptional analysis was performed on intestinal biopsies taken from 24 patients with UC, 26 healthy controls, and 14 patients with Crohns disease. Differential gene expression analysis was performed at each tissue location separately, and results were then meta-analyzed. Significantly, differentially expressed genes were validated using quantitative polymerase chain reaction. The location of gene expression within the colon was determined using immunohistochemistry, subcellular fractionation, electron and confocal microscopy. DNA methylation was quantified by pyrosequencing. Results:Only 4 probes were abnormally expressed throughout the colon in patients with UC with Bone morphogenetic protein/Retinoic acid Inducible Neural-specific 3 (BRINP3) being the most significantly underexpressed. Attenuated expression of BRINP3 in UC was independent of current inflammation, unrelated to phenotype or treatment, and remained low at rebiopsy an average of 22 months later. BRINP3 is localized to the brush border of the colonic epithelium and expression is influenced by DNA methylation within its promoter. Conclusions:Genome-wide expression analysis of noninflamed mucosal biopsies from patients with UC identified BRINP3 as significantly underexpressed throughout the colon in a large subset of patients with UC. Low levels of this gene could predispose or contribute to the maintenance of the characteristic mucosal inflammation seen in this condition.