Peter J. Mannon

The fundamental basis of inflammatory bowel disease

Two broad hypotheses have arisen regarding the fundamental nature of the pathogenesis of inflammatory bowel diseases (IBDs, which include ulcerative colitis and Crohn disease). The first contends that primary dysregulation of the mucosal immune system leads to excessive immunologic responses to normal microflora. The second suggests that changes in the composition of gut microflora and/or deranged epithelial barrier function elicits pathologic responses from the normal mucosal immune system. Here we examine these hypotheses and conclude that IBD is indeed characterized by an abnormal mucosal immune response but that microbial factors and epithelial cell abnormalities can facilitate this response.

Nonclassical CD1d-restricted NK T cells that produce IL-13 characterize an atypical Th2 response in ulcerative colitis

While Crohn disease (CD) has been clearly identified as a Th1 inflammation, the immunopathogenesis of its counterpart inflammatory bowel disease, ulcerative colitis (UC), remains enigmatic. Here we show that lamina propria T (LPT) cells from UC patients produce significantly greater amounts of IL-13 (and IL-5) than control cells and little IFN-gamma, whereas comparable cells from CD patients produce large amounts of IFN-gamma and small amounts of IL-13. We then show that stimulation of UC LPT cells bearing an NK marker (CD161) with anti-CD2/anti-CD28 or with B cells expressing transfected CD1d induces substantial IL-13 production. While this provided firm evidence that the IL-13-producing cell is an NK T (NKT) cell, it became clear that this cell does not express invariant NKT cell receptors characteristic of most NKT cells since there was no increase in cells binding alpha-galactosylceramide-loaded tetramers, and alpha-galactosylceramide did not induce IL-13 secretion. Finally, we show that both human NKT cell lines as well as UC CD161(+) LPT cells are cytotoxic for HT-29 epithelial cells and that this cytotoxicity is augmented by IL-13. These studies show that UC is associated with an atypical Th2 response mediated by nonclassical NKT cells producing IL-13 and having cytotoxic potential for epithelial cells.

Persistence of HIV in Gut-Associated Lymphoid Tissue despite Long-Term Antiretroviral Therapy

Human immunodeficiency virus (HIV) persists in peripheral blood mononuclear cells despite sustained, undetectable plasma viremia resulting from long-term antiretroviral therapy. However, the source of persistent HIV in such infected individuals remains unclear. Given recent data suggesting high levels of viral replication and profound depletion of CD4(+) T cells in gut-associated lymphoid tissue (GALT) of animals infected with simian immunodeficiency virus and HIV-infected humans, we sought to determine the level of CD4(+) T cell depletion as well as the degree and extent of HIV persistence in the GALT of infected individuals who had been receiving effective antiviral therapy for prolonged periods of time. We demonstrate incomplete recoveries of CD4(+) T cells in the GALT of aviremic, HIV-infected individuals who had received up to 9.9 years of effective antiretroviral therapy. In addition, we demonstrate higher frequencies of HIV infection in GALT, compared with PBMCs, in these aviremic individuals and provide evidence for cross-infection between these 2 cellular compartments. Together, these data provide a possible mechanism for the maintenance of viral reservoirs revolving around the GALT of HIV-infected individuals despite long-term viral suppression and suggest that the GALT may play a major role in the persistence of HIV in such individuals.

Composition of the adult digestive tract bacterial microbiome based on seven mouth surfaces, tonsils, throat and stool samples

BackgroundTo understand the relationship between our bacterial microbiome and health, it is essential to define the microbiome in the absence of disease. The digestive tract includes diverse habitats and hosts the human bodys greatest bacterial density. We describe the bacterial community composition of ten digestive tract sites from more than 200 normal adults enrolled in the Human Microbiome Project, and metagenomically determined metabolic potentials of four representative sites.ResultsThe microbiota of these diverse habitats formed four groups based on similar community compositions: buccal mucosa, keratinized gingiva, hard palate; saliva, tongue, tonsils, throat; sub- and supra-gingival plaques; and stool. Phyla initially identified from environmental samples were detected throughout this population, primarily TM7, SR1, and Synergistetes. Genera with pathogenic members were well-represented among this disease-free cohort. Tooth-associated communities were distinct, but not entirely dissimilar, from other oral surfaces. The Porphyromonadaceae, Veillonellaceae and Lachnospiraceae families were common to all sites, but the distributions of their genera varied significantly. Most metabolic processes were distributed widely throughout the digestive tract microbiota, with variations in metagenomic abundance between body habitats. These included shifts in sugar transporter types between the supragingival plaque, other oral surfaces, and stool; hydrogen and hydrogen sulfide production were also differentially distributed.ConclusionsThe microbiomes of ten digestive tract sites separated into four types based on composition. A core set of metabolic pathways was present across these diverse digestive tract habitats. These data provide a critical baseline for future studies investigating local and systemic diseases affecting human health.

Both IL-12p70 and IL-23 Are Synthesized During Active Crohn's Disease and Are Down-regulated by Treatment with Anti-IL-12 p40 Monoclonal Antibody

Background: Interleukin (IL)‐12p70 and IL‐23 are key T helper‐1 (TH1) cytokines that drive the inflammation seen in numerous models of intestinal inflammation. These molecules contain an identical p40 chain that is bound to a p35 chain in IL‐12 and a p19 chain in IL‐23, making both potentially susceptible to modulation by an anti‐IL‐12p40 monoclonal antibody (mAb). Methods: In the present study, we sought to determine whether active inflammation in Crohns disease (CD) is associated with the increased synthesis of both of these cytokines and whether patients treated with an anti‐IL‐12p40 mAb down‐regulate IL‐23 as well as IL‐12p70 as previous reported. Results: To this end we initially determined that IL‐12p70 secretion by control and CD antigen‐presenting cells (macrophages) in lamina propria mononuclear populations is optimized by stimulation with CD40L and interferon‐&ggr;. In subsequent studies using these stimulation conditions we found that patients with CD manifested both increased IL‐12p70 and IL‐23 secretion before anti‐IL‐12p40 mAb treatment and normal levels of secretion of these cytokines following cessation of treatment. Antigen‐presenting cells in lamina propria mononuclear cells from ulcerative colitis patients, in contrast, produced only baseline levels of IL‐23. Finally, we found that IL‐23‐induced T cell production of IL‐17 and IL‐6 are also greatly reduced after antibody treatment. The latter data are parallel to those from previous studies showing that anti‐IL‐12p40 down‐regulates IFN‐&ggr; and tumor necrosis factor‐&agr; secretion. Conclusions: We conclude that CD but not ulcerative colitis is associated with high levels of both IL‐12p70 and IL‐23 secretion as well as the secretion of downstream effector cytokines, and that this cytokine production is down‐regulated following administration of IL‐12p40 mAb.

Coagulation defects and altered hemodynamic responses in mice lacking receptors for thromboxane A2.

Thromboxane A2 (TXA2) is a labile metabolite of arachidonic acid that has potent biological effects. Its actions are mediated by G protein-coupled thromboxane-prostanoid (TP) receptors. TP receptors have been implicated in the pathogenesis of cardiovascular diseases. To investigate the physiological functions of TP receptors, we generated TP receptor-deficient mice by gene targeting. Tp-/- animals reproduce and survive in expected numbers, and their major organ systems are normal. Thromboxane agonist binding cannot be detected in tissues from Tp-/- mice. Bleeding times are prolonged in Tp-/- mice and their platelets do not aggregate after exposure to TXA2 agonists. Aggregation responses after collagen stimulation are also delayed, although ADP-stimulated aggregation is normal. Infusion of the TP receptor agonist U-46619 causes transient increases in blood pressure followed by cardiovascular collapse in wild-type mice, but U-46619 caused no hemodynamic effect in Tp-/- mice. Tp-/- mice are also resistant to arachidonic acid-induced shock, although arachidonic acid signifi-cantly reduced blood pressure in Tp-/- mice. In summary, Tp-/- mice have a mild bleeding disorder and altered vascular responses to TXA2 and arachidonic acid. Our studies suggest that most of the recognized functions of TXA2 are mediated by the single known Tp gene locus.

Angiotensin II regulates cellular immune responses through a calcineurin-dependent pathway

The renin-angiotensin system (RAS) is a key regulator of vascular tone and blood pressure. In addition, angiotensin II also has a number of cellular effects that may contribute to disease pathogenesis. Using Agtr1a(-/-) mice, which lack AT(1A) receptors for angiotensin II, we have identified a novel function of the RAS to modulate the immune system. We find that angiotensin II, acting through type 1 (AT(1)) receptors on immune cells, triggers the proliferation of splenic lymphocytes. These actions contribute to the vigor of cellular alloimmune responses. Within lymphoid organs, sufficient components of the RAS are present to activate AT(1) receptors during an immune response, promoting cell growth. These actions require activation of calcineurin phosphatase. In an in vivo model of cardiac transplantation, the absence of AT(1) signaling accentuates the immunosuppressive effects of the calcineurin inhibitor cyclosporine. We conclude that inhibition of AT(1) receptor signaling should be useful as an anti-inflammatory and immunosuppressive therapy. Furthermore, the actions of the RAS to promote lymphocyte activation may contribute to inflammation that characterizes a number of diseases of the heart and the vascular system.

Suppression of inflammation in ulcerative colitis by interferon-β-1a is accompanied by inhibition of IL-13 production

Objective Ulcerative colitis is associated with increased interleukin 13 (IL-13) production by natural killer T cells. Taking advantage of the inhibitory actions of interferon β on IL-13 expression, this proof-of-concept study aimed to show that decreasing IL-13 production is associated with clinical improvement of ulcerative colitis symptoms. Design Open-label interventional drug trial. Setting Outpatient clinical research hospital. Patients Adult patients with active ulcerative colitis (Short Clinical Colitis Activity Index (SCCAI)≥5). Interventions Treatment with 30 μg IM interferon-β-1a (Avonex) weekly for 12 weeks with 6 month follow-up. Main outcome measures Clinical response was defined as ≥3 point drop in the SCCAI for at least two consecutive monitoring visits, and cytokine production was measured in cultured peripheral blood and lamina propria mononuclear cells (LPMC) before and after treatment. Results 11 of 16 patients were clinical responders, and 4 were in remission (SCCAI ≤ 2) at the end of treatment. Rectal bleeding subscores improved dramatically by week 4 (38% with frank bleeding vs 87% pretreatment). Increased IL-13 production by LPMC T cells fell significantly in clinical responders (690±99 vs 297±58 pg/ml p=0.015) but was unchanged in non-responders (542±83 vs 510±39 pg/ml). In addition, non-responders had significantly higher production of IL-17 and IL-6 pre-treatment compared to responders. Conclusions Interferon-β-1a induces clinical response and remission in a large subset of patients with ulcerative colitis that is associated with significant inhibition of IL-13 production. In addition, increased IL-17 and IL-6 production is associated with no response to interferon-β. These data provide a proof-of-concept that IL-13 is an effector cytokine in ulcerative colitis and should be a target for novel therapies.

Cycling of Gut Mucosal CD4+ T Cells Decreases after Prolonged Anti-Retroviral Therapy and is Associated with Plasma LPS Levels

The gut mucosa is an important site of HIV immunopathogenesis with severe depletion of CD4+ T cells occurring during acute infection. The effect of prolonged anti-retroviral therapy (ART) on cycling and restoration of T lymphocytes in the gut remains unclear. Colon and terminal ileal biopsies and peripheral blood samples were collected from viremic, untreated, HIV-infected participants, patients treated with prolonged ART (>5 years), and uninfected controls and analyzed by flow cytometry. In the gut, the proportion of cycling T cells decreased and the number of CD4+ T cells normalized in treated patients in parallel with β7 expression on CD4+ T cells in blood. Cycling of gut T cells in viremic patients was associated with increased plasma LPS levels, but not colonic HIV–RNA. These data suggest that gut T-cell activation and microbial translocation may be interconnected whereas prolonged ART may decrease activation and restore gut CD4+ T cells.

Interleukin 13 and its role in gut defence and inflammation

Interleukin 13 (IL-13) is a cytokine of increasing interest to gastroenterologists because of its developing role in ulcerative colitis, eosinophilic oesophagitis (EO) and fibrosis. Recent data show that IL-13 may play an important role in a novel innate immune response since it can be released by signals from an injured or inflamed epithelium, of particular relevance to the gut. Animal models of IL-13-driven inflammation (from asthma to colitis and EO) are being translated to human disease and providing insight into potential strategies for new therapies. In fact, multiple clinical trials using anti-IL-13 drugs are underway in asthma and are being extended to gastrointestinal diseases. This review presents the current knowledge on IL-13 production and function in the gut, including the cells and receptor signalling pathways involved in mediating IL-13 effects, the proposed mechanisms of IL-13 induced gut disease and the many drugs currently being tested that target IL-13 related pathways.