Do mucosal T cells prevent intestinal inflammation?

The regulatory, inflammatory, and T cell programming roles of interleukin-2 (IL-2)

Signaling through IL-2 induces the activation of pathways that lead to the proliferation, survival and cytokine production of effector T cells. However, through negative feedback mechanisms, internalization of the IL-2 receptor, induction of activation-induced cell death, and the generation of regulatory T cells, IL-2 also promotes the suppression of inflammatory responses. In regulatory T cells, IL-2 signaling upregulates the expression of FoxP3. Regulatory T cell induction by TGF-beta also requires IL-2. Additionally, pro-inflammatory and pro-survival pathways involving PI3K upon IL-2 stimulation is inhibited by PTEN in regulatory T cells. Importantly, IL-2 signaling is key for the development, expansion and maintenance of regulatory T cells. However, gamma(c) cytokines can replace requirements for IL-2 in regulatory T cells, although not with the same efficacy. The dual roles of IL-2 in inflammation are demonstrated in that mice deficient in both FoxP3 and IL-2 display less severe symptoms compared to FoxP3 deficient mice. Finally, IL-2 not only plays a key role in the induction of effector T cells and regulatory T cells, it also inhibits IL-17 producing T cells. By understanding complex dynamics of IL-2 interactions in the inflammatory response, therapies may be developed or modified for regulating immune related diseases.

Focus on mechanisms of inflammation in inflammatory bowel disease sites of inhibition: current and future therapies

Anti-TNF antibodies were the first biologic agents registered to treat patients who have CD and, more recently, patients who have UC. The sequence of events underlying the inflammatory reaction in IBD is extremely complex, however, and involves both the innate and antigen-driven adaptive immune system. Novel therapies are directed at several key players of this cascade. Blockade of T-cell proliferation and activation and inhibition of T-cell cytokines has been most extensively targeted by clinical trials in humans. Inhibition of adhesion molecules and the use of selected growth factors seem to have therapeutic potential. Restoration of regulatory T-cell and dendritic-cell function is still waiting to be explored in clinical trials. Although an increasing number of biologic therapies for IBD are being developed, the discovery of the full spectrum of treatment modalities is only beginning. Often, however, the clinical efficacy of biologic agents is investigated, and for some molecules is established, before mechanisms of action are specifically explored. Eight years after the Food and Drug Administration approved infliximab for the treatment of luminal CD, it is not known how this anti-TNF antibody actually dampens inflammation in IBD. The advent of newer anti-TNF agents is only postponing the answer.

Clonal expansion of double-positive intraepithelial lymphocytes by MHC class I-related chain A expressed in mouse small intestinal epithelium

Expression of a distant homologue MHC class I molecule, MHC class I-related chain A (MICA), has been found to be stress inducible and limited to the intestinal epithelium. This nonclassical MHC molecule is associated with various carcinomas in humans. To understand the biological consequences of MICA expression in the gut, we generated transgenic (Tg) mice (T3(b)-MICA Tg) under the control of the T3(b) promoter. The T3(b)-MICA Tg mice expressed MICA selectively in the intestine and had an increased number of TCRalphabeta CD4CD8alphaalpha, double-positive (DP) intraepithelial lymphocytes (IELs) in the small bowel. These MICA-expanded DP IELs exhibited a bias to Vbeta8.2 and overlapped motifs of the complementarity-determining region 3 region among various Tg mice. Hence, the overexpression of MICA resulted in a clonal expansion of DP IELs. Studies in model of inflammatory bowel disease showed that transgenic MICA was able to attenuate the acute colitis induced by dextran sodium sulfate administration. Therefore, this unique in vivo model will enable investigation of possible influences of stress-inducible MICA on the gut immune surveillance.

Basic aspects and pharmacology of probiotics: an overview of pharmacokinetics, mechanisms of action and side-effects

Probiotics have been defined as non-pathogenic micro-organisms that, when ingested, exert a positive influence on host health or physiology. Their pharmacology is more complex than that of inert drugs but is now being studied in detail. Some strains have a high survival capacity until they reach the faeces, whereas others are rapidly killed by acid and bile (a characteristic that can be used for the delivery of active intracellular components). Potential translocation and permanent colonization are rare but possible events; and should come under closer scrutiny. Mechanisms of action can be direct or indirect through modifications of the endogenous flora or through immunomodulation. The active components are poorly known but include bacterial formylated peptides, peptidoglycan cell wall constituents and nucleotides. Although the safety of commercial probiotics is excellent, this aspect should be studied in more detail, especially in immunocompromised hosts.

A pilot study on the use of the humanized anti-interleukin-2 receptor antibody daclizumab in active ulcerative colitis

OBJECTIVES

Medical therapy of refractory ulcerative colitis (UC) is associated with long-term side effects of cyclosporine and steroids. Because cyclosporine acts by inhibiting interleukin-2 (IL-2) production, we studied the efficacy and safety of humanized anti-IL2 receptor (CD25) antibodies daclizumab for refractory UC in an open label pilot study.

METHODS

Ten patients with chronically active UC received daclizumab, 1 mg/kg i.v. twice with a 4-wk interval. Clinical, endoscopic, and histological evaluation was scored at regular intervals. CD25 immunohistochemistry was followed in mucosal biopsies. The primary study endpoint was clinical improvement at wk 8.

RESULTS

Nine of 10 patients completed the study. The median clinical activity score decreased from a median of 8 (95% CI = 7.2-9.2) at baseline to 3.5 (95% CI = 1.4-4.9) at wk 8 (p < 0.005). Endoscopic scores were significantly decreased at wk 8 (wk 0: 8, 95% CI = 6.3-8.5; wk 8: 5.0, 95% CI = 2.6-6.3; p < 0.01). Mucosal biopsies showed a significant decrease in CD25+ cells, and there was a trend toward lower histology scores at wk 8. Quality of life as assessed by the Inflammatory Bowel Disease Questionnaire increased after therapy (baseline: 131, 95% CI = 119-178; wk 8: 169; 95% CI = 124-216, p < 0.05). Nausea was most frequently reported as an adverse event, but always in patients that were concomitantly started on azathioprine.

CONCLUSIONS

The anti-IL-2R antibody daclizumab was safe and well tolerated in acute UC. Patients experienced clinical benefit along with signs of endoscopic improvement, but further controlled trials are needed to determine the therapeutic benefit of this compound.

The host-microbe interface within the gut

Colonization with bacteria is critical for the normal structural and functional development and optimal function of the mucosal immune system. Unrestrained mucosal immune activation in response to bacterial signals from the lumen is, however, a risk factor for inflammatory bowel disease. Therefore, mucosal immune responses to indigenous flora require precise control and an immunosensory capacity for distinguishing commensals from pathogens. The use of germ-free animal models with selective colonization strategies combined with modern molecular techniques promises to clarify the molecular signals responsible for host-flora interactions in health and disease. At least half of the resident flora cannot be cultured by conventional techniques but are identifiable by molecular methods. Collectively, the resident flora represent a virtual organ with a metabolic activity in excess of the liver and a microbiome in excess of the human genome. An improved understanding of this hidden organ holds secrets relevant to several infectious, inflammatory and neoplastic disease mechanisms.

Probiotics and inflammatory bowel disease: from fads and fantasy to facts and future

Probiotic therapy is attracting the renewed interest of clinicians and basic investigators from a variety of traditional research disciplines. While the theoretical rationale for modifying the commensal flora of the gastrointestinal tract in specific circumstances appears sound and requires scientific pursuit, the field of probiotics has been clouded by exaggerated claims from some quarters. In general, many of the claims for therapeutic efficacy have not been well substantiated, but the field is now poised for evaluation within the realm of evidence-based medicine. Alterations in commensal bacterial flora within the gastrointestinal tract are associated with susceptibility to pathogens such as Clostridium difficile and there is persuasive evidence that the normal flora may participate in the pathogenesis of inflammatory bowel disease and other chronic diseases in genetically susceptible individuals. This has prompted various strategies to fortify or otherwise modify the enteric flora by dietary supplements containing probiotic formulations. Detailed comparisons of probiotic performance amongst different bacterial strains have not been performed in vivo in man or under clinical trial conditions, and the level of scientific characterisation of individual organisms has been variable. In addition, it cannot be assumed that the same probiotic is equally suitable for all individuals. Moreover, the heterogeneity of clinical disorders such as Crohn's disease and ulcerative colitis implies that strain-specific properties may be required for subset-specific categories of patients. While cocktails of probiotics offer convenience, therapeutic progress may require clarification of the mechanism of probiotic action and may be delayed until individual bacterial components have been rigorously studied. More importantly, the full potential of therapeutic manipulation of the enteric flora with probiotics or other strategies may not be optimally realised until the composition and metabolic activities of the normal flora are better understood.

Expression of cyclooxygenase-2 in intestinal goblet cells of pre-diabetic NOD mice

Cyclooxygenase, the rate-limiting enzyme in prostaglandin synthesis, is expressed in constitutive (COX-1) and inducible (COX-2) isoforms. The COX-2 has been proposed to be involved in development of autoimmune type 1 diabetes (T1D). We examined COX-2 expression in the gut-associated lymphoid tissue (GALT), and found COX-2 was strongly expressed in goblet cells of non-obese diabetic (NOD) mice at the apical villi at the age of 2.5 weeks, clearly before the onset of insulitis, while the expression in the control BALB/c mice was weak or absent at all ages (P < 0.001). Lipopolysaccharide (LPS) given intraperitoneally slightly increased COX-2 expression in the goblet cells and epithelium of both NOD and BALB/c mice. High-resolution confocal microscopy showed that the surroundings of the goblet cells contained no COX-2, implying that the enzyme is synthesized by the goblet cells. The COX-2 is secreted from goblet cells into the intestinal lumen along with mucins. The COX-2 concentration in the goblet cell of BALB/c and especially of NOD mice was markedly higher than that in the intraepithelial lymphocytes or lamina propria macrophages. High mucin COX-2 from goblet cells may increase luminal prostaglandin synthesis, alter epithelial permeability, modulate intestinal immune responses and modify functional properties of the lymphocytes in the GALT, which all may be important for the initiation of the autoimmune phenomenon in the NOD mice.

Colitis-related public T cells are selected in the colonic lamina propria of IL-10-deficient mice

IL-10 is an important regulatory cytokine in the mucosal immune system, as supported by the fact that mice deficient in IL-10 spontaneously develop Crohn's disease-like colitis. An aberrant, Th1-driven CD4(+) T-cell response to enteric bacteria seems to be important in the pathogenesis of this murine colitis. However, no specific bacteria or bacterial products have been identified, and whether the colitis is mediated by the activation of CD4(+) T cells that recognize specific peptide-MHC complexes is controversial. In this study, we analyzed the TCR beta chain complementarity determining region 3 length spectratype of colonic CD4(+) T cells isolated from diseased IL-10-deficient mice by using the Immunoscope technique. Screening of the diseased interleukin-10-deficient mice resulted in a restricted clonotype in TCR V beta 13 and 14 subfamilies of colonic CD4(+) T cells. In contrast, a Gaussian distribution of clonotype of individual TCR V beta subsets was observed in CD4(+) T cells from the peripheral lymphoid tissues. Although individual variability in the disease-related response was also noted in other IL-10-deficient mice maintained in La Jolla and Osaka, perhaps because of different stages of the disease, genetic background, or the housing environment, colitis-related public clones seemed to be shared in all the diseased mice tested. To address whether public clones were involved, we determined the DNA sequence of the clones. Public motifs were shared in colonic CD4(+) T cells from different background interleukin-10-deficient mice with colitis. The frequently found motifs were SXDWG and SATGNYAEQ. These motifs were not seen in the peripheral lymphoid tissues of diseased mice as well as the colon of non-diseased mice. Thus, the common motif may be related to a public gut-derived antigen, which could be important for the development of pathogenic CD4(+) T cells in this inflammatory bowel disease (IBD) model. The selection of V beta-J beta usage is perhaps stochastic in individual mice; however, the epigenetic generation of SXDWG motif by the recombination machinery and selection for this motif in the gut environment could be important for triggering IBD.

Inflammatory bowel disease: is the intestine a Trojan horse?

Inflammatory bowel disease (IBD) is a chronic relapsing inflammatory condition of the intestines that is clinically heterogenous. The cause(s) of IBD are currently unknown but the mechanisms of injury are immunological. Increasingly there is an emphasis on the study of the complex interactions at the interface of self and non-self--the gastrointestinal epithelial surface--in relationship to the pathogenesis of disease. There is mounting evidence that a lack of tolerance to the normal commensal flora of the intestine may underlie the disease pathogenesis. Several genetic loci that are markers of disease susceptibility have been identified. These loci map to areas of the genome that are concerned with antigen presentation or cytokine secretion and suggest a genetic heterogeneity that underlies the clinical differences. Overall a picture is emerging of defects in epithelial barrier function and, or immunoregulation leading to immune responses that are triggered or exaggerated by the antigenic components of the normal flora.

Constitutive expression of LIGHT on T cells leads to lymphocyte activation, inflammation, and tissue destruction

LIGHT, a member of the TNF family of cytokines (homologous to lymphotoxin, exhibits inducible expression and competes with HSV glycoprotein D for herpesvirus entry mediator, a receptor expressed on T cells), is induced on activated T cells and mediates costimulatory and antitumor activity in vitro. Relatively little information is available on the in vivo effects of LIGHT expression, particularly within the T cell compartment. In this work, we describe transgenic mice that express human LIGHT under the control of the CD2 promoter, resulting in constitutive transgene expression in cells of the T lymphocyte lineage. LIGHT-transgenic animals exhibit abnormalities in both lymphoid tissue architecture and the distribution of lymphocyte subsets. They also show signs of inflammation that are most severe in the intestine, along with tissue destruction of the reproductive organs. These LIGHT-mediated effects were recapitulated when immune-deficient mice were reconstituted with bone marrow from LIGHT-transgenic donor mice. T cells in the LIGHT-transgenic mice have an activated phenotype and mucosal T cells exhibit enhanced Th1 cytokine activity. The results indicate that LIGHT may function as an important regulator of T cell activation, and implicate LIGHT signaling pathways in inflammation focused on mucosal tissues.