Holm H. Uhlig

Cutting Edge: Cure of Colitis by CD4+CD25+ Regulatory T Cells

CD4+CD25+ regulatory T cells have been shown to prevent T cell-mediated immune pathology; however, their ability to ameliorate established inflammation has not been tested. Using the CD4+CD45RBhigh T cell transfer model of inflammatory bowel disease, we show that CD4+CD25+ but not CD4+CD25−CD45RBlow T cells are able to cure intestinal inflammation. Transfer of CD4+CD25+ T cells into mice with colitis led to resolution of the lamina propria infiltrate in the intestine and reappearance of normal intestinal architecture. CD4+CD25+ T cells were found to proliferate in the mesenteric lymph nodes and inflamed colon. They were located between clusters of CD11c+ cells and pathogenic T cells and found to be in contact with both cell types. These studies suggest that manipulation of CD4+CD25+ T cells may be beneficial in the treatment of chronic inflammatory diseases.

Innate lymphoid cells drive interleukin-23-dependent innate intestinal pathology.

The key role of interleukin (IL)-23 in the pathogenesis of autoimmune and chronic inflammatory disorders is supported by the identification of IL-23 receptor (IL-23R) susceptibility alleles associated with inflammatory bowel disease, psoriasis and ankylosing spondylitis. IL-23-driven inflammation has primarily been linked to the actions of T-helper type 17 (TH17) cells. Somewhat overlooked, IL-23 also has inflammatory effects on innate immune cells and can drive T-cell-independent colitis. However, the downstream cellular and molecular pathways involved in this innate intestinal inflammatory response are poorly characterized. Here we show that bacteria-driven innate colitis is associated with an increased production of IL-17 and interferon-γ in the colon. Stimulation of colonic leukocytes with IL-23 induced the production of IL-17 and interferon-γ exclusively by innate lymphoid cells expressing Thy1, stem cell antigen 1 (SCA-1), retinoic-acid-related orphan receptor (ROR)-γt and IL-23R, and these cells markedly accumulated in the inflamed colon. IL-23-responsive innate intestinal cells are also a feature of T-cell-dependent models of colitis. The transcription factor ROR-γt, which controls IL-23R expression, has a functional role, because Rag-/-Rorc-/- mice failed to develop innate colitis. Last, depletion of Thy1+ innate lymphoid cells completely abrogated acute and chronic innate colitis. These results identify a previously unrecognized IL-23-responsive innate lymphoid population that mediates intestinal immune pathology and may therefore represent a target in inflammatory bowel disease.

Essential role for CD103 in the T cell–mediated regulation of experimental colitis

The integrin CD103 is highly expressed at mucosal sites, but its role in mucosal immune regulation remains poorly understood. We have analyzed the functional role of CD103 in intestinal immune regulation using the T cell transfer model of colitis. Our results show no mandatory role for CD103 expression on T cells for either the development or CD4+CD25+ regulatory T (T reg) cell–mediated control of colitis. However, wild-type CD4+CD25+ T cells were unable to prevent colitis in immune-deficient recipients lacking CD103, demonstrating a nonredundant functional role for CD103 on host cells in T reg cell–mediated intestinal immune regulation. Non–T cell expression of CD103 is restricted primarily to CD11chighMHC class IIhigh dendritic cells (DCs). This DC population is present at a high frequency in the gut-associated lymphoid tissue and appears to mediate a distinct functional role. Thus, CD103+ DCs, but not their CD103− counterparts, promoted expression of the gut-homing receptor CCR9 on T cells. Conversely, CD103− DCs promoted the differentiation of IFN-γ–producing T cells. Collectively, these data suggest that CD103+ and CD103− DCs represent functionally distinct subsets and that CD103 expression on DCs influences the balance between effector and regulatory T cell activity in the intestine.

Characterization of Foxp3+CD4+CD25+ and IL-10-Secreting CD4+CD25+ T Cells during Cure of Colitis

CD4+CD25+ regulatory T cells can prevent and resolve intestinal inflammation in the murine T cell transfer model of colitis. Using Foxp3 as a marker of regulatory T cell activity, we now provide a comprehensive analysis of the in vivo distribution of Foxp3+CD4+CD25+ cells in wild-type mice, and during cure of experimental colitis. In both cases, Foxp3+CD4+CD25+ cells were found to accumulate in the colon and secondary lymphoid organs. Importantly, Foxp3+ cells were present at increased density in colon samples from patients with ulcerative colitis or Crohn’s disease, suggesting similarities in the behavior of murine and human regulatory cells under inflammatory conditions. Cure of murine colitis was dependent on the presence of IL-10, and IL-10-producing CD4+CD25+ T cells were enriched within the colon during cure of colitis and also under steady state conditions. Our data indicate that although CD4+CD25+ T cells expressing Foxp3 are present within both lymphoid organs and the colon, subsets of IL-10-producing CD4+CD25+ T cells are present mainly within the intestinal lamina propria suggesting compartmentalization of the regulatory T cell response at effector sites.

Regulatory T cells and intestinal homeostasis

Summary:  Murine models of inflammatory bowel disease (IBD) are useful tools for the study of the pathogenesis and regulation of intestinal inflammation. Colitis can be induced in immune‐deficient mice following transfer of populations of T cells or following infection with Helicobacter hepaticus and other intestinal pathogens. In these situations, colitis occurs as a result of the absence of a specialized population of regulatory cells, as transfer of CD4+CD25+ T cells prevents disease. Importantly, from a clinical perspective, CD4+CD25+ T cells can also reverse an established colitis. CD4+CD25+ T cells proliferate both in the secondary lymphoid organs and at the site of inflammation, suggesting that regulation occurs both locally and systemically. CD4+CD25+ T cells are not only capable of regulating other T cells but are also capable of suppressing components of the innate immune system. Control of colitis is dependent on the presence of the immunosuppressive cytokines interleukin‐10 and transforming growth factor‐β, although their roles are divergent and complex. Regulatory T cells represent one of the hosts mechanisms to prevent immune pathology during chronic immune stimulation. Enhancement of regulatory T‐cell activity may be useful to control autoreactive T‐cell responses and inhibit harmful inflammatory diseases such as asthma and IBD.

The Diagnostic Approach to Monogenic Very Early Onset Inflammatory Bowel Disease

Patients with a diverse spectrum of rare genetic disorders can present with inflammatory bowel disease (monogenic IBD). Patients with these disorders often develop symptoms during infancy or early childhood, along with endoscopic or histological features of Crohns disease, ulcerative colitis, or IBD unclassified. Defects in interleukin-10 signaling have a Mendelian inheritance pattern with complete penetrance of intestinal inflammation. Several genetic defects that disturb intestinal epithelial barrier function or affect innate and adaptive immune function have incomplete penetrance of the IBD-like phenotype. Several of these monogenic conditions do not respond to conventional therapy and are associated with high morbidity and mortality. Due to the broad spectrum of these extremely rare diseases, a correct diagnosis is frequently a challenge and often delayed. In many cases, these diseases cannot be categorized based on standard histological and immunologic features of IBD. Genetic analysis is required to identify the cause of the disorder and offer the patient appropriate treatment options, which include medical therapy, surgery, or allogeneic hematopoietic stem cell transplantation. In addition, diagnosis based on genetic analysis can lead to genetic counseling for family members of patients. We describe key intestinal, extraintestinal, and laboratory features of 50 genetic variants associated with IBD-like intestinal inflammation. In addition, we provide approaches for identifying patients likely to have these disorders. We also discuss classic approaches to identify these variants in patients, starting with phenotypic and functional assessments that lead to analysis of candidate genes. As a complementary approach, we discuss parallel genetic screening using next-generation sequencing followed by functional confirmation of genetic defects.

Early and nonreversible decrease of CD161++/MAIT cells in HIV infection

HIV infection is associated with immune dysfunction, perturbation of immune-cell subsets and opportunistic infections. CD161++ CD8+ T cells are a tissue-infiltrating population that produce IL17A, IL22, IFN, and TNFα, cytokines important in mucosal immunity. In adults they dominantly express the semi-invariant TCR Vα7.2, the canonical feature of mucosal associated invariant T (MAIT) cells and have been recently implicated in host defense against pathogens. We analyzed the frequency and function of CD161++ /MAIT cells in peripheral blood and tissue from patients with early stage or chronic-stage HIV infection. We show that the CD161++ /MAIT cell population is significantly decreased in early HIV infection and fails to recover despite otherwise successful treatment. We provide evidence that CD161++ /MAIT cells are not preferentially infected but may be depleted through diverse mechanisms including accumulation in tissues and activation-induced cell death. This loss may impact mucosal defense and could be important in susceptibility to specific opportunistic infections in HIV.

Monogenic diseases associated with intestinal inflammation: implications for the understanding of inflammatory bowel disease

Inflammatory bowel disease (IBD), encompassing Crohns disease and ulcerative colitis, has multifactorial aetiology with complex interactions between genetic and environmental factors. Over 150 genetic loci are associated with IBD. The genetic contribution of the majority of those loci towards explained heritability is low. Recent studies have reported an increasing spectrum of human monogenic diseases that can present with IBD-like intestinal inflammation. A substantial proportion of patients with those genetic defects present with very early onset of intestinal inflammation. The 40 monogenic defects with IBD-like pathology selected in this review can be grouped into defects in intestinal epithelial barrier and stress response, immunodeficiencies affecting granulocyte and phagocyte activity, hyper- and autoinflammatory disorders as well as defects with disturbed T and B lymphocyte selection and activation. In addition, there are defects in immune regulation affecting regulatory T cell activity and interleukin (IL)-10 signalling. Related to the variable penetrance of the IBD-like phenotype, there is a likely role for modifier genes and gene–environment interactions. Treatment options in this heterogeneous group of disorders range from anti-inflammatory and immunosuppressive therapy to blockade of tumour necrosis factor α and IL-1β, surgery, haematopoietic stem cell transplantation or gene therapy. Understanding of prototypic monogenic ‘orphan’ diseases cannot only provide treatment options for the affected patients but also inform on immunological mechanisms and complement the functional understanding of the pathogenesis of IBD.

Segmented filamentous bacteria in a defined bacterial cocktail induce intestinal inflammation in SCID mice reconstituted with CD45RBhigh CD4+ T cells

Background: The aim was to analyze the influence of intestinal microbiota on the development of intestinal inflammation. We used the model of chronic inflammation that develops spontaneously in the colon of conventional severe combined immunodeficiency (SCID) mice restored with the CD45 RBhigh subset of CD4+T cells isolated from the spleen of normal BALB/c mice. Methods: A CD4+CD45RBhigh subpopulation of T cells was purified from the spleen of conventional BALB/c mice by magnetic separation (MACS) and transferred into immunodeficient SCID mice. Germ‐free (GF) SCID mice or SCID mice monoassociated with Enterococcus faecalis, SFB (segmented filamentous bacteria), Fusobacterium mortiferum, Bacteroides distasonis, and in combination Fusobacterium mortiferum + SFB or Bacteroides distasonis + SFB were used as recipients. SCID mice were colonized by a defined cocktail of specific pathogen‐free (SPF) bacteria. Mice were evaluated 8–12 weeks after the cell transfer for clinical and morphological signs of inflammatory bowel disease (IBD). Results: After the transfer of the CD4+CD45RBhigh T‐cell subpopulation to SCID mice severe colitis was present in conventional animals and in mice colonized with a cocktail of SPF microflora plus SFB. Altered intestinal barrier in the terminal ileum of mice with severe colitis was documented by immunohistology using antibodies to ZO‐1 (zona occludens). Conclusions: Only SFB bacteria together with a defined SPF mixture were effective in triggering intestinal inflammation in the model of IBD in reconstituted SCID mice, while no colitis was detected in GF mice or in mice colonized either with SPF microflora or monoassociated only with SFB or colonized by Bacteroides distasonis + SFB or Fusobacterium mortiferum + SFB. (Inflamm Bowel Dis 2007)

A monoclonal antibody that recognizes a potential coeliac-toxic repetitive pentapeptide epitope in gliadins

Objectives Antibodies that detect coeliac-toxic prolamins from wheat, barley and rye are important tools for controlling the diet of coeliac disease patients. Recently, a monoclonal antibody R5 that recognizes wheat gliadin, barley hordein and rye secalin equally was described. In this study, the epitope recognized by R5 was investigated. Methods Both a phage-displayed heptapeptide library and overlapping peptides spanning the sequence of α- and γ-type gliadins (pepscan) were screened for binding of R5. Results Both techniques yielded comparable pentapeptide consensus sequences (phage display QXPW/FP; pepscan QQPFP). According to recent observations, this peptide stretch may be of key importance in the pathogenicity of coeliac disease. This sequence occurs repetitively in prolamins (in γ- and ω-type prolamins more frequently than in α-type prolamins) together with several homologous peptide stretches, which are recognized less strongly. Conclusions R5 seems to be a good candidate for the specific detection of putative coeliac disease-active sequences in prolamins and thus represents a valuable tool for the quality control of gluten-free food.