Prof Fiona Powrie FRS
|Scientific Themes:||Immunology & Infectious Disease|
The gastrointestinal tract is one of the major sites of immunological challenge to the host immune system. Here the host must be able to mount protective immune responses against invading pathogenic micro-organisms while, at the same time specifically not activating these mechanisms in response to dietary antigens or normal enteric flora. In the intestine, therefore, perhaps more than any other organ, immune reactivity must be tightly regulated to ensure induction of protective and not pathologic responses.
The research interests of the group involve characterisation of the cellular and molecular pathways that control intestinal homeostasis and how these break down in inflammatory bowel disease and colon cancer.
Main areas of research:
- Analysis of innate responses to intestinal bacteria and how these influence the adaptive immune response
- Characterisation of intestinal dendritic cell subsets and their contribution to tolerance and immunity in the gut
- Regulatory T cells and their induction, specificity and function in the intestine
- Identification of cytokines and downstream signalling pathways that promote intestinal inflammation with particular emphasis on the IL-23/Th-17 immune axis
- Susceptibility genes that control bacteria-driven colon cancer
|Kevin Maloy||Sir William Dunn School of Pathology||United Kingdom|
|John O'Shea||National Institute of Arthritis and Musculoskeletal and Skin Diseases||United States|
|Dan Cua||Schering Plough Research Institute||United States|
EMBO Mol Med, 4 (2), pp. 71-74. | Read more2012. Gut reactions: immune pathways in the intestine in health and disease.
Intestinal homeostasis depends on complex interactions between the microbiota, the intestinal epithelium and the host immune system. Diverse regulatory mechanisms cooperate to maintain intestinal homeostasis, and a breakdown in these pathways may precipitate the chronic inflammatory pathology found in inflammatory bowel disease. It is now evident that immune effector modules that drive intestinal inflammation are conserved across innate and adaptive leukocytes and can be controlled by host regulatory cells. Recent evidence suggests that several factors may tip the balance between homeostasis and intestinal inflammation, presenting future challenges for the development of new therapies for inflammatory bowel disease. Hide abstract
Results of experimental and genetic studies have highlighted the role of the IL-23/IL-17 axis in the pathogenesis of inflammatory bowel disease (IBD). IL-23-driven inflammation has been primarily linked to Th17 cells; however, we have recently identified a novel population of innate lymphoid cells (ILCs) in mice that produces IL-17, IL-22, and IFN-γ in response to IL-23 and mediates innate colitis. The relevance of ILC populations in human health and disease is currently poorly understood. In this study, we have analyzed the role of IL-23-responsive ILCs in the human intestine in control and IBD patients. Our results show increased expression of the Th17-associated cytokine genes IL17A and IL17F among intestinal CD3⁻ cells in IBD. IL17A and IL17F expression is restricted to CD56⁻ ILCs, whereas IL-23 induces IL22 and IL26 in the CD56⁺ ILC compartment. Furthermore, we observed a significant and selective increase in CD127⁺CD56⁻ ILCs in the inflamed intestine in Crohn's disease (CD) patients but not in ulcerative colitis patients. These results indicate that IL-23-responsive ILCs are present in the human intestine and that intestinal inflammation in CD is associated with the selective accumulation of a phenotypically distinct ILC population characterized by inflammatory cytokine expression. ILCs may contribute to intestinal inflammation through cytokine production, lymphocyte recruitment, and organization of the inflammatory tissue and may represent a novel tissue-specific target for subtypes of IBD. Hide abstract
Mutations in the IL23R gene are linked to inflammatory bowel disease susceptibility. Experimental models have shown that interleukin-23 (IL-23) orchestrates innate and T cell-dependent colitis; however, the cell populations it acts on to induce intestinal immune pathology are unknown. Here, using Il23r(-/-) T cells, we demonstrated that T cell reactivity to IL-23 was critical for development of intestinal pathology, but not for systemic inflammation. Through direct signaling into T cells, IL-23 drove intestinal T cell proliferation, promoted intestinal Th17 cell accumulation, and enhanced the emergence of an IL-17A(+)IFN-gamma(+) population of T cells. Furthermore, IL-23R signaling in intestinal T cells suppressed the differentiation of Foxp3(+) cells and T cell IL-10 production. Although Il23r(-/-) T cells displayed unimpaired Th1 cell differentiation, these cells showed impaired proliferation and failed to accumulate in the intestine. Together, these results highlight the multiple functions of IL-23 signaling in T cells that contribute to its colitogenic activity. Hide abstract
STAT3, an essential transcription factor with pleiotropic functions, plays critical roles in the pathogenesis of autoimmunity. Despite recent data linking STAT3 with inflammatory bowel disease, exactly how it contributes to chronic intestinal inflammation is not known. Using a T cell transfer model of colitis, we found that STAT3 expression in T cells was essential for the induction of both colitis and systemic inflammation. STAT3 was critical in modulating the balance of T helper 17 (Th17) and regulatory T (Treg) cells, as well as in promoting CD4(+) T cell proliferation. We used chromatin immunoprecipitation and massive parallel sequencing (ChIP-Seq) to define the genome-wide targets of STAT3 in CD4(+) T cells. We found that STAT3 bound to multiple genes involved in Th17 cell differentiation, cell activation, proliferation, and survival, regulating both expression and epigenetic modifications. Thus, STAT3 orchestrates multiple critical aspects of T cell function in inflammation and homeostasis. Hide abstract
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-gamma in the colon. Stimulation of colonic leukocytes with IL-23 induced the production of IL-17 and interferon-gamma exclusively by innate lymphoid cells expressing Thy1, stem cell antigen 1 (SCA-1), retinoic-acid-related orphan receptor (ROR)-gammat 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-gammat, 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. Hide abstract
The immune response in the gastrointestinal tract is a tightly controlled balance between effector and regulatory cell responses. Here, we have investigated the role of OX40 in influencing the balance between conventional T cells and Foxp3+ regulatory T (T reg) cells. Under steady-state conditions, OX40 was required by T reg cells for their accumulation in the colon, but not peripheral lymphoid organs. Strikingly, under inflammatory conditions OX40 played an essential role in T reg cell-mediated suppression of colitis. OX40(-/-) T reg cells showed reduced accumulation in the colon and peripheral lymphoid organs, resulting in their inability to keep pace with the effector response. In the absence of OX40 signaling, T reg cells underwent enhanced activation-induced cell death, indicating that OX40 delivers an important survival signal to T reg cells after activation. As OX40 also promoted the colitogenic Th1 response, its expression on T reg cells may be required for effective competition with OX40-dependent effector responses. These results newly identify a key role for OX40 in the homeostasis of intestinal Foxp3+ T reg cells and in suppression of colitis. These fi ndings should be taken into account when considering OX40 blockade for treatment of IBD. Hide abstract
The immune system is pivotal in mediating the interactions between host and microbiota that shape the intestinal environment. Intestinal homeostasis arises from a highly dynamic balance between host protective immunity and regulatory mechanisms. This regulation is achieved by a number of cell populations acting through a set of shared regulatory pathways. In this review, we summarize the main lymphocyte subsets controlling immune responsiveness in the gut and their mechanisms of control, which involve maintenance of intestinal barrier function and suppression of chronic inflammation. CD4(+)Foxp3(+) T cells play a nonredundant role in the maintenance of intestinal homeostasis through IL-10- and TGF-beta-dependent mechanisms. Their activity is complemented by other T and B lymphocytes. Because breakdown in immune regulatory networks in the intestine leads to chronic inflammatory diseases of the gut, such as inflammatory bowel disease and celiac disease, regulatory lymphocytes are an attractive target for therapies of intestinal inflammation. Hide abstract
Characterization of commensal bacteria reactive T cells in IBD
The gastrointestinal tract in humans is colonised by an abundant and diverse array of bacteria which exist in a mutually beneficial relationship with the host, promoting health. In the inflammatory bowel diseases (IBDs) this peaceful relationship breaks down with the development of damaging inflammatory response to our bacterial residents.CD4+ T cells in the intestine contribute to host defense but in IBD there is a more pathogenic and inflammatory polyfunctional T cell response involving ...
Genetic and functional analysis of inflammation-driven colon cancer
Microbe- induced inflammatory pathways are important drivers of carcinogenesis in malignancies like Helicobacter pylori– induced gastric cancer and colitis- associated colon cancer (CAC) in inflammatory bowel disease (IBD). However the immune cells and cytokines that mediate the transition from colitis to colon cancer are poorly understood. We have recently described a novel model of bacteria-driven colon cancer and identified a genetic locus that controls cancer susceptibility. Mechanistic ...
Molecular analysis of the IL-23 receptor pathway in chronic intestinal inflammation
The inflammatory bowel diseases are chronic debilitating inflammatory diseases (IBD) of the gastrointestinal tract. In IBD the normal peaceful relationship between the immune system and bacteria in the intestine breaks down with the development of damaging inflammatory responses in the bowel. Studies in model systems have revealed a pivotal role for the cytokine IL-23 in the development of chronic intestinal inflammation. IL-23 plays an important role in promoting Th17 responses in vivo and ...