Dysregulated balance of retinoid-related orphan receptor γt-dependent innate lymphoid cells is involved in the pathogenesis of chronic DSS-induced colitis

Innate Lymphoid Cells and Intestinal Inflammatory Disorders

Innate lymphoid cells (ILCs) are a population of lymphoid cells that do not express T cell or B cell antigen-specific receptors. They are largely tissue-resident and enriched at mucosal sites to play a protective role against pathogens. ILCs mimic the functions of CD4 T helper (Th) subsets. Type 1 innate lymphoid cells (ILC1s) are defined by the expression of signature cytokine IFN-γ and the master transcription factor T-bet, involving in the type 1 immune response; ILC2s are characterized by the expression of signature cytokine IL-5/IL-13 and the master transcription factor GATA3, participating in the type 2 immune response; ILC3s are RORγt-expressing cells and are capable of producing IL-22 and IL-17 to maintain intestinal homeostasis. The discovery and investigation of ILCs over the past decades extends our knowledge beyond classical adaptive and innate immunology. In this review, we will focus on the roles of ILCs in intestinal inflammation and related disorders.

Effective Barriers: The Role of NKT Cells and Innate Lymphoid Cells in the Gut

The critical role of commensal microbiota in regulating the host immune response has been established. In addition, it is known that host-microbial interactions are bidirectional, and this interplay is tightly regulated to prevent chronic inflammatory disease. Although many studies have focused on the role of classic T cell subsets, unconventional lymphocytes such as NKT cells and innate lymphoid cells also contribute to the regulation of homeostasis at mucosal surfaces and influence the composition of the intestinal microbiota. In this review, we discuss the mechanisms involved in the cross-regulation between NKT cells, innate lymphoid cells, and the gut microbiota. Moreover, we highlight how disruptions in homeostasis can lead to immune-mediated disorders.

Discovery of betulinaldehyde as a natural RORγt agonist

Retinoic Acid Receptor-Related Orphan Receptor γt (RORγt) is a dual-functional therapeutic target. The agonists and inhibitors of RORγt are potential agents for tumor immunotherapy and autoimmune diseases, respectively, and sometimes share similar scaffolds. Although the widely distributed triterpenoid ursolic acid (UA) has been identified as a RORγt inhibitor, the report of a triterpenoid RORγt agonist is still absent. By screening an in-house triterpenoid library, we uncovered a novel RORγt agonist, betulinaldehyde (1), together with an inhibitor (2, 3β, 28-Dihydroxy-lupan-29-oic acid). Compound 1 showed a good RORγt activating effect with the EC₅₀ of 11.4 μM in Alpha Screen assay, and altered the thermal stability of RORγt by directly binding to the protein in vitro. Combined with the SPR assay, the Kd value of compound 1 was examined as 2.99 μM. The modulation mechanism of triterpenoid agonists and inhibitors were discussed by molecular docking. Herein, we firstly discovered compound 1 as a triterpenoid agonist of RORγt. The co-distribution of triterpenoid RORγt agonist and inhibitors in the same plant, might be related to the anti-inflammatory and anti-cancerous bioactivity of the plant extract.

Distinct Alterations in the Composition of Mucosal Innate Lymphoid Cells in Newly Diagnosed and Established Crohn's Disease and Ulcerative Colitis

BACKGROUND AND AIMS

Innate lymphoid cells [ILC] have been suggested to play a role in inflammatory bowel disease [IBD]. Here, we investigated the ILC compartment in intestinal biopsies and blood from distinct patient groups with Crohn's disease [CD] and ulcerative colitis [UC], either newly diagnosed or with disease established for at least 1 year. This approach allowed us to simultaneously investigate temporal, disease-specific, and tissue-specific changes in ILC composition in IBD.

METHODS

ILC subset frequencies, phenotype, and transcription factor profile in blood and intestinal biopsies were investigated by multi-parameter flow cytometry analysis. Endoscopic disease severity was judged using the ulcerative colitis endoscopic index of severity and the simple endoscopic score for Crohn's disease.

RESULTS

The frequency of NKp44+ILC3 was decreased in inflamed tissue, both in patients with CD and those with UC, already at the time of diagnosis, and correlated with disease severity. Simultaneously, the frequency of ILC1 was increased in patients with CD, whereas the frequency of ILC2 was increased in patients with UC. However, in patients with established UC or CD, both ILC1 and ILC2 were increased. In contrast to the ILC composition in inflamed tissue, ILC in non-inflamed tissue or blood were unchanged compared with non-IBD controls. Finally, in patients undergoing treatment with an anti-α4β7 antibody the frequencies of ILC in peripheral blood remained unchanged.

CONCLUSIONS

We report both shared and distinct changes in ILC composition depending on diagnosis and disease duration. The alterations in ILC composition in IBD occur selectively at inflamed sites in the gut.

Innate lymphoid cells in antitumor immunity

Innate lymphoid cells (ILCs) are the most recently characterized subset of innate lymphocytes. Based on their specific transcriptional regulation, cytokine secretion pattern and effector functions ILCs mirror the different CD4 T helper cell subsets, with the unique attributes of acting locally in early phases of immune responses, in an antigen-independent manner. In this review, we discuss how ILCs have been implicated in tumorigenesis. Their presence might favor or inhibit tumor growth, depending on the cytokines released and the specific tumor microenvironment. As our understanding of ILCs' contribution to antitumor responses advances, clinical options to target ILCs in antitumor therapies are also emerging.

Update on pathogenesis and predictors of response of therapeutic strategies used in inflammatory bowel disease

The search for biomarkers that characterize specific aspects of inflammatory bowel disease (IBD), has received substantial interest in the past years and is moving forward rapidly with the help of modern technologies. Nevertheless, there is a direct demand to identify adequate biomarkers for predicting and evaluating therapeutic response to different therapies. In this subset, pharmacogenetics deserves more attention as part of the endeavor to provide personalized medicine. The ultimate goal in this area is the adjustment of medication for a patient’s specific genetic background and thereby to improve drug efficacy and safety rates. The aim of the following review is to utilize the latest knowledge on immunopathogenesis of IBD and update the findings on the field of Immunology and Genetics, to evaluate the response to the different therapies. In the present article, more than 400 publications were reviewed but finally 287 included based on design, reproducibility (or expectancy to be reproducible and translationable into humans) or already measured in humans. A few tests have shown clinical applicability. Other, i.e., genetic associations for the different therapies in IBD have not yet shown consistent or robust results. In the close future it is anticipated that this, cellular and genetic material, as well as the determination of biomarkers will be implemented in an integrated molecular diagnostic and prognostic approach to manage IBD patients.

A breakthrough in probiotics: Clostridium butyricum regulates gut homeostasis and anti-inflammatory response in inflammatory bowel disease

Intestinal immune homeostasis is regulated by gut microbiota, including beneficial and pathogenic microorganisms. Imbalance in gut bacterial constituents provokes host proinflammatory responses causing diseases such as inflammatory bowel disease (IBD). The development of next-generation sequencing technology allows the identification of microbiota alterations in IBD. Several studies have shown reduced diversity in the gut microbiota of patients with IBD. Advances in gnotobiotic technology have made possible analysis of the role of specific bacterial strains in immune cells in the intestine. Using these techniques, we have shown that Clostridium butyricum as a probiotic induces interleukin-10-producing macrophages in inflamed mucosa via the Toll-like receptor 2/myeloid differentiation primary response gene 88 pathway to prevent acute experimental colitis. In this review, we focus on the new approaches for the role of specific bacterial strains in immunological responses, as well as the potential of bacterial therapy for IBD treatments.

Cross-talk between RORγt+ innate lymphoid cells and intestinal macrophages induces mucosal IL-22 production in Crohn's disease

BACKGROUND

Interleukin (IL)-22-producing RORγt innate lymphoid cells (ILCs) play a pivotal role in intestinal immunity. Recent reports demonstrated that ILCs contribute to mucosal protection and intestinal inflammation in mice. In humans, numbers of RORγt ILCs are significantly increased in the intestine of patients with Crohn's disease (CD), suggesting that ILCs may be associated with intestinal inflammation in CD. However, the mechanism by which ILCs are regulated in the intestine of patients with CD is poorly understood. This study aimed to determine the activation mechanism of intestinal ILCs in patients with CD.

METHODS

CD45 lineage marker ILCs were isolated from intestinal lamina propria of patients with CD. ILCs were then subdivided into 4 distinct populations based on the expression of CD56 and CD127. Purified ILC subsets were cocultured with intestinal CD14 macrophages, and IL-22 production was evaluated.

RESULTS

CD127CD56 and CD127CD56 ILC, but not CD127CD56 or CD127CD56 ILC, subsets expressed RORγt and produced IL-22. IL-22 production by these ILC subsets was enhanced when ILCs were cocultured with intestinal macrophages. IL-23 or cell-to-cell contact was required for macrophage-mediated activation of ILCs. IL-22 production by ILCs was perturbed in inflamed mucosa compared with noninflamed mucosa. IL-22 induced the expression of Reg1α and Claudin-1 in human intestinal epithelial organoids.

CONCLUSIONS

RORγt ILCs might enhance mucosal barrier function through the upregulation of Reg1α through production of IL-22. Although CD14 macrophages augment intestinal inflammation in patients with CD, macrophages also promote a negative feedback pathway through the activation of IL-22 production by RORγt ILCs.

Insights from immunology: new targets for new drugs?

Rapid advances in our understanding of inflammatory bowel diseases have resulted from the synthesis of data from experimental and genetic studies. These have suggested a wide range of potential immunological targets with both local and systemic scope. Drugs to several of these targets have now reached phase I/II studies, and are discussed in the context of their scientific rationale. However, despite the advent of new classes of therapeutics targeting cellular trafficking and intracellular mediators of cytokine signalling, the armamentarium of effective therapeutics remains sparse. Only with more detailed experimental medicine studies will this imbalance be resolved.

Mechanisms of innate lymphoid cell and natural killer T cell activation during mucosal inflammation

Mucosal surfaces in the airways and the gastrointestinal tract are critical for the interactions of the host with its environment. Due to their abundance at mucosal tissue sites and their powerful immunomodulatory capacities, the role of innate lymphoid cells (ILCs) and natural killer T (NKT) cells in the maintenance of mucosal tolerance has recently moved into the focus of attention. While NKT cells as well as ILCs utilize distinct transcription factors for their development and lineage diversification, both cell populations can be further divided into three polarized subpopulations reflecting the distinction into Th1, Th2, and Th17 cells in the adaptive immune system. While bystander activation through cytokines mediates the induction of ILC and NKT cell responses, NKT cells become activated also through the engagement of their canonical T cell receptors (TCRs) by (glyco)lipid antigens (cognate recognition) presented by the atypical MHC I like molecule CD1d on antigen presenting cells (APCs). As both innate lymphocyte populations influence inflammatory responses due to the explosive release of copious amounts of different cytokines, they might represent interesting targets for clinical intervention. Thus, we will provide an outlook on pathways that might be interesting to evaluate in this context.

Interleukin 23 in Crohn's disease

: Crohn's disease (CD) is a lifelong inflammatory condition with underlying environmental and genetic components. CD affects multiple parts of the gastrointestinal tract, and it has a growing incidence in Western societies. IL-23 receptor variants have been identified as susceptibility or resistance factors for CD in genome-wide association studies. Accordingly, IL-23 is required for the development of experimental inflammatory bowel disease in many murine models. IL-23 receptor is expressed by both innate and adaptive immune cells, which include Th17, natural killer T, γδ T cells, and RORγt innate lymphoid cells all of which are capable of secreting IL-17A, IL-17F, IL-22, and interferon-γ upon IL-23 stimulation. During the past decade, pathogenic and protective roles have been described for these cytokines in the inflammatory bowel disease pathogenesis. More recently, innate lymphoid cells have been implicated in disease development. In this review, we have summarized and discussed these findings with an emphasis not only on the contribution of Th17 but also on innate lymphoid cells to disease etiology.

Macrophages and dendritic cells emerge in the liver during intestinal inflammation and predispose the liver to inflammation

The liver is a physiological site of immune tolerance, the breakdown of which induces immunity. Liver antigen-presenting cells may be involved in both immune tolerance and activation. Although inflammatory diseases of the liver are frequently associated with inflammatory bowel diseases, the underlying immunological mechanisms remain to be elucidated. Here we report two murine models of inflammatory bowel disease: RAG-2^−/− mice adoptively transferred with CD4⁺CD45RB^high T cells; and IL-10^−/− mice, accompanied by the infiltration of mononuclear cells in the liver. Notably, CD11b⁻CD11c^lowPDCA-1⁺ plasmacytoid dendritic cells (DCs) abundantly residing in the liver of normal wild-type mice disappeared in colitic CD4⁺CD45RB^high T cell-transferred RAG-2^−/− mice and IL-10^−/− mice in parallel with the emergence of macrophages (Mφs) and conventional DCs (cDCs). Furthermore, liver Mφ/cDCs emerging during intestinal inflammation not only promote the proliferation of naïve CD4⁺ T cells, but also instruct them to differentiate into IFN-γ-producing Th1 cells in vitro. The emergence of pathological Mφ/cDCs in the liver also occurred in a model of acute dextran sulfate sodium (DSS)-induced colitis under specific pathogen-free conditions, but was canceled in germ-free conditions. Last, the Mφ/cDCs that emerged in acute DSS colitis significantly exacerbated Fas-mediated hepatitis. Collectively, intestinal inflammation skews the composition of antigen-presenting cells in the liver through signaling from commensal bacteria and predisposes the liver to inflammation.