Highlights d Inflammatory cues and the microbiota modulate Gpr35 expression across species d LPA modulates GPR35-dependent functions in zebrafish and mouse macrophages d GPR35-expressing macrophages have a protective role during intestinal inflammation d GPR35 controls intestinal inflammation by inducing TNF and corticosterone

Autoimmune/inflammatory intestinal diseases, such as Crohn’s disease and ulcerative colitis, infectious gastrointestinal diseases, and gastrointestinal cancers, such as colorectal cancer, are worldwide a significant health problem. Intercellular communication and direct contact with the environment as the microbiota colonizes the gastrointestinal surface facilitates these diseases. Cytokines mediate the intercellular communication to maintain the equilibrium between host and environment and to regulate immune responses. One cytokine family that exchange information between immune cells and epithelial cells is the IL-20 cytokine family which includes the cytokines IL-19, IL-20, IL-22, IL-24, and IL-26. These cytokines share common receptor subunits and signaling pathways. IL-22 is the most intensively studied cytokine within this family in contexts of gastrointestinal disease, but the importance of other family members is more and more appreciated. In this review, the potential function of IL-20 cytokines concerning gastrointestinal conditions is discussed.

Background: Many patients with moderate to severe Crohn’s disease (CD) are treated with infliximab (IFX). As most of these patients experience a long-lasting therapy, the outcome and withdrawal of IFX treatment are important clinical questions. Methods: In this retrospective study, we analyzed the treatment outcome in moderate to severe CD patients with a steroid-dependent/refractory disease course started on IFX. Withdrawal of IFX was evaluated in patients with deep remission defined as clinical (Harvey-Bradshaw Index ≤4), biochemical (fecal calprotectin [FC] ≤150 μg/g stool) over a period of 2 years, and endoscopic and histological remission before discontinuation of IFX. Results: After induction with IFX, clinical remission was observed in 45/109 patients (41.3%) and clinical response in 61/109 patients (56.0%). Only 8/109 patients (7.3%) achieved deep remission and therefore could be discontinued from IFX therapy. In 4 of these patients (50%), relapse was observed after discontinuation of IFX treatment. FC decreased in these 8 patients in deep remission from 652 ± 168 μg/g stool (mean ± SE) at baseline to 24.9 ± 8.1 μg/g stool at 14 weeks. When compared to patients in deep remission, FC had decreased significantly less at 14 weeks in patients in clinical remission after induction with IFX (n = 31; 154 ± 55 μg/g stool; p = 0.01), in patients with clinical response after induction achieving clinical remission during the maintenance phase (n = 11; 352 ± 67 μg/g stool; p = 0.004), or in patients with chronic active disease course on maintenance therapy (n = 50; 645 ± 93 μg/g stool; p < 0.001). Conclusion: A low discontinuation rate was observed for steroid-dependent/refractory moderate to severe CD patients with IFX treatment. As FC showed a more or less pronounced decrease depending on the response to the IFX treatment, monitoring of FC may become a noninvasive tool for tailoring biological therapy in CD patients.

Goblet cells secrete mucin to create a protective mucus layer against invasive bacterial infection and are therefore essential for maintaining intestinal health. However, the molecular pathways that regulate goblet cell function remain largely unknown. Although GPR35 is highly expressed in colonic epithelial cells, its importance in promoting the epithelial barrier is unclear. In this study, we show that epithelial Gpr35 plays a critical role in goblet cell function. In mice, cell-type-specific deletion of Gpr35 in epithelial cells but not in macrophages results in goblet cell depletion and dysbiosis, rendering these animals more susceptible to Citrobacter rodentium infection. Mechanistically, scRNA-seq analysis indicates that signaling of epithelial Gpr35 is essential to maintain normal pyroptosis levels in goblet cells. Our work shows that the epithelial presence of Gpr35 is a critical element for the function of goblet cell-mediated symbiosis between host and microbiota.

ObjectiveDisruption of the epithelial barrier plays an essential role in developing eosinophilic oesophagitis (EoE), a disease defined by type 2 helper T cell (Th2)-mediated food-associated and aeroallergen-associated chronic inflammation. Although an increased expression of interleukin (IL)-20 subfamily members, IL-19, IL-20 and IL-24, in Th2-mediated diseases has been reported, their function in EoE remains unknown.DesignCombining transcriptomic, proteomic and functional analyses, we studied the importance of the IL-20 subfamily for EoE using patient-derived oesophageal three-dimensional models and an EoE mouse model.ResultsPatients with active EoE have increased expression of IL-20 subfamily cytokines in the oesophagus and serum. In patient-derived oesophageal organoids stimulated with IL-20 cytokines, RNA sequencing and mass spectrometry revealed a downregulation of genes and proteins forming the cornified envelope, including filaggrins. On the contrary, abrogation of IL-20 subfamily signalling in Il20R2−/− animals resulted in attenuated experimental EoE reflected by reduced eosinophil infiltration, lower Th2 cytokine expression and preserved expression of filaggrins in the oesophagus. Mechanistically, these observations were mediated by the mitogen-activated protein kinase (MAPK); extracellular-signal regulated kinases (ERK)1/2) pathway. Its blockade prevented epithelial barrier impairment in patient-derived air–liquid interface cultures stimulated with IL-20 cytokines and attenuated experimental EoE in mice.ConclusionOur findings reveal a previously unknown regulatory role of the IL-20 subfamily for oesophageal barrier function in the context of EoE. We propose that aberrant IL-20 subfamily signalling disturbs the oesophageal epithelial barrier integrity and promotes EoE development. Our study suggests that specific targeting of the IL-20 subfamily signalling pathway may present a novel strategy for the treatment of EoE.