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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., Mucosal Immunology, 15 (3)

Maintaining intestinal health requires clear segregation between epithelial cells and luminal microbes. The intestinal mucus layer, produced by goblet cells (GCs), is a key element in maintaining the functional protection of the epithelium. The importance of the gut mucus barrier is highlighted in mice lacking Muc2, the major form of secreted mucins. These mice show closer bacterial residence to epithelial cells, develop spontaneous colitis and became moribund when infected with the attaching and effacing pathogen, Citrobacter rodentium. Furthermore, numerous observations have associated GCs and mucus layer dysfunction to the pathogenesis of inflammatory bowel disease (IBD). However, the molecular mechanisms that regulate the physiology of GCs and the mucus layer remain obscured. In this review, we consider novel findings describing divergent functionality and expression profiles of GCs subtypes within intestinal crypts. We also discuss internal (host) and external (diets and bacteria) factors that modulate different aspects of the mucus layer as well as the contribution of an altered mucus barrier to the onset of IBD.

Proton-sensing ovarian cancer G-protein coupled receptor (OGR1) plays an important role in pH homeostasis. Acidosis occurs at sites of intestinal inflammation and can induce endoplasmic reticulum (ER) stress and the unfolded protein response (UPR), an evolutionary mechanism that enables cells to cope with stressful conditions. ER stress activates autophagy, and both play important roles in gut homeostasis and contribute to the pathogenesis of inflammatory bowel disease (IBD). Using a human intestinal epithelial cell model, we investigated whether our previously observed protective effects of OGR1 deficiency in experimental colitis are associated with a differential regulation of ER stress, the UPR and autophagy. Caco-2 cells stably overexpressing OGR1 were subjected to an acidic pH shift. pH-dependent OGR1-mediated signalling led to a significant upregulation in the ER stress markers, binding immunoglobulin protein (BiP) and phospho-inositol required 1α (IRE1α), which was reversed by a novel OGR1 inhibitor and a c-Jun N-terminal kinase (JNK) inhibitor. Proton-activated OGR1-mediated signalling failed to induce apoptosis, but triggered accumulation of total microtubule-associated protein 1 A/1B-light chain 3, suggesting blockage of late stage autophagy. Our results show novel functions for OGR1 in the regulation of ER stress through the IRE1α-JNK signalling pathway, as well as blockage of autophagosomal degradation. OGR1 inhibition might represent a novel therapeutic approach in IBD.

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. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=116 SRC="FIGDIR/small/437264v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@1219637org.highwire.dtl.DTLVardef@cf67corg.highwire.dtl.DTLVardef@10a5026org.highwire.dtl.DTLVardef@13f787_HPS_FORMAT_FIGEXP M_FIG C_FIG

Background & Aims: Hypoxia-associated pathways influence the development of inflammatory bowel disease. Adaptive responses to hypoxia are mediated through hypoxia-inducible factors, which are regulated by iron-dependent hydroxylases. Signals reflecting oxygen tension and iron levels in enterocytes regulate iron metabolism. Conversely, iron availability modulates responses to hypoxia. In the present study we sought to elucidate how iron influences the responses to hypoxia in the intestinal epithelium. Methods: Human subjects were exposed to hypoxia, and colonic biopsy specimens and serum samples were collected. HT-29, Caco-2, and T84 cells were subjected to normoxia or hypoxia in the presence of iron or the iron chelator deferoxamine. Changes in inflammatory gene expression and signaling were assessed by quantitative polymerase chain reaction and Western blot. Chromatin immunoprecipitation was performed using antibodies against nuclear factor (NF)-κB and primers for the promoter of tumor necrosis factor (TNF) and interleukin (IL)1β. Results: Human subjects presented reduced levels of ferritin in the intestinal epithelium after hypoxia. Hypoxia reduced iron deprivation–associated TNF and IL1β expression in HT-29 cells through the induction of autophagy. Contrarily, hypoxia triggered TNF and IL1β expression, and NF-κB activation in Caco-2 and T84 cells. Iron blocked autophagy in Caco-2 cells, while reducing hypoxia-associated TNF and IL1β expression through the inhibition of NF-κB binding to the promoter of TNF and IL1β. Conclusions: Hypoxia promotes iron mobilization from the intestinal epithelium. Hypoxia-associated autophagy reduces inflammatory processes in HT-29 cells. In Caco-2 cells, iron uptake is essential to counteract hypoxia-induced inflammation. Iron mobilization into enterocytes may be a vital protective mechanism in the hypoxic inflamed mucosa. Keywords: Inflammatory Bowel Disease, Autophagy, Deferoxamine, Caco-2

Hypoxia regulates autophagy and nucleotide-binding oligomerization domain receptor, pyrin domain containing (NLRP)3, two innate immune mechanisms linked by mutual regulation and associated to IBD. Here we show that hypoxia ameliorates inflammation during the development of colitis by modulating autophagy and mammalian target of rapamycin (mTOR)/NLRP3 pathway. Hypoxia significantly reduces tumor necrosis factor α, interleukin (IL)-6 and NLRP3 expression, and increases the turnover of the autophagy protein p62 in colon biopsies of Crohn’s disease patients, and in samples from dextran sulfate sodium-treated mice and Il-10 −/− mice. In vitro, NF-κB signaling and NLRP3 expression are reduced through hypoxia-induced autophagy. We also identify NLRP3 as a novel binding partner of mTOR. Dimethyloxalylglycine-mediated hydroxylase inhibition ameliorates colitis in mice, downregulates NLRP3 and promotes autophagy. We suggest that hypoxia counteracts inflammation through the downregulation of the binding of mTOR and NLRP3 and activation of autophagy., Hypoxia and HIF-1α activation are protective in mouse models of colitis, and the latter regulates autophagy. Here Cosin-Roger et al. show that hypoxia ameliorates intestinal inflammation in Crohn’s patients and murine colitis models by inhibiting mTOR/NLRP3 pathway and promoting autophagy.

Clinical studies suggest that pregnant women with elevated iron levels are more vulnerable to develop gestational diabetes mellitus (GDM), but the causes and underlying mechanisms are unknown. We hypothesized that hyperglycemia induces cellular stress responses leading to dysregulated placental iron homeostasis. Hence, we compared the expression of genes/proteins involved in iron homeostasis in placentae from GDM and healthy pregnancies (n = 11 each). RT-qPCR and LC-MS/MS analyses revealed differential regulation of iron transporters/receptors (DMT1/FPN1/ZIP8/TfR1), iron sensors (IRP1), iron regulators (HEPC), and iron oxidoreductases (HEPH/Zp). To identify the underlying mechanisms, we adapted BeWo trophoblast cells to normoglycemic (N), hyperglycemic (H), and hyperglycemic-hyperlipidemic (HL) conditions and assessed Fe3+ -uptake, expression patterns, and cellular pathways involving oxidative stress (OS), ER-stress, and autophagy. H and HL induced alterations in cellular morphology, differential iron transporter expression, and reduced Fe3+ -uptake confirming the impact of hyperglycemia on iron transport observed in GDM patients. Pathway analysis and rescue experiments indicated that dysregulated OS and disturbed autophagy processes contribute to the reduced placental iron transport under hyperglycemic conditions. These adaptations could represent a protective mechanism preventing the oxidative damage for both fetus and placenta caused by highly oxidative iron. In pregnancies with risk for GDM, antioxidant treatment, and controlled iron supplementation could help to balance placental OS levels protecting mother and fetus from impaired iron homeostasis.

Single-nucleotide polymorphisms in the gene encoding G protein-coupled receptor 35 (GPR35) are associated with increased risk of inflammatory bowel disease. However, the mechanisms by which GPR35 modulates intestinal immune homeostasis remain undefined. Here, integrating zebrafish and mouse experimental models, we demonstrate that intestinal Gpr35 expression is microbiota dependent and enhanced upon inflammation. Moreover, murine GPR35

Increasing evidence has indicated that diet and metabolites, including bacteria- and host-derived metabolites, orchestrate host pathophysiology by regulating metabolism, immune system and inflammation. Indeed, autoimmune diseases such as inflammatory bowel disease (IBD) are associated with the modulation of host response to diets. One crucial mechanism by which the microbiota affects the host is signaling through G protein-coupled receptors (GPCRs) termed metabolite-sensing GPCRs. In the gut, both immune and nonimmune cells express GPCRs and their activation generally provide anti-inflammatory signals through regulation of both the immune system functions and the epithelial integrity. Members of GPCR family serve as a link between microbiota, immune system and intestinal epithelium by which all these components crucially participate to maintain the gut homeostasis. Conversely, impaired GPCR signaling is associated with IBD and other diseases, including hepatic steatosis, diabetes, cardiovascular disease, and asthma. In this review, we first outline the signaling, function, expression and the physiological role of several groups of metabolite-sensing GPCRs. We then discuss recent findings on their role in the regulation of the inflammation, their existing endogenous and synthetic ligands and innovative approaches to therapeutically target inflammatory bowel disease.

Les maladies inflammatoires chroniques de l’intestin (MICI) sont des pathologies multifactorielles complexes d’etiologie inconnue. Differentes mutations genetiques, l’exposition a des facteurs environnementaux ou une perte d’homeostasie du microbiote intestinal sont impliques en proportions variables dans la perte de la fonction de barriere de la muqueuse, son invasion par les microorganismes intestinaux et finalement, le declenchement d’une reponse inflammatoire excessive et chronique provoquant les lesions caracteristiques de ces pathologies. Differents composants du systeme immunitaire muqueux comme les cellules epitheliales intestinales, les cellules du systeme immunitaire inne et adaptatif et les mediateurs de l’inflammation sont impliques dans la pathogenese des MICI. D’autres mecanismes cellulaires comme des carences nutritionnelles, l’immuno-recepteur TREM-1 ainsi que l’autophagie amplifient l’inflammation intestinale et accentuent la severite de ces pathologies. Cette revue presente les differents mecanismes impliques dans la physiopathologie des MICI en comparant les muqueuses intestinales saines et pathologiques.

International audience; Background Methyl donor deficiency (MDD) aggravates experimental colitis in rats and increases endoplasmic reticulum (ER) stress through decreased sirtuin 1 (SIRT1) in neuronal cells and myocardium. ER stress plays a key role in IBD pathogenesis.Aim We investigated whether the influence of MDD on colitis resulted from an ER stress response triggered by decreased SIRT1 expression.Design The unfolded protein response (UPR), chaperones proteins, heat shock factor protein 1 (HSF1) and SIRT1 were examined in rats with MDD and dextran sulfate sodium (DSS)-induced colitis in a Caco-2 cell model with stable expression of transcobalamin–oleosin (TO) chimera, which impairs cellular availability of vitamin B12, and in IBD. The effects of SIRT1 activation were studied both in vitro and in vivo.Results MDD aggravated DSS-induced colitis clinically, endoscopically and histologically. MDD activated ER stress pathways, with increased phosphorylate-PKR-like ER kinase, P-eiF-2α, P-IRE-1α, activating transcription factor (ATF)6, XBP1-S protein and ATF4 mRNA expression levels in rats. This was accompanied by reduced SIRT1 expression level and greater acetylation of HSF1, in relation with a dramatic decrease of chaperones (binding immunoglobulin protein (BIP), heat shock protein (HSP)27 and HSP90). Adding either vitamin B12, S-adenosylmethionine or an SIRT1 activator (SRT1720) reduced the UPR in vitro. In rats, SIRT1 activation by SRT1720 prevented colitis by reducing HSF1 acetylation and increasing expression of BIP, HSP27 and HSP90. Immunohistochemistry showed impaired expression of SIRT1 in the colonic epithelium of patients with IBD.Conclusions SIRT1 is a master regulator of ER stress and severity of experimental colitis in case of MDD. It could deserve further interest as a therapeutic target of IBD.

Objectives: We have previously demonstrated an association between gestational diabetes mellitus and dysregulated placental iron transport and regulation. In this context we aimed to investigate the effect of antioxidant treatment to counterbalance the pathophysiological effects of elevated glucose and lipid levels on placental iron homeostasis. Methods: In newly established BeWo-derived cell models, we assessed the time-dependent adaption of trophoblast cells to normoglycemic, hyperglycemic and hyperglycemic combined with hyperlipidemic conditions. During 5 weeks we monitored iron uptake, expression patterns of iron transporters and regulators and cellular responses involving autophagy and oxidative stress pathways. Autophagy markers were analyzed by immunoblotting and oxidative stress by TBARS, total GSH and protein carbonylation assays. In parallel, selenium (Se) supplementation was applied to assess and counteract oxidative stress levels induced by hyperglycemia/ hyperlipidemia. Using qRT-PCR we analyzed 7 genes involved in placental iron homeostasis. The gene expression results were complemented by protein data applying a newly developed mass spectrometry-based method. Results: Elevated glucose levels in BeWo cells altered cellular morphology, affected mRNA and protein expression of iron transporters and regulators, and also reduced iron uptake confirming an impact of hyperglycemia on placental iron transport function. Our results further indicated that increased oxidative stress and changes in the autophagy pathway were involved in altering iron homeostasis under hyperglycemic conditions. Increased antioxidative potential through Se-supplementation was able to completely rescue the adverse effects of hyperglycemia/hyperlipidemia on iron homeostasis. Conclusion: Our data indicate that changes in expression, localization and function of placental iron transporters are responsible for reduced placental iron transport under hyperglycemic conditions. These adaptations could be part of a protective mechanism preventing oxidative damage for both the fetus and the placenta caused by highly oxidative iron. The successful rescue by Se supplementation suggests that antioxidant treatment could protect pregnant women with increased risk to develop GDM by balancing placental oxidative stress levels.

International audience; Evolution led to an essential symbiotic relationship between the host and commensal microbiota, regulating physiological functions including inflammation and immunity. This equilibrium can be disturbed by environmental factors such as lifestyle, diet or antibiotic pressure, contributing to create a dysbiosis. There is much evidence about the gut microbiota's contribution to carcinogenesis, involving pro-inflammatory and immunosuppressive signals. At the same time, it seems to be increasingly clear that commensal microbes can modulate cancer therapy efficacy and safety, in particular, innovating treatments as immune checkpoint inhibitors. In this review, we discuss how the microbiota can promote digestive tract carcinogenesis, responsiveness to cancer therapeutics and cancer-associated complications.

Background and Aims The transcription factor Nrf2 is a major modulator of the cellular antioxidant response. Oxidative burst of infiltrating macrophages leads to a massive production of reactive oxygen species in inflamed tissue of inflammatory bowel disease patients. This oxidative burst contributes to tissue destruction and epithelial permeability, but it is also an essential part of the antibacterial defense. We therefore investigated the impact of the Nrf2 orchestrated antioxidant response in both acute and chronic intestinal inflammation. Methods To study the role of Nrf2 overexpression in mucosal inflammation we used transgenic mice conditionally expressing a constitutively active form of Nrf2 (caNrf2) either in epithelial cells or in the myeloid cell lineage. Acute colitis was induced by dextran sulphate sodium (DSS) in transgenic and control animals and changes in gene expression were evaluated by genome wide expression studies. Long-term effects of Nrf2 activation were studied in mice with an IL-10-/- background. Results Expression of caNrf2 either in epithelial cells or myeloid cells resulted in aggravation of DSS-induced acute colitis. Aggravation of inflammation by caNrf2 was not observed in the IL-10-/- model of spontaneous chronic colitis, where even a trend towards reduced prolapse rate was observed. Conclusions Our findings show that a well balanced redox homeostasis is equally important in epithelial cells as well as myeloid cells during induction of colitis. Aggravation of acute DSS colitis in response to constitutive Nrf2 expression emphasizes the importance of tight regulation of Nrf2 during the onset of intestinal inflammation.

BACKGROUND AND AIMS: During active inflammation tissue intraluminal intestinal pH is decreased in patients with inflammatory bowel disease (IBD). Acidic pH may play a role in IBD pathophysiology. Recently, proton sensing G-protein coupled receptors were identified, including GPR4, OGR1 (GPR68), and TDAG8 (GPR65). We investigated whether GPR4 is involved in intestinal inflammation. METHODS: The role of GPR4 was assessed in murine colitis models: chronic dextran sulphate sodium (DSS) administration and by crossbreeding into an IL-10 deficient background for development of spontaneous colitis. Colitis severity was assessed by body weight, colonoscopy, colon length, histological score, cytokine mRNA expression, and myeloperoxidase (MPO) activity. In the spontaneous Il-10-/- colitis model, the incidence of rectal prolapse and characteristics of lamina propria leukocytes (LPLs) were analyzed. RESULTS: Gpr4-/- mice showed reduced body weight loss and histology score after induction of chronic DSS colitis. In Gpr4-/- /Il-10-/- double knock-outs the onset and progression of rectal prolapse were significantly delayed and mitigated compared to Gpr4+/+ /Il-10-/- mice. Double knock-out mice showed lower histology scores, MPO activity, CD4 + T-helper cell infiltration, IFN-γ, iNOS, MCP-1 (CCL2), CXCL1 and CXCL2 expression compared to controls. In colon, GPR4 mRNA was detected in endothelial cells, some smooth muscle cells, and some macrophages. CONCLUSION: Absence of GPR4 ameliorates colitis in IBD animal models indicating an important regulatory rolein mucosal inflammation, thus providing a new link between tissue pH and the immune system. Therapeutic inhibition of GPR4 may be beneficial for the treatment of IBD.

Deficiency in methyl donor (folate and vitamin B12) and in vitamin D is independently associated with altered bone development. Previously, methyl donor deficiency (MDD) was shown to weaken the activity of nuclear receptor coactivator, peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α), for nuclear signaling in rat pups, including estrogen receptor-α and estrogen-related receptor-α; its effect on vitamin D receptor (VDR) signaling, however, is unknown. We studied bone development under MDD in rat pups and used human MG-63 preosteoblast cells to better understand the associated molecular mechanism. In young rats, MDD decreased total body bone mineral density, reduced tibia length, and impaired growth plate maturation, and in preosteoblasts, MDD slowed cellular proliferation. Mechanistic studies revealed decreased expression of VDR, estrogen receptor-α, PGC1α, arginine methyltransferase 1, and sirtuin 1 in both rat proximal diaphysis of femur and in MG-63, as well as decreased nuclear VDR-PGC1α interaction in MG-63 cells. The weaker VDR-PGC1α interaction could be attributed to the reduced protein expression, imbalanced PGC1α methylation/acetylation, and nuclear VDR sequestration by heat shock protein 90 (HSP90). These together compromised bone development, which is reflected by lowered bone alkaline phosphatase and increased proadipogenic peroxisome proliferator-activated receptor-γ, adiponectin, and estrogen-related receptor-α expression. Of interest, under MDD, the bone development effects of 1,25-dihydroxyvitamin D3 were ineffectual and these could be rescued by the addition of S-adenosylmethionine, which restored expression of arginine methyltransferase 1, PGC1α, adiponectin, and HSP90. In conclusion, MDD inactivates vitamin D signaling via both disruption of VDR-PGC1α interaction and sequestration of nuclear VDR attributable to HSP90 overexpression. These data suggest that vitamin D treatment may be ineffective under MDD.-Feigerlova, E., Demarquet, L., Melhem, H., Ghemrawi, R., Battaglia-Hsu, S.-F., Ewu, E., Alberto, J.-M., Helle, D., Weryha, G., Gueant, J.-L. Methyl donor deficiency impairs bone development via peroxisome proliferator-activated receptor-γ coactivator-1α-dependent vitamin D receptor pathway.

Background and aims An imbalance between cellular antioxidant defence system[s] and reactive oxygen species [ROS]-driven oxidative stress has been implicated in the pathogenesis of inflammatory bowel disease. Peroxiredoxin [PRDX] 6 contributes to an appropriate redox balance by clearing ROS and reducing peroxidized membrane phospholipids. We here studied the role of PRDX6 in acute and chronic dextran sodium sulphate [DSS]-induced colitis. Methods To investigate the impact of PRDX6 on intestinal inflammation, we used wild type [WT], Prdx6 knock-out mice [Prdx6-/-] and transgenic mice [Prdx6tg/tg], overexpressing Prdx6. Acute and chronic colitis was induced by DSS in WT, Prdx6-/- and Prdx6tg/tg mice. Colitis was evaluated by endoscopy, colon length, histopathological assessment and myeloperoxidase [MPO] activity. Changes in mRNA and protein expression of pro-inflammatory cytokines and antioxidant enzymes were evaluated by real-time quantitative polymerase chain reaction [RT-qPCR] and western blot. Total glutathione [GSH] levels in colon samples were determined. Results Prdx6-/- mice exposed to acute and chronic DSS showed a significant decrease in the clinical parameters and in colonic expression of pro-inflammatory cytokines compared with WT mice. mRNA expression of antioxidant enzymes in colon samples was significantly increased in Prdx6-/- compared with WT mice exposed to acute and chronic DSS. In addition, total GSH levels were increased in Prdx6-/- mice treated with DSS in comparison with WT. Overexpression of Prdx6 did not significantly influence acute and chronic colitis. Conclusions Our data indicate that a lack of the antioxidant enzyme PRDX6 protects against the development of acute and chronic experimental colitis and is associated with increased expression and function of other antioxidant enzymes, suggesting effective compensatory mechanisms.

Background Despite medical treatments or surgical options, more than one-third of patients with Crohn's disease suffer from recurring fistulae. Matrix metalloprotease 9 (MMP-9), a type IV collagenase that cleaves components of the extracellular matrix leading to tissue remodeling, is upregulated in crypt abscesses and around fistulae suggesting an important role for this enzyme in fistula formation. Our aims were (1) to correlate serum levels of MMP-9 degradation products in patients with CD with the presence of fistulae and (2) to investigate the impact of selective MMP-9 inhibition in a mouse model of intestinal fibrosis. Methods Serum MMP-9 degradation products were quantified in subjects affected with nonstricturing and nonpenetrating CD (n = 50), stricturing CD (n = 41), penetrating CD (n = 22), CD with perianal fistula (n = 29), and healthy controls (n = 10). Therapeutic efficacy of anti-MMP-9 monoclonal antibodies was assessed in a heterotopic xenograft model of intestinal fibrosis. Results C3M, an MMP-9 degradation product of collagen III, demonstrated the highest serum levels in patients with penetrating CD and differentiated penetrating CD from other CD subgroups and healthy controls, P = 0.0005. Anti-MMP-9 treatments reduced collagen deposition and hydroxyproline content in day-14 intestinal grafts indicating reduced fibrosis. Conclusions The serologic biomarker C3M can discriminate penetrating CD from other CD subgroups and could serve as marker for the development of penetrating CD. Anti-MMP-9 antibody has therapeutic potential to prevent intestinal fibrosis in CD complications.

International audience; Photodynamic therapy (PDT) is currently used as a minimally invasive therapeutic modality for cancer. Whereas antitumor treatment regimens require lethal doses of photosensitizer and light, sublethal doses may have immunomodulatory effects, antibacterial action and/or regenerative properties. A growing body of evidence now indicates that non-lethal PDT doses can alleviate inflammation or treat established soft-tissue infections in various murine models of arthritis, experimental encephalomyelitis, inflammatory bowel disease and chronic skin ulcers. Furthermore, PDT is already used in clinical application and clinical trial for the treatment of psoriasis, chronic wounds and periodontitis in humans. Sublethal PDT should be regarded as a new viable option for the treatment of inflammatory conditions.