Different cytokine response of primary colonic epithelial cells to commensal bacteria

AIM: To determine if primary murine colonic epithelial cells (CEC) respond to commensal bacteria and discriminate between different types of bacteria. METHODS: A novel CEC: bacteria co-culture system was used to compare the ability of the colonic commensal bacteria, Bacteroides ovatus, E coli(SLF) and Lactobacillus rhamnosus (LGG) to modulate production of different cytokines (n = 15) by primary CEC. Antibody staining and flow cytometry were used to investigate Toll-like receptor (TLR) expression by CEC directly ex vivo and TLR responsiveness was determined by examining the ability of TLR ligands to influence CEC cytokine production. RESULTS: Primary CEC constitutively expressed functional TLR2 and TLR4. Cultured in complete medium alone, CEC secreted IL-6, MCP-1 and IP-10 the levels of which were significantly increased upon addition of the TLR ligands peptidoglycan (PGN) and lipopolysaccharide (LPS). Exposure to the commensal bacteria induced or up-regulated different patterns of cytokine production and secretion.E coli induced production of MIP-1α/β and p defensin3 whereas B. ovatus and L. rhamnosus exclusively induced MCP-1 and MIP-2α expression, respectively. TNFa, RANTES and MEC were induced or up-regulated in response to some but not all of the bacteria whereas ENA78 and IP-10 were up-regulated in response to all bacteria. Evidence of bacterial interference and suppression of cytokine production was obtained from mixed bacterial: CEC co-cultures. Probiotic LGG suppressed E coli- and B. ovatus-induced cytokine mRNA accumulation and protein secretion. CONCLUSION: These observations demonstrate the ability of primary CEC to respond to and discriminate between different strains of commensal bacteria and identify a mechanism by which probiotic bacteria (LGG) may exert anti-inflammatory effects in vivo.

Production of corticotropin-releasing factor and urocortin from human monocyte-derived dendritic cells is stimulated by commensal bacteria in intestine

AIM: To examine whether commensal bacteria are a contributing cause of stress-related mucosal inflammation.

Corticotropin-releasing factor secretion from dendritic cells stimulated by commensal bacteria

AIM:To study the production and secretion of corticotropin-releasing factor (CRF) by dendritic cells and the influence of commensal bacteria.METHODS:JAWSⅡ cells (ATCC CRL-11904),a mouse dendritic cell line,were seeded into 24-well culture plates and grown for 3 d.Commensal bacterial strains of Clostridium clostrodiiforme (JCM1291),Bacteroides vulgatus (B.vulgatus) (JCM5856),Escherichia coli (JCM1649),or Fusobacterium varium (F.varium) (ATCC8501) were added to the cells except for the control well,and incubated for 2 h.After incubation,we performed enzyme-linked immunosorbent assay for the cultured medium and reverse transcription polymerase chain reaction for the dendritic cells,and compared these values with controls.RESULTS:The level of CRF secretion by control dendritic cells was 40.4±6.2 pg/mL.The CRF levels for cells incubated with F.varium and B.vulgatus were significantly higher than that of the control (P<0.0001).CRF mRNA was present in the control sample without bacteria,and CRF mRNA levels in all samples treated with bacteria were above that of the control sample.F.varium caused the greatest increase in CRF mRNA expression.CONCLUSION:Our results suggest that dendritic cells produce CRF,a process augmented by commensal bacteria.

The Composition of Colonic Commensal Bacteria According to Anatomical Localization in Colorectal Cancer

Colorectal cancer （CRC） is a multistage disease resulting from complex factors, including genetic mutations, epigenetic changes, chronic inflammation, diet, and lifestyle. Recent accumulating evidence suggests that the gut microbiota is a new and important player in the development of CRC. Imbalance of the gut microbiota, especially dysregulated gut bacteria, contributes to colon cancer through mechanisms of inflammation, host defense modulations, oxidative stress, and alterations in bacterial-derived metabolism. Gut commensal bacteria are anatomically defined as four populations： luminal commensal bacteria, mucus-resident bacteria, epithelium-resident bacteria, and lymphoid tissue-resident commensal bacteria. The bacterial flora that are harbored in the gastrointestinal （GI） tract vary both longitudinally and cross-sectionally by different anatomical localization. It is notable that the translocation of colonic commensal bacteria is closely related to CRC progression. CRC-associated bacteria can serve as a noninvasive and accurate biomarker for CRC diagnosis. In this review, we summarize recent findings on the oncogenic roles of gut bacteria with different anatomical localization in CRC progression.

Interactions between commensal bacteria and viral infection:insights for viral disease control in farmed animals

Viral diseases cause serious economic loss in farmed animals industry.However,the efficacy of remedies for viral infection in farmed animals is limited,and treatment strategies are generally lacking for aquatic animals.Interactions of commensal microbiota and viral infection have been studied in recent years,demonstrating a third player in the interaction between hosts and viruses.Here,we discuss recent developments in the research of interactions between commensal bacteria and viral infection,including both promotion and inhibition effect of commensal bacteria on viral pathogenesis,as well as the impact of viral infection on commensal microbiota.The antiviral effect of commensal bacteria is mostly achieved through priming or regulation of the host immune responses,involving differential microbial components and host signaling pathways,and gives rise to various antiviral probiotics.Moreover,we summarize studies related to the interaction between commensal bacteria and viral infection in farmed animals,including pigs,chickens,fish and invertebrate species.Further studies in this area will deepen our understanding of antiviral immunity of farmed animals in the context of commensal microbiota,and promote the development of novel strategies for treatment of viral diseases in farmed animals.

Bacteria,inflammation,and colon cancer

Our relationship with the colonic bacterial flora has long been viewed as benign, but recent studies suggest that this symbiosis has risks as well as benefits. This relationship requires that the host not only provide a supportive environment for the symbiotic bacteria, but also actively maintain intact mechanisms for properly managing the physiologic stresses that are closely associated with the symbiont’s essential survival functions. Failure to do so breaches the host- symbiont contract, and can result in serious effects on the health of the host. Recent investigations that employ several knockout mouse models reveal the consequences of genetic deficiency in the host regarding these mechanisms, and the latent, pro-inflammatory, tumorigenic nature of normal bacterial flora. Further study of the interactions between normal bacterial flora and hosts could shed light on the etiologies and pathogenesis of inflammatory diseases and related cancers, with implications for human health.

Heat stress in pigs and broilers:role of gut dysbiosis in the impairment of the gut-liver axis and restoration of these effects by probiotics,prebiotics and synbiotics

Heat stress is one of the most challenging stressors for animal production due to high economic losses resulting from impaired animal’s productivity,health and welfare.Despite the fact that all farm animal species are susceptible to heat stress,birds and pigs are particularly sensitive to heat stress due to either lacking or non-functional sweat glands.Con-vincing evidence in the literature exists that gut dysbiosis,a term used to describe a perturbation of commensal gut microbiota,develops in broilers and pigs under heat stress.Owing to the protective role of commensal bacteria for the gut barrier,gut dysbiosis causes a disruption of the gut barrier leading to endotoxemia,which contributes to the typical characteristics of heat stressed broilers and growing and growing-finishing pigs,such as reduced feed intake,decreased growth and reduced lean carcass weight.A substantial number of studies have shown that feeding of probiotics,prebiotics and synbiotics is an efficacious strategy to protect broilers from heat stress-induced gut barrier disruption through altering the gut microbiota and promoting all decisive structural,biochemical,and immunologi-cal elements of the intestinal barrier.In most of the available studies in heat stressed broilers,the alterations of gut microbiota and improvements of gut barrier function induced by feeding of either probiotics,prebiotics or synbiot-ics were accompanied by an improved productivity,health and/or welfare when compared to non-supplemented broilers exposed to heat stress.These findings indicate that the restoration of gut homeostasis and function is a key target for dietary interventions aiming to provide at least partial protection of broilers from the detrimental impact of heat stress conditions.Despite the fact that the number of studies dealing with the same feeding strategy in heat stressed pigs is limited,the available few studies suggest that feeding of probiotics might also be a suitable approach to enhance productivity,health and welfare in pigs kept under heat stress conditions.

Therapeutic approaches targeting intestinal microflora in inflammatory bowel disease

Inflammatory bowel diseases, ulcerative colitis, and Crohn＇s disease, are chronic intestinal disorders of unknown etiology in which in genetically susceptible individuals, the mucosal immune system shows an aberrant response towards commensal bacteria. The gastrointestinal tract has developed ingenious mechanisms to coexist with its autologous microflora, but rapidly responds to invading pathogens and then returns to homeostasis with its commensal bacteria after the pathogenic infection is cleared. In case of disruption of this tightly-regulated homeostasis, chronic intestinal inflammation may be induced. Previous studies showed that some commensal bacteria are detrimental while others have either no influence or have a protective action. In addition, each host has a genetically determined response to detrimental and protective bacterial species. These suggest that therapeutic manipulation of imbalance of microflora can influence health and disease. This review focuses on new insights into the role of commensal bacteria in gut health and disease, and presents recent findings in innate and adaptive immune interactions. Therapeutic approaches to modulate balance of intestinal microflora and their potential mechanisms of action are also discussed.

Immunogenic molecules associated with gut bacterial cell walls:chemical structures,immune-modulating functions,and mechanisms

Interactions between gut microbiome and host immune system are fundamental to maintaining the intestinal mucosal barrier and homeostasis.At the host-gut microbiome interface,cell wall-derived molecules from gut commensal bacteria have been reported to play a pivotal role in training and remodeling host immune responses.In this article,we review gut bacterial cell wall-derived molecules with characterized chemical structures,including peptidoglycan and lipid-related molecules that impact host health and disease processes via regulating innate and adaptive immunity.Also,we aim to discuss the structures,immune responses,and underlying mechanisms of these immunogenic molecules.Based on current advances,we propose cell wall-derived components as important sources of medicinal agents for the treatment of infection and immune diseases.

Paneth cells: the hub for sensing and regulating intestinal flora

The complex interplay between symbiotic bacteria and host immunity plays a key role in shaping intestinal homeostasis and maintaining host health. Paneth cells, as one of the major producers of antimicrobial peptides in the intestine under steady-state conditions, play a vital role in regulating intestinal flora. Many studies on inflammatory bowel disease(IBD)-associated genes have put Paneth cells at the center of IBD pathogenesis. In this perspective, we focus on mechanistic studies of different cellular processes in Paneth cells that are regulated by various IBD-associated susceptibility genes, and we discuss the hypothesis that Paneth cells function as the central hub for sensing and regulating intestinal flora in the maintenance of intestinal homeostasis.

Secretory IgA in complex with Lactobacillus rhamnosus potentiates mucosal dendritic cell-mediated Treg cell differentiation via TLR regulatory proteins, RALDH2 and secretion of IL-IO and TGF-β

The importance of secretory IgA in controlling the microbiota is well known, yet how the antibody affects the perception of the commensals by the local immune system is still poorly defined. We have previously shown that the transport of secretory IgA in complex with bacteria across intestinal micmfold cells results in an association with dendritic cells in Peyer＇s patches. However, the consequences of such an interaction on dendritic cell conditioning have not been elucidated. In this study, we analyzed the impact of the commensal Lactobacillus rhamnosus, alone or associated with secretory IgA, on the responsiveness of dendritic cells freshly recovered from mouse Peyer＇s patches, mesenteric lymph nodes, and spleen. Lactobacillus rhamnosus-conditioned mucosal dendritic cells are characterized by increased expression of Toll-like receptor regulatory proteins lincluding single immunoglobulin interleukin-1 receptor-related molecule, suppressor of cytokine signaling 1, and Toll-interacting moleculel and retinaldehyde dehydrogenase 2, low surface expression of co-stimulatory markers, high anti- versus pro-inflammatory cytokine production ratios, and induction of T regulatory cells with suppressive function. Association with secretory IgA enhanced the anti-inflammatory/regulatory Lactobacillus rhamnosus-induced conditioning of mucosal dendritic cells, particularly in Peyer＇s patches. At the systemic level, activation of splenic dendritic cells exposed to Lactobacillus rhamnosus was partially dampened upon association with secretory IgA. These data suggest that secretory IgA, through coating of commensal bacteria, contributes to the conditioning of mucosal dendritic cells toward tolerogenic profiles essential for the maintenance of intestinal homeostasis.