Immunomodulation by Bifidobacterium infantis 35624 in the Murine Lamina Propria Requires Retinoic Acid-Dependent and Independent Mechanisms

et al. (2013) Immunomodulation by Bifidobacterium infantis 35624 in the Murine Lamina Propria Requires Retinoic Acid-Dependent and Independent Mechanisms. PLoS ONE 8(5): e62617. doi:10.1371/journal.pone.0062617 Immunomodulation by Bifidobacterium infantis 35624 in the Murine Lamina Propria Requires Retinoic Acid- Dependent and Independent Mechanisms Patrycja Konieczna 0 Ruth Ferstl 0 Mario Ziegler 0 Remo Frei 0 Dirk Nehrbass 0 Roger P. Lauener 0 Cezmi A. Akdis 0 Liam O'Mahony 0 Stefan Bereswill, Charite-University Medicine Berlin, Germany 0 1 Swiss Institute of Allergy and Asthma Research (SIAF), University of Zurich , Davos , Switzerland , 2 Christine Ku hne-Center for Allergy Research and Education (CK-CARE) , Davos , Switzerland , 3 AO Research Institute Davos (ARI) , Davos, Switzerland, 4 Hochgebirgsklinik Davos-Wolfgang, Davos , Switzerland Appropriate dendritic cell processing of the microbiota promotes intestinal homeostasis and protects against aberrant inflammatory responses. Mucosal CD103+ dendritic cells are able to produce retinoic acid from retinal, however their role in vivo and how they are influenced by specific microbial species has been poorly described. Bifidobacterium infantis 35624 (B. infantis) feeding to mice resulted in increased numbers of CD103+retinaldehyde dehydrogenase (RALDH)+ dendritic cells within the lamina propria (LP). Foxp3+ lymphocytes were also increased in the LP, while TH1 and TH17 subsets were decreased. 3,7-dimethyl-2,6-octadienal (citral) treatment of mice blocked the increase in CD103+RALDH+ dendritic cells and the decrease in TH1 and TH17 lymphocytes, but not the increase in Foxp3+ lymphocytes. B. infantis reduced the severity of DSS-induced colitis, associated with decreased TH1 and TH17 cells within the LP. Citral treatment confirmed that these effects were RALDH mediated. RALDH+ dendritic cells decreased within the LP of control inflamed animals, while RALDH+ dendritic cells numbers were maintained in the LP of B. infantis-fed mice. Thus, CD103+RALDH+ LP dendritic cells are important cellular targets for microbiota-associated effects on mucosal immunoregulation. - Funding: The authors are supported by Swiss National Foundation grants (project numbers 32030-132899 and 310030-127356), Christine Ku hne Center for Allergy Research and Education (CK-CARE) and European Union (EU) Marie Curie grants. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have the following conflicts. Liam OMahony is a consultant to Alimentary Health Ltd. Cezmi A. Akdis has received research support from Novartis and Stallergenes and consulted for Actellion, Aventis and Allergopharma. Patrycja Konieczna, Mario Ziegler, Dirk Nehrbass, Remo Frei, Ruth Ferstl and Roger P. Lauener have no conflict of interest. The authors do not have any additional financial or non-financial disclosures, which have not already been described online. This does not alter their adherence to all the PLOS ONE policies on sharing data and materials. The mammalian gastrointestinal microbiota is required for optimal host development and ongoing immune homeostasis [1 3]. The microbiota aids in the digestion of foods, competes with pathogens, degrades mucin and promotes the differentiation of epithelial cells and mucosa-associated lymphoid tissue. In addition, the composition and metabolic activity of the microbiota has profound effects on proinflammatory activity and the induction of immune tolerance by influencing a broad range of mucosal cell types including epithelial cells, dendritic cells, iNKT cells and T lymphocyte subset activity [46]. Gastrointestinal immune homeostasis is dependent on a number of local conditioning factors that reduce pathological proinflammatory responses to non-pathogenic microbes. For example, epithelial-derived cytokines such as TSLP and IL-25 limit dendritic-cell secretion of IL-12 and IL-23, while promoting IL10 secretion [7]. In addition, certain dendritic cell subsets within the mucosa can metabolize vitamin A into retinoic acid, such as the CD103+ dendritic cell subset [8,9]. Retinoic acid is synthesized from stored or dietary retinol by the oxidation of retinol to retinal, followed by oxidation of retinal to retinoic acid. The final step is catalyzed by aldehyde dehydrogenase family 1, subfamily A1 (Aldh1a1) and ALDH1 subfamily A2 (Aldh1a2), also called RALDH enzymes. 3,7-dimethyl-2,6-octadienal (citral) blocks RALDH enzymatic activity. Dendritic cell-derived retinoic acid has dramatic effects on dendritic cell activity and lymphocyte subset plasticity. Retinoic acid can have seemingly conflicting effects on lymphocyte polarization, such as promoting TH17 cells or Treg cells [10]. The promotion of TH17 versus Treg phenotypes may be related to the local concentration of retinoic acid, the dendritic cell subset secreting retinoic acid, the local level of proinflammatory mediators and TGF-b, concomitant toll-like receptor activation or induction of specific microRNA [1114]. So far, the role of specific microbial species in influencing retinoic acid metabolism and CD103+RALDH+ dendritic cells in vivo has been poorly understood. Bifidobacterium longum subsp. infantis 35624 (B. infantis) was originally isolated from resected human healthy gastrointestinal tissue and human clinical studies have demonstrated its efficacy in Irritable Bowel Syndrome patients [15,16]. In addition, murine studies have demonstrated that this microbe protects against inflammatory disorders across a range of inflammatory conditions including colitis, pathogen infection, arthritis and respiratory inflammation [1720]. Previously, in vitro studies with human dendritic cells suggested that promotion of retinoic acid metabolism by B. infantis was a key regulatory feature of this bacterium [21]. In this report, we demonstrate that B. infantis feeding to mice results in increased CD103+RALDH+ dendritic cells within the mucosa, which are responsible for the suppression of TH1 and TH17 lymphocytes and amelioration of dextran sulfate sodium (DSS)-induced colitis. Bacteria and animal models Wild-type C57BL/6 mice were obtained from Charles River and maintained under specific pathogen free conditions. Mice were housed at the AO Research Institute, Davos, Switzerland, in individually ventilated cages for the duration of the study, and all experimental procedures were carried out in accordance with Swiss law. Experimental protocols were approved by the Ethics Committee of the Amt fu r Lebensmittelsicherheit und Tiergesundheit Graubu nden, application number 201115. In the first experiment, three groups of mice were utilized (n = 8 per group). Group 1 did not receive any bacterial supplementation, while groups 2 and 3 were fed B. infantis for 7 days. Each day lyophilized bacteria were resuspended in sterile water to final concentration of 66108 colony forming units (cfu (...truncated)