TY - JOUR
AU - MD, Richard N. Fedorak,
AB - Background A role for bacterial antigens in the pathogenesis of inflammatory bowel disease (IBD) has been established in enhanced humoral and cellular immune response to ubiquitous antigens of the enteric flora. However, we have recently shown that bacterial antigens in the absence of live bacteria cannot initiate an intestinal inflammation in IBD-prone interleukin (IL)-10 gene-deficient mice. The objective was to investigate whether neonatal exposure to antigens of their own endogenous flora can tolerize mice to bacterial antigens. Methods IL-10 gene-deficient neonates were injected intraperitoneally within 72 hours of birth with a sterile solution of bacterial lysates prepared from fecal material of either conventionally raised mice (contains bacterial antigens) or axenic mice (lacks bacterial antigens). The onset of intestinal inflammation was monitored as the appearance of occult blood in the stool in weekly hemoccult analysis. Mice were sacrificed between age 15 and 19 weeks and tested for histopathologic injury, intestinal inflammation, and systemic response to bacterial antigens. Results In mice neonatally exposed to bacterial antigens the onset of intestinal inflammation was delayed and the incidence of histopathologic injury at age 18 weeks was reduced. In addition, mice injected with lysates from conventionally raised mice exhibited decreased release of proinflammatory cytokines (interferon gamma [IFN-γ] and IL-17) in intestinal tissue and demonstrated reduced bacteria-stimulated systemic responses when compared to mice injected with lysates derived from bacteria-free, axenic mice. Conclusions Neonatal intraperitoneal injection of antigens from the commensal flora causes long-lasting changes in systemic and mucosal immune responses resulting in delayed onset of intestinal inflammation and injury in IBD-prone IL-10 gene-deficient mice. (Inflamm Bowel Dis 2011;) neonatal tolerization, IL-10, inflammatory bowel disease, bacterial antigens, hygiene hypothesis The “hygiene hypothesis” suggests that exposure to common environmental microbial antigens early in life induces protective immune responses that suppress disease onset later in life.1,2 This hypothesis has been used to explain the observation that a variety of sustained inflammatory diseases are more severe and with earlier onset in countries that practice a higher grade of sterility and better hygienic conditions.3 Early exposure to environmental allergens and pathogens is thought to have a tolerizing effect on exposure to these antigens later in life. In support of this hypothesis it has been shown that exposure to stable dust extract prevents allergic hyperresponsiveness in a murine model of allergic asthma.4 Similarly, neonatal exposure with lipopolysaccharide (LPS) and/or allergen can prevent experimental allergic airway disease.5 Neonatal tolerance describes the phenomenon of unresponsiveness to an antigen exposed to as a newborn. It was first described by Owen6 and later experimentally confirmed by Billingham et al.7 Neonatal tolerance is also the basis for many vaccination efforts such as the live attenuated Mycobacteriumbovis vaccine (BCG),8 hepatitis B vaccine (HBV),9 and pertussis vaccine.10 The efficacies of these vaccines provide proof of concept that neonatal tolerance induction to antigens is possible despite the generally impaired function of the developing immune system. The mechanisms for neonatal tolerance are still controversial and may include clonal T-cell deletion and/or inactivation11 as well as active suppression.12,13 Whether bacteria-responsive T cells are undergoing deletion or are under constant suppression has yet to be investigated. It is well acknowledged that components derived from the endogenous flora play a major role in modifying intestinal diseases.14 Bacterial antigens such as peptidoglycans and bacterial proteins have been shown to trigger the intestinal mucosal as well as the systemic immune system, resulting in the generation of antibodies and T-cell responses to bacterial products.15,–19 These humoral and cellular immune responses to products of the enteric micro biota are believed to be a result of lack of tolerance to the endogenous flora during an intestinal inflammatory state.20,21 We have shown previously that acquisition of the endogenous flora leads to a brief immune response to bacterial antigens that may be required for tolerance induction.22 These bacteria-triggered immune responses can lead to transient intestinal inflammation in adult axenic mice following association with endogenous flora, due to a temporary imbalance in intestinal homeostatic cytokine release.23 Healthy wildtype mice return to a state of nonresponsiveness to bacterial antigens within 14 days; in contrast, mice with a genetic defect, such as the lack of cytokines (interleukin [IL]-10 and IL-2), T-cell receptor (TCR) abnormalities (TCRα−/−), and epithelial barrier deficiencies (mdr1a−/−) remain responsive to bacterial antigens.22,24,–28 While luminal microbial antigens are involved in perpetuating intestinal inflammation in susceptible animals, by themselves, i.e., in the absence of live bacteria, these antigens appear to be incapable of initiating an intestinal inflammation in these animals.29 In this study we investigate whether treatment of newborn IL-10 gene-deficient mice with bacterial antigens from the endogenous flora can induce tolerance to further exposure of these antigens and thus modulate the inflammatory response to the endogenous flora in these inflammatory bowel disease (IBD)-susceptible animals. Materials and Methods Mice Homozygous IL-10 gene-deficient mice, generated on C57Bl/6 × 129/SvEv background, were originally obtained from DNAX Research Institute of Molecular and Cellular Biology (Palo Alto, CA) and maintained in a colony at the University of Alberta under specific pathogen-free (SPF) conditions allowing these mice to acquire their endogenous flora at birth. Matings were set up with mice age 10–12 weeks; 129/SvEv mice housed in the same room were used as controls. Preparation of Fecal Antigen Lysates For the preparation of fecal antigen lysates, stool was collected from proximal colon and cecum of sacrificed mice raised under SPF conditions and thus were free of known murine pathogens. For control, stool was collected from mice raised under axenic conditions. Lysates were prepared by treatment of the fecal matter in a miniblender at 5000 rpm in the presence of glass beads according to the method of Dieleman et al,30 modified from that described by Cong et al.18 Lysates were sterilized by passage through a 45-μm filter and aliquots were run on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Visible bands in the preparation from stool of SPF mice that were absent in the preparation of axenic mouse-derived stool verified the presence of bacterial proteins in the SPF preparation, although we cannot exclude that some bands were derived from endogenous proteins produced under the influence of bacterial interaction. Besides bacterial proteins these lysates contain other bacterial components such as cell wall material and nucleic acids. Sterility of both (axenic and SPF) preparations was confirmed using standard aerobic and anaerobic bacterial culture methods. Exposure of Neonates to Fecal Antigen For the injection of fecal lysates, pups born during the last 48–72 hours were temporarily separated from their mothers and split into two groups. The pups were injected intraperitoneally with 100 μL of sterile fecal lysates (2 mg/mL protein concentration) of either SPF or axenic origin using a size 27 (G1/2) needle (Becton Dickinson, Franklin Lakes, NJ). To prevent leakage of the injected liquid, the pups were anesthetized by placing them for 4–5 minutes in a −20° freezer prior to the injection. Pups were revived by warming them under infrared light immediately after injection. Pups belonging to one group were marked to distinguish pups injected with SPF fecal lysates from those injected with axenic fecal lysates in the same litter. To avoid cannibalism by their mothers, pups belonging to one litter were returned together to their mother after all pups had resumed full mobility. Occult Blood Testing Empirically, IL-10 gene-deficient mice in our colony start to develop intestinal inflammation between 8–16 weeks of age. To test for occult blood as a means to monitor the onset of inflammation we daily collected fresh stool samples and subjected them to the guiac-based colorimetric Hemoccult analysis kit (Becton Coulter, Fullerton, CA) starting at 8 weeks of age. Results from 1 week were pooled to minimize the disturbances from inevitable false-positive and false-negative readings. Intestinal Histopathologic Injury Assessment Mice were sacrificed at age 16 and 18 weeks. Colon and cecum were excised, cut longitudinally, and half of each tissue was fixed in 10% formalin. Tissues were then embedded in paraffin, cut, and stained with hematoxylin and eosin (H&E) for light microscopic examination as previously described.22 The slides were scored in a blinded fashion according to a previously published scheme ranging from 0 (no injury) to 10 (maximal injury) as determined by the following four parameters: mucosal ulceration, epithelial hyperplasia, lamina propria mononuclear infiltration, and lamina propria neutrophilic infiltration.31 In Vitro Secretion of Inflammatory Cytokines by Intestinal Tissue The remaining halves of colonic and cecal tissue were washed in phosphate-buffered saline (PBS) and placed in culture wells with 1 mL complete RPMI 1640 medium supplemented with 10% fetal calf serum (FCS) as previously described.22 After 24 hours incubation supernatants and tissue pieces were harvested from the wells and separated by centrifugation. Tissue pieces were weighed and supernatants were assayed for cytokine release with standard enzyme-linked immunosorbent assay (ELISA) techniques using the following cytokine-specific antibodies: anti-IFN-γ clone R4-6A2 and anti-IL-17 clone 18H10.1, as capture antibodies, and biotinylated anti-IFN-γ clone XMG1.2 and anti-IL-17 clone 8H4, as detection antibodies. All antibodies and recombinant cytokine standards were purchased from BD Biosciences (Mississauga, ON, Canada) and were used at pretitered concentrations. In Vitro Systemic T-cell Responses The spleens were removed from sacrificed mice and minced into a single cell suspension in complete RPMI with 10% FCS. Red blood cells were lysed by osmotic shock, and lymphocytes were placed into the wells of 96-well plates at a concentration of 2 × 105 per well in the presence of either bacterial sonicates or the fecal lysates used for injection at a protein concentration of 50 μg/mL. The method for preparation of sonicates from pure bacterial cultures has been described in detail previously.22 Control stimuli included plate-bound anti-CD3ε clone 145-2C11 (PharMingen Canada, Mississauga, ON) and medium alone. After 48 hours of incubation at 37°C in a humidified incubator at 5% CO2, the plates were centrifuged and the amount of interferon gamma (IFN-γ) in the supernatant was quantified by standard ELISA. Fluorescence Analysis To quantify changes in spleen cell composition, single-cell suspensions were prepared in staining buffer consisting of PBS with 2% bovine serum albumin (BSA) and 0.02% NaN3 and incubated for 20–30 minutes on ice with the following monoclonal antibodies (mABs): PE-conjugated anti-CD11b clone M1/70, FITC-conjugated CD45R/B220 clone RA3-6B2, and biotinylated anti-CD3e clone 145-2C11 (all BD Biosciences). Following a washing step cells were incubated for 30 minutes on ice with streptavidin-PE-Cy5 (Cedarlane, Hornby, ON, Canada). The cells were washed, fixed in PBS containing 0.02% NaN3 and 1% paraformaldehyde, and stored at 4°C for flow cytometric analysis. Flow cytometric analysis was performed on a FACScalibur flow cytometer (San Jose, CA) at the University of Alberta Flow Lab. Between 5000 and 10,000 gated events were collected. Statistical Analysis Data are expressed as means ± SEM. Differences between mean values were evaluated using analysis of variance or paired t-tests, where appropriate (SigmaStat, Jandel, San Rafael, CA). Nonparametric data were evaluated using the Mann–Whitney U-test. Results Effect of Neonatal Antigen Exposure on Intestinal Inflammation Delayed Onset of Intestinal Inflammation The critical age to develop spontaneously intestinal inflammation in IL-10 gene-deficient mice in our colony is between 8–16 weeks of age.32 Mice under the age of 8 weeks are histopathologically disease-free. However, the mice demonstrate increased release of proinflammatory cytokines such as IFN-γ and tumor necrosis factor alpha (TNF-α) in colonic and cecal explant cultures at any age. The onset of intestinal injury is marked by changes in stool consistency and by occult blood. To monitor the appearance of occult blood in stool we employed a colorimetric hemoccult assay kit. This assay is based on the peroxidase activity present in the heme portion of hemoglobin. The sensitivity of the assay is 72%. Because the hemoccult test results are not uniformly positive every day for fecal matter collected from a mouse with high injury score, the result of hemoccult analysis were accumulated over a 1-week period. While there was little difference in the percentage of mice with positive hemoccult score in the first weeks tested, the difference became more obvious over time and reached significance from 12 weeks on (Fig. 1). By age 17–18 weeks the difference between mice neonatally injected with axenic fecal lysates from those that received SPF fecal lysates was 28% (P = 0.001). These data demonstrate less occult blood in stool from mice receiving SPF lysates as neonates compared to mice receiving axenic lysates (Fig. 1). Figure 1 View largeDownload slide Occult fecal blood analysis. Groups of 12 mice each were analyzed for occult blood 5 days a week. Hemoccult positive results were recorded as percent of all mice in that group tested during a 1-week period. *p < 0.05 as compared with mice treated with axenic lysates. Figure 1 View largeDownload slide Occult fecal blood analysis. Groups of 12 mice each were analyzed for occult blood 5 days a week. Hemoccult positive results were recorded as percent of all mice in that group tested during a 1-week period. *p < 0.05 as compared with mice treated with axenic lysates. When scored for intestinal injury at age 16 weeks, 10 out of 12 (83.3%) mice that received axenic fecal lysates as neonates displayed high intestinal injury (4 and above) marked by epithelial hyperplasia and cellular infiltrates into the lamina propria (Fig. 2). In contrast, only 4 out of 12 (33.3%) mice receiving SPF fecal lysates as neonates showed histopathologic intestinal injury with a high score at that time. Consistent with this finding, the mean injury score was significantly reduced in these mice compared to axenic lysate-treated mice (Fig. 2). At age 18 weeks the difference in the mean injury scores (6.64 ± 0.75 versus 4.50 ± 0.95) and in the number of mice with high intestinal injury (100% versus 70%) between mice receiving axenic versus those receiving SPF fecal lysates is less pronounced. Supplementary data showing examples of histology scoring from tissues of mice injected with SPF fecal lysates and from those injected with axenic fecal lysates can be accessed online. Figure 2 View largeDownload slide Histopathologic injury score in colon of mice injected as neonates with axenic (black dots) and SPF (gray dots) fecal lysates at age 16 and 18 weeks. Bars represent mean injury score ± SEM. *P < 0.05 as compared with mice injected with axenic fecal lysates analyzed at 16 weeks. Figure 2 View largeDownload slide Histopathologic injury score in colon of mice injected as neonates with axenic (black dots) and SPF (gray dots) fecal lysates at age 16 and 18 weeks. Bars represent mean injury score ± SEM. *P < 0.05 as compared with mice injected with axenic fecal lysates analyzed at 16 weeks. In summary, these data suggest that neonatal exposure of antigens from the endogenous flora delays the onset of intestinal inflammation in the recipient mice. Decreased Cytokine Release in Intestinal Mucosal Tissue IL-10 gene-deficient mice demonstrate increased release of proinflammatory cytokines such as IFN-γ and IL-17 when tested in intestinal explant culture. While axenic IL-10 gene-deficient mice have low baseline levels of proinflammatory cytokines indistinguishable from those of wildtype mice, elevated levels of cytokines can be measured as soon as the mice acquire their intestinal flora.22 Similarly, IL-10 gene-deficient mice injected with axenic fecal lysates demonstrate high levels of IFN-γ and IL-17 (Fig. 3). In contrast, mice that were treated as neonates with SPF lysates produced significantly lesser IFN-γ and IL-17 when tested at age 18 weeks in both colonic and cecal tissues (Fig. 3). A similar reduction in cytokine levels in supernatants from SPF fecal lysate-treated mice compared to those from axenic fecal lysate-treated mice was also found for TNF-α and IL-1β (data not shown). Figure 3 View largeDownload slide Spontaneous release of proinflammatory cytokines during 24 hours in the supernatant of colonic and cecal explant cultures from 18-week-old mice. Data represent the mean ± SEM from duplicate samples for n = 12 mice per group. *P < 0.05 as compared with mice injected with axenic fecal lysates. Figure 3 View largeDownload slide Spontaneous release of proinflammatory cytokines during 24 hours in the supernatant of colonic and cecal explant cultures from 18-week-old mice. Data represent the mean ± SEM from duplicate samples for n = 12 mice per group. *P < 0.05 as compared with mice injected with axenic fecal lysates. Effect of Neonatal Antigen Exposure on Systemic Immune System Reduced Bacterial Antigen-stimulated Systemic Response Healthy wildtype mice are tolerant to stimulation with antigens of their own endogenous flora. Tolerance is acquired following initial exposure to bacterial antigens. Because of the inability to produce a major cytokine involved in immunological homeostasis the IL-10 gene-deficient mouse is defective in establishing a sustained state of tolerance to bacterial antigens at the time of bacterial acquisition. Consequently, IL-10 gene-deficient mice systemically respond to stimulation with antigens derived from the endogenous flora.22 In the same fashion, spleen cells from mice neonatally injected with axenic fecal lysates respond with high IFN-γ release to stimulation with sonicates prepared from pure cultures of endogenous mouse bacterial strains. Figure 4A shows spleen cells stimulated with Lactobacillusreuteri, Bacteroidesvulgatus, and Enterobactercloacae. We chose these bacterial strains because of their known involvement in the intestinal inflammation in IL-10 gene-deficient mice as determined from previous experiments.31,33,34 In contrast to the spleen cell response from mice treated with axenic fecal lysates, the spleen cells from mice treated with SPF fecal lysates demonstrate a significantly reduced IFN-γ response. Likewise, stimulation with SPF lysates, caused reduced IFN-γ release in spleen cells from SPF lysate-treated mice compared to IFN-γ release from spleen cells of axenic lysate-treated mice. Neither spleen cells from SPF nor from axenic lysate-treated mice respond to stimulation with axenic mouse-derived lysates (Fig. 4B). Figure 4 View largeDownload slide IFN-γ release in supernatants of spleen cell cultures derived from 18-week-old mice, stimulated with bacterial sonicates prepared from pure cultures of Lactobacillusreuteri, Bacteroidesvulgatus, and Enterobactercloacae (A) or fecal antigen lysates (B) as determined by ELISA. Values are mean ± SEM from triplicate samples for n = 12 mice per group. *P < 0.02 as compared with mice injected with axenic fecal lysates. Figure 4 View largeDownload slide IFN-γ release in supernatants of spleen cell cultures derived from 18-week-old mice, stimulated with bacterial sonicates prepared from pure cultures of Lactobacillusreuteri, Bacteroidesvulgatus, and Enterobactercloacae (A) or fecal antigen lysates (B) as determined by ELISA. Values are mean ± SEM from triplicate samples for n = 12 mice per group. *P < 0.02 as compared with mice injected with axenic fecal lysates. Changes in Spleen Cell Composition Concomitant with the increase in systemic response to bacterial antigens in untreated IL-10 gene-deficient mice, the composition of various cell types in the spleen is changed (Fig. 5). In healthy wildtype mice the majority of spleen cells are T and B lymphocytes. A minor population (7% in average) consists of CD11b-positive cells. CD11b is a marker that recognizes the alpha M chain which together with the integrin beta 2 chain forms a heterodimer known as macrophage-1 antigen (Mac-1). Mac-1 is expressed at varying levels on the surface of monocytes, granulocytes, macrophages, myeloid-derived dendritic cells, natural killer cells, and activated B cells and is involved in the adhesion and migration of these cells. In IL-10 gene-deficient mice with colitis the populations of B and T lymphocytes is slightly reduced; at the same time CD11b expression increases significantly to a maximum of about 25%. Expression of CD11b in spleens from mice treated with axenic fecal lysates was indistinguishable from that of untreated mice with an average of CD11b-positive cells of 22%. Interestingly, the amount of CD11b-positive cells in IL-10 gene-deficient mice treated with SPF fecal lysates as neonates was found to be increased to an additional 33%. Less than 2% of spleen cells stained double positive for either CD11b/CD3 or CD11b/B220, excluding the likelihood that the expanded CD11b-positive cells are merely activated T or B lymphocytes. Because the actual amount of spleen cells recovered from groups of mice injected with either lysate was similar (3.82 ± 0.83 for mice injected with axenic antigen lysates and 3.52 ± 0.41 for mice injected with SPF antigen lysates), the difference in percentage of CD11b-positive cells between IL-10 gene-deficient mice injected with bacterial antigen-containing SPF lysates as opposed to injected with axenic, nonbacterial antigen lysates marks a factual increase in this activated cell population. Figure 5 View largeDownload slide Staining of spleen cells with markers for T cells (CD3), B cells (B220), and macrophages/monocytes and activated leukocytes (CD11b). Values are mean ± SEM for n = 5–8 mice per group. *P < 0.02 as compared with untreated wildtype mice and **P < 0.01 as compared with mice injected with axenic fecal lysates. Figure 5 View largeDownload slide Staining of spleen cells with markers for T cells (CD3), B cells (B220), and macrophages/monocytes and activated leukocytes (CD11b). Values are mean ± SEM for n = 5–8 mice per group. *P < 0.02 as compared with untreated wildtype mice and **P < 0.01 as compared with mice injected with axenic fecal lysates. Discussion In this study we demonstrate that neonatal exposure to antigens from endogenous fecal flora has long-lasting effects on the mucosal and systemic immune response resulting in reduced inflammatory response to these antigens and a reduction in intestinal inflammation in IBD-prone IL-10 gene-deficient mice. Antigens of the endogenous fecal microbiota are essentially nonself and mucosal, as well as, peripheral tolerance to these antigens has to be established. We have recently demonstrated that normal wildtype mice kept in an axenic environment and then exposed to the endogenous microbiota as adults mount a transitory inflammatory immune response to the bacteria and their antigens resulting in a brief intestinal inflammation. Subsequent establishment of homeostasis appears to be an important step for tolerance induction.23 Newborns have impaired immune responses in both innate35 and adaptive immunity.36 The impermeable placenta does not allow for the transport of macromolecules and/or proteins to the fetus; therefore, the newborn is immunologically naive. In addition, neonates are nearly devoid of peripheral T lymphocytes.37 The first days of life, therefore, represent an important developmental stage where the peripheral T-cell pool is evolving in an essentially lymphopenic environment and freshly generated lymphocytes extensively migrating through nonlymphoid tissue.38 Similarly, in rodents and other mammals the mucosal immune system also develops at birth. This development appears to take place in an organized fashion under the influence of the establishing microbiota.39,40 Because of the symbiotic relationship between this maturing endogenous microbiota and the organism, the evolving immune system is repetitively “boosted” with these endogenous bacterial antigens leading to life-long tolerance and unresponsiveness. However, many genetically modified, IBD-prone rodents are incapable of establishing this life-long tolerance to bacterial antigens of their own endogenous flora. In the case of the IL-10 gene-deficient mouse, insufficient counterbalance of a constant bacterial stimulation, due to the lack of a major regulatory cytokine, directs an infiltration of lymphocytes to the mucosal site and leads to a rise in concentration of inflammatory cytokines causing a fulmonary, intestinal injury by 15–17 weeks of age. Here we show that this process can be delayed and the severity of the inflammatory response can be significantly reduced when the mice are exposed to a myriad of endogenous bacterial components at a timepoint when immune cells start populating the lymphoid and mucosal environment. Exposure to microorganisms and their antigens are considered to be important for the development of immunoregulatory mechanisms. Early childhood infection is thought to establish an immunological balance between proinflammatory and regulatory T-cell responses, thus preventing subsequent responses to microbial and other antigenic stimuli.41,42 Limited antigenic exposure as a result of improved hygiene has been suggested as a cause for the perpetuation of the uncontrolled inflammatory response in IBD patients.43 Results from a study of IBD patients among US Veterans demonstrated that exposure to poor sanitation decreases the future risk of developing Crohn's disease.44 However, contrary to the hygiene hypothesis, some studies suggest that infection early in life could increase risk for disease,45 although timing and type of infection may play an important role.46 Recently, Mazmanian et al47 have demonstrated that a single microbial molecule, polysaccharide A (PSA), in this case derived from the human symbiont Bacteroidesfragilis, was effective in preventing intestinal inflammation in an IBD mouse model. Similarly, an antiinflammatory and IBD-reducing effect was found in the supernatants of Faecalibacteriumprausnitzii cultures.48 The latter observations demonstrate that bacterial components as opposed to live bacteria can also be protective, thus extending the original hygiene hypothesis of the immunomodulatory effect of microbes to cell activating effects of microbial components and products. The mode of action, however, by which microbial antigens mediate immune regulation is not well defined and appears to be variable, dependent on the model and microbial antigen involved. While the effect of Bacteroidesfragilis PSA was found to involve the activation of protective IL-10-producing CD4 T cells, metabolites in the Faecalibacteriumprausnitzii culture supernatants inhibited NF-kB activation and IL-8 production.47,48 Other reported mechanisms involving regulation via PPAR-y and RelA.49 In many cases of IBD protection the regulation is targeted to bacterial antigen-reactive T cells. T cells coming in from the systemic immune system into the intestinal mucosa appear to be already primed.50 Thus, priming of cells infiltrating the gut mucosa may occur in Peyer's patches or in other lymphoid organs such as spleen and lymph nodes via antigens circulating in blood and lymphatic system. Our finding that bacterial antigen-exposure leads to long-lasting suppression of antigen-reactive systemic immune responses in addition to reduced mucosal responses suggests that tolerance induction involves regulation of systemic-activated T cells. To generate and maintain tolerance in neonates various possible mechanisms exist that contribute to the control of T-cell reactivity by either limiting lymphocyte infiltration or by the induction of antigen-specific tolerance in the respective tissue. Regulatory T cells and mucosa-resident intraepithelial lymphocytes (IELs) have been proposed as candidate cells to control gut homeostasis.50,51 The unusual large expansion of CD11b cells we observed in the spleen of the neonatal tolerized mice implicates these cells in the maintenance of tolerance in this model. CD11b+Gr-1+ myeloid-derived suppressor cells (MDCS) have been described that suppress T-cell proliferation and function via depletion of L-arginine.52 Possibly, these cells could reduce the pool of bacterial-antigen primed T cells in a concentration-dependent manner. In accordance with this is our observed decrease in splenic T lymphocytes in tolerized mice. We are currently investigating this hypothesis. In summary, we have shown that early exposure to components of the intestinal microbiota can facilitate tolerance to bacterial antigens and thus reduce IBD development. 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TI - Neonatal exposure to fecal antigens reduces intestinal inflammation
JO - Inflammatory Bowel Diseases
DO - 10.1002/ibd.21453
DA - 2011-04-01
UR - https://www.deepdyve.com/lp/oxford-university-press/neonatal-exposure-to-fecal-antigens-reduces-intestinal-inflammation-E5NzdQOJ0T
SP - 899
EP - 906
VL - 17
IS - 4
DP - DeepDyve
ER -