Bai-Sui Feng

Disruption of T-cell immunoglobulin and mucin domain molecule (TIM)–1/TIM4 interaction as a therapeutic strategy in a dendritic cell–induced peanut allergy model

BACKGROUND Recent reports indicate that dendritic cell (DC)-derived T-cell immunoglobulin and mucin domain molecule (TIM)-4 plays an important role in the initiation of T(H)2 polarization. This study aims to elucidate the mechanisms of peanut allergy mediated by microbial products and DCs and the relationship between peanut allergy and TIM4. METHODS Mouse bone marrow-derived DCs (BMDCs) were generated and exposed to cholera toxin (CT) or/and peanut extract (PE) for 24 hours and then adoptively transferred to naive mice. After re-exposure to specific antigen PE, the mice were killed; intestinal allergic status was determined. RESULTS Increased expression of TIM4 and costimulatory molecules was detected in BMDCs after concurrent exposure to CT and PE. Adoptively transferred CT/PE-conditioned BMDCs resulted in the increases in serum PE-specific IgE and skewed T(H)2 polarization in the intestine. Oral challenge with specific antigen PE induced mast cell activation in the intestine. Treating with Toll-like receptor 4 small interfering RNA abolished increased expression of TIM4 and costimulatory molecules by BMDCs. Pretreatment with anti-TIM1 or anti-TIM4 antibody abolished PE-specific T(H)2 polarization and allergy in the intestine. CONCLUSION Concurrent exposure to microbial product CT and food antigen PE increases TIM4 expression in DCs and promotes DC maturation, which plays an important role in the initiation of PE-specific T(H)2 polarization and allergy in the intestine. Modulation of TIM4 production in DCs represents a novel therapeutic approach for the treatment of peanut allergy.

Psychological stress induces eosinophils to produce corticotrophin releasing hormone in the intestine

Background and aims: Psychological stress plays an important role in an array of intestinal disorders. Corticotrophin releasing hormone (CRH) is involved in the pathogenic process induced by psychological stress. The peripheral sources of CRH remain to be further understood. This paper aims to identify the sources of CRH in the intestine. Methods and results: Mice were treated with chronic restraint stress. A double-labelling approach was taken to localise CRH expression in immune cells (including dendritic cells, mast cells, lymphocytes, enterochromaffin cells and eosinophils) in the intestine by confocal microscopy and flow cytometry. As CRH was identified in eosinophils, a cell line of eosinophil, EoL-1 cells were treated with an array of putative stress mediators. The results showed that substance P (SP) induced the expression/release of CRH in eosinophils via neurokinin receptor 1 and 2. Co-culturing SP-primed eosinophils with the mast cell line, HMC-1 cells, we found that HMC-1 cells were activated by eosinophil-derived CRH that further induced T84 monolayer barrier dysfunction, which was further confirmed by a mouse model study. Conclusion: Eosinophils express CRH in the jejunum in response to psychological stress. SP and its receptors mediate the effect of stress in the CRH expression in eosinophils. Eosinophil-derived CRH activates mast cells to induce the jejunum epithelial barrier dysfunction.

Bacterial peptidoglycan breaks down intestinal tolerance via mast cell activation: The role of TLR2 and NOD2

Intestinal microbes are believed to be involved in the pathogenesis of inflammatory bowel disease. Microbes and their products are generally well tolerated by intestinal epithelial cells in the intestinal tract of healthy individuals. It is of significance to understand what breaks down the established tolerance leading to intestinal barrier dysfunction and intestinal inflammation. T84 monolayer transported peptidoglycan (PGN) was determined by enzyme‐linked immune assay. Mast cell line HMC‐1 cell activation in response to PGN stimulation was observed with electron microscopy and measurement of histamine release. T84 monolayer barrier function was determined by recording the transepithelial electric resistance (TER) and measuring the permeability in response to PGN‐induced HMC‐1 cell activation. Expression of Toll‐like receptor (TLR) 2 and nucleotide‐binding oligomerization domain (NOD) 2 were determined by immunocytochemistry, real‐time reverse transcription (RT)‐PCR and Western blot. Exposure to PGN alone did not alter TER and permeability of T84 monolayers. T84 monolayers transported PGN from the apical chamber to the basal chamber of transwell system. TLR2 expressed on the surface of HMC‐1 cells. HMC‐1 cells absorbed PGN. HMC‐1 cells released histamine in response to the PGN stimulation, which was blocked by pretreatment with antibodies or small interfering RNA against TLR2 or NOD2. In a co‐culture system, T84 monolayer transported PGN activated HMC‐1 cells and increased the horseradish peroxidase flux. TLR2 mediated the PGN‐absorption in HMC‐1 cells. Blockade of TLR2 or NOD2 abolished PGN‐induced HMC‐1 cell activation and T84 monolayer barrier dysfunction. T84 monolayer transported PGN activates HMC‐1 cells to release chemical mediators to induce T84 monolayer dysfunction that are mediated by TLR2 and NOD2.

Investigation of the Role of Cholera Toxin in Assisting the Initiation of the Antigen-Specific Th2 Response

Skewed Th2 polarization and tissue mastocytosis are the main features of allergy; but how the antigen-specific Th2 polarization initiated remains unclear. The present study shows that cholera toxin (CT) activates mouse bone marrow mast cells (BMMC) to release interleukin (IL)-4. The activation process involved in Toll-like receptor 4, nucleotide oligomerisation domain 1, activate signal transducer and activator of transcription 6 (STAT6), and IL-4. Activated mast cell-derived IL-4 in synergy with co-existing antigen information provided by dendritic cells drives naïve CD4+ T cells to differentiate into antigen-specific Th2 cells. The finding demonstrates that concurrent exposure to microbial products, such as CT, and antigen-loaded dendritic cells plays a critical role in the initiation of antigen-specific Th2 response in the body; this notion is supported by the concurrent adoptive transfer with CT-pulsed BMMCs and antigen-loaded BMDCs that induced antigen-specific Th2 response and hypersensitivity reaction in the intestine.

Fc Gamma Receptor Signaling in Mast Cells Links Microbial Stimulation to Mucosal Immune Inflammation in the Intestine

Microbes and microbial products are closely associated with the pathogenesis of inflammatory bowel disease (IBD); however, the mechanisms behind this connection remain unclear. It has been previously reported that flagellin-specific antibodies are increased in IBD patient sera. As mastocytosis is one of the pathological features of IBD, we hypothesized that flagellin-specific immune responses might activate mast cells that then contribute to the initiation and maintenance of intestinal inflammation. Thirty-two colonic biopsy samples were collected from IBD patients. A flagellin/flagellin-specific IgG/Fc gamma receptor I complex was identified on biopsied mast cells using both immunohistochemistry and co-immunoprecipitation experiments; this complex was shown to co-localize on the surfaces of mast cells in the colonic mucosa of patients with IBD. In addition, an ex vivo study showed flagellin-IgG was able to bind to human mast cells. These cells were found to be sensitized to flagellin-specific IgG; re-exposure to flagellin induced the mast cells to release inflammatory mediators. An animal model of IBD was then used to examine flagellin-specific immune responses in the intestine. Mice could be sensitized to flagellin, and repeated challenges with flagellin induced an IBD-like T helper 1 pattern of intestinal inflammation that could be inhibited by pretreatment with anti-Fc gamma receptor I antibodies. Therefore, flagellin-specific immune responses activate mast cells in the intestine and play important roles in the pathogenesis of intestinal immune inflammation.

Glucuronoxylomannan promotes the generation of antigen-specific T regulatory cell that suppresses the antigen-specific Th2 response upon activation

T regulatory cells (Treg) have the capability to suppress the skewed immune response, but the generation of antigen (Ag)‐specific Treg for therapeutic purpose is a challenge; the mechanism of Ag‐specific Treg activation remains obscure. Here, we report that glucuronoxylomannan (GXM) is capable of promoting the development of human tolerogenic dendritic cells (DC). GXM‐pulsed DCs increased the expression of forkhead box P3 (Foxp3) in naïve human CD4+CD25− T cells via activating Fc γ receptor IIb and activator protein‐1 and promoting the expression of transforming growth factor β in dendritic cells. Furthermore, the conjugated complex of house dust mite Ag, Dermatophagoides pteronyssinus (Der p) 1, and GXM‐pulsed DCs to drive the naïve human CD4+CD25− T cells to develop into the Der p 1‐specific Tregs, which efficiently suppressed the Ag‐specific Th2 responses. We conclude that GXM‐conjugated specific Ag have the capacity to up‐regulate the tolerogenic property of DCs and promote the generation of Ag‐specific Tregs; the latter can be activated upon the re‐exposure to specific Ag and suppress the skewed Ag‐specific T helper (Th)2 responses.

Expression of integrin alphavbeta6 in the intestinal epithelial cells of patients with inflammatory bowel disease

Background and aims: The prevalence of inflammatory bowel disease (IBD) is about 0.05% in industrialized countries. The pathogenesis of IBD remains to be further understood. The present study aims to elucidate the expression of integrin αvβ6 in the intestinal mucosa of patients with IBD. Materials and Methods: Colonic biopsy was obtained from a group of IBD patients. The expression of αvβ6 in the intestinal mucosa was detected by Western blotting. Human colonic epithelial cell line T84 cells were stimulated by microbial antigen flagellin. The expression of αvβ6 in T84 cells was evaluated by quantitative RT-PCR and Western blotting. Results: The levels of αvβ6 in the intestinal mucosa were much lower than it in normal control subjects. The serum levels of myeloperoxidase (MPO) were higher in IBD patients that were negatively correlated with the levels of αvβ6 in the intestinal mucosa. The expression of αvβ6 was detectable in T84 cells at naοve status that could be upregulated by exposure to microbial antigen flagellin. Pretreatment with MPO dramatically suppressed the expression of αvβ6 in T84 cells. Conclusions: We conclude that the expression of αvβ6 was suppressed in IBD intestinal mucosa, which could be resulted from the high levels of MPO.