The food contaminant fumonisin B1 reduces the maturation of porcine CD11R1+ intestinal antigen presenting cells and antigen-specific immune responses, leading to a prolonged intestinal ETEC infection

Consumption of food or feed contaminated with fumonisin B1 (FB1), a mycotoxin produced by Fusarium verticillioides, can lead to disease in humans and animals. The present study was conducted to examine the effect of FB1 intake on the intestinal immune system. Piglets were used as a target and as a model species for humans since their gastro-intestinal tract is very similar. The animals were orally exposed to a low dose of FB1 (1 mg/kg body weight FB1) for 10 days which did not result in clinical signs. However, when compared to non-exposed animals, FB1-exposed animals showed a longer shedding of F4+ enterotoxigenic Escherichia coli (ETEC) following infection and a lower induction of the antigen-specific immune response following oral immunization. Further analyses to elucidate the mechanisms behind these observations revealed a reduced intestinal expression of IL-12p40, an impaired function of intestinal antigen presenting cells (APC), with decreased upregulation of Major Histocompatibility Complex Class II molecule (MHC-II) and reduced T cell stimulatory capacity upon stimulation. Taken together, these results indicate an FB1-mediated reduction of in vivo APC maturation

CD103 (αE Integrin) Undergoes Endosomal Trafficking in Human Dendritic Cells, but Does Not Mediate Epithelial Adhesion

Dendritic cell (DC) expression of CD103, the α subunit of αEβ7 integrin, is thought to enable DC interactions with E-cadherin-expressing gastrointestinal epithelia for improved mucosal immunosurveillance. In the stomach, efficient DC surveillance of the epithelial barrier is crucial for the induction of immune responses to H. pylori, the causative agent of peptic ulcers and gastric cancer. However, gastric DCs express only low levels of surface CD103, as we previously showed. We here tested the hypothesis that intracellular pools of CD103 in human gastric DCs can be redistributed to the cell surface for engagement of epithelial cell-expressed E-cadherin to promote DC-epithelial cell adhesion. In support of our hypothesis, immunofluorescence analysis of tissue sections showed that CD103+ gastric DCs were preferentially localized within the gastric epithelial layer. Flow cytometry and imaging cytometry revealed that human gastric DCs expressed intracellular CD103, corroborating our previous findings in monocyte-derived DCs (MoDCs). Using confocal microscopy, we show that CD103 was present in endosomal compartments, where CD103 partially co-localized with clathrin, early endosome antigen-1 and Rab11, suggesting that CD103 undergoes endosomal trafficking similar to β1 integrins. Dynamic expression of CD103 on human MoDCs was confirmed by internalization assay. To analyze whether DC-expressed CD103 promotes adhesion to E-cadherin, we performed adhesion and spreading assays on E-cadherin-coated glass slides. In MoDCs generated in the presence of retinoic acid, which express increased CD103, intracellular CD103 significantly redistributed toward the E-cadherin-coated glass surface. However, DCs spreading and adhesion did not differ between E-cadherin-coated slides and slides coated with serum alone. In adhesion assays using E-cadherin-positive HT-29 cells, DC binding was significantly improved by addition of Mn2+ and decreased in the presence of EGTA, consistent with the dependence of integrin-based interactions on divalent cations. However, retinoic acid failed to increase DC adhesion, and a CD103 neutralizing antibody was unable to inhibit DC binding to the E-cadherin positive cells. In contrast, a blocking antibody to DC-expressed E-cadherin significantly reduced DC binding to the epithelium. Overall, these data indicate that CD103 engages in DC-epithelial cell interactions upon contact with epithelial E-cadherin, but is not a major driver of DC adhesion to gastrointestinal epithelia

Lymphocyte migration studies

For maintenance of immunity and tolerance, the organs and tissues of the organism are connected by migrating lymphoid cells. Understanding lymphocyte migration is essential for many disorders and diseases – especially in the mucosa-lined organs. Detailed analyses of migrating lymphocytes have been performed in many species, especially in laboratory animals. However, important experiments in lymphocyte migration have been carried out in large animals, for example sheep, cattle and pigs. These species allow experimental procedures like in situ-organ labelling, lymphocyte retransfusion studies or lymph vessel cannulations. Such studies have made an important contribution to the understanding of the overall principles of lymphocyte migration especially in the mucosal immune system. Major results on the specific migration of naïve and memory T cells through lymphoid organs, the re-distribution of $\gamma$/$\delta$ T cells in the intestinal immune system and the emigration of newly produced B cells from the ileal Peyer’s patches have been obtained in large animals. Since there are growing numbers of markers for large animals, and molecular biology methods are available in these species, experiments in large animals will be an essential tool for the understanding of lymphocyte migration especially in mucosal organs

Lymphocyte migration studies

International audienceFor maintenance of immunity and tolerance, the organs and tissues of the organism are connected by migrating lymphoid cells. Understanding lymphocyte migration is essential for many disorders and diseases - especially in the mucosa-lined organs. Detailed analyses of migrating lymphocytes have been performed in many species, especially in laboratory animals. However, important experiments in lymphocyte migration have been carried out in large animals, for example sheep, cattle and pigs. These species allow experimental procedures like in situ-organ labelling, lymphocyte retransfusion studies or lymph vessel cannulations. Such studies have made an important contribution to the understanding of the overall principles of lymphocyte migration especially in the mucosal immune system. Major results on the specific migration of naïve and memory T cells through lymphoid organs, the re-distribution of $\gamma$/$\delta$ T cells in the intestinal immune system and the emigration of newly produced B cells from the ileal Peyer's patches have been obtained in large animals. Since there are growing numbers of markers for large animals, and molecular biology methods are available in these species, experiments in large animals will be an essential tool for the understanding of lymphocyte migration especially in mucosal organs

The food contaminant fumonisin B1 reduces the maturation of porcine CD11R1+ intestinal dendritic cells, leading to reduced antigen-specific immune responses and a prolonged intestinal ETEC infection

Consumption of food or feed contaminated with fumonisin B1 (FB1), a mycotoxin produced by Fusarium verticillioides, can lead to disease in humans and animals. The present study was conducted to examine the effect of FB1 intake on the intestinal immune system. Piglets were used as a target and as a model species for humans since their gastro-intestinal tract is very similar. The animals were orally exposed to a low dose of FB1 (1 mg/kg body weight FB1) for 10 days which did not result in any clinical signs. However, when compared to non-exposed animals, FB1-exposed animals showed a longer shedding of F4+ enterotoxigenic Escherichia coli (ETEC) following infection and a reduced induction of the antigen-specific immune response following oral immunization. Further analyses to elucidate the mechanisms behind these observations revealed a reduced intestinal expression of IL-12p40 and an impaired function of intestinal dendritic cells, with decreased upregulation of MHC-II and a reduced T cell stimulatory capacity upon stimulation. Taken together, these results indicate an FB1-mediated reduction of in vivo DC maturation

Cholera toxin promotes the generation of semi-mature porcine monocyte-derived dendritic cells that are unable to stimulate T cells

Cholera toxin (Ctx) is a powerful mucosal adjuvant with potential applications for oral vaccination of swine. Dendritic cells (DC) play a key role in the decision between immunity and tolerance, and are likely target cells for mediating Ctx functions in vivo. Therefore, we examined the capacity of Ctx to enhance stimulatory activity of porcine monocyte-derived DC (MoDC). Ctx promoted the development of a semi-mature DC phenotype, with decreased levels of MHC class II and CD40, but increased CD80/86 expression. These changes were associated with activation of extracellular signal-regulated kinase (ERK), but not NF${\kappa}$B or c-Jun N-terminal kinase (JNK). Functionally, Ctx-priming greatly diminished T cell stimulatory capacity both in antigen-specific and superantigen-induced proliferation assays. The lower proliferation rate was not due to increased apoptosis of either DC or T cells. Ctx suppressed TNF${\alpha}$ secretion by MoDC, but induced IL-10 production. The observed effects on T cell proliferation could only be partially mimicked by IL-10 alone. However, addition of recombinant TNF${\alpha}$ to co-cultures of Ctx-primed MoDC and lymphocytes restored lymphocyte proliferation in a concentration-dependent manner. Ctx-primed DC were not actively tolerogenic, since they could not suppress proliferative T cell reactions induced by untreated DC

The food contaminant fumonisin B1 reduces the maturation of porcine CD11R1+ intestinal dendritic cells, resulting in a reduced efficiency of oral immunisation and a prolonged intestinal ETEC infection

Consumption of food or feed contaminated with fumonisin B1 (FB1), a mycotoxin produced by Fusarium verticillioides, can lead to disease in humans and animals. This mycotoxin reduces the efficiency of parenteral vaccinations, indicating that ingestion of FB1-contaminated food suppresses the systemic immune system. The present study was conducted to elucidate the mechanisms by which the mycotoxin FB1 exerts its immunosuppressive effects on the intestinal immune system. Piglets were used as a target and as a model species for humans since their gastrointestinal tracts are very similar both on an anatomical and physiological level. The animals were orally exposed to a low dose of FB1 (1 mg/kg body weight FB1) for 10 days which did not result in any clinical signs. However, when compared to control animals, FB1-exposed animals demonstrated a prolonged excretion of the porcine-specific enteropathogen F4+ enterotoxigenic Escherichia coli (F4+ ETEC) following infection. Upon oral immunisation of piglets with purified F4 fimbriae, FB1 exposure reduced the intestinal antigen-specific immune response as compared to control animals. Further analyses to elucidate the mechanisms behind these observations revealed a reduced expression of IL-12p40 mRNA by intestinal immune cells. Since this cytokine is mainly secreted by antigen presenting cells, we analysed the effects of FB1 on small intestinal CD11R1+ lamina propria dendritic cells (LPDC). These CD11R1+ LPDC matured in response to stimulation with the ETEC-derived virulence factors, F4 fimbriae and flagellin, indicating that this intestinal DC subset is involved in the induction of a protective immunity towards intestinal pathogens. However, in vivo exposure of piglets to FB1 impaired the function of these CD11R1+ LPDC as evidenced by a decreased upregulation of MHCII and the costimulatory molecule CD80/86 upon stimulation with F4 fimbriae and flagellin. Furthermore, the FB1-exposed CD11R1+ LPDC had a reduced T cell stimulatory capacity in an allogeneic myxed lymphocyte reaction. Taken together, these results indicate an FB1-mediated reduction of in vivo DC maturation and stress the need to reduce the exposure of animals and humans to FB1 in order to enhance the efficacy of vaccination programs