Claudia Bevilacqua

Intestinal epithelial exosomes carry MHC class II/peptides able to inform the immune system in mice

Background: Intestinal epithelial cells secrete exosome-like vesicles. The aim of this study was to characterise murine intestinal epithelial exosomes and to analyse their capacity to inform the immune system in vivo in mice. Methods: Epithelial exosomes were obtained from the murine epithelial cell line MODE K incubated in the presence or absence of interferon γ (IFN-γ) together with pepsin/trypsin ovalbumin hydrolysate (hOVA) to mimic luminal digestion. Exosomes isolated from MODE K conditioned media (EXO-hOVA and EXO-hOVA-IFN) were characterised by western blot, peptide mapping, and mass spectrometry. They were injected intraperitoneally to C3H/HeN mice to test their immunocompetence. Results: MODE K epithelial exosomes displayed major histocompatibility complex (MHC) class I and class II (upregulated by IFN-γ) molecules and tetraspan proteins (CD9, CD81, CD82) potentially involved in the binding to target cells. A33 antigen, an Ig-like molecule highly specific for intestinal epithelial cells, was enriched in exosomes and was also found in mice mesenteric lymph nodes, suggesting exosome migration towards the gut associated lymphoid tissues. Intraperitoneal injection of EXO-hOVA or EXO-hOVA-IFN did not induce humoral or cellular tolerance to OVA in mice. In contrast, exosomes obtained after incubation with IFN-γ (EXO-hOVA-IFN), bearing abundant MHC class II/OVA complexes, induced a specific humoral immune response. Conclusions: Epithelial exosomes are antigen presenting vesicles bearing MHC class II/peptide complexes that prime for an immunogenic rather than tolerogenic response in the context of a systemic challenge. In the intestine, both the mucosal microenvironment and local effector cells are probably key players in determining the outcome of the immune response to exosome derived epitopes.

Food Allergens Are Protected from Degradation during CD23-Mediated Transepithelial Transport

Background: CD23 (FcΕRII) is expressed by intestinal epithelial cells (IEC) following allergic stimulation and increases the uptake of IgE/allergen complexes. The aim of this study was to further analyze the role of CD23 in the intraepithelial processing of food allergens during transepithelial transport. Methods: Balb-C mice were sensitized intraperitoneally with horseradish peroxidase (HRP) or β-lactoglobulin (β-LG) in the presence of pertussis toxin. In control and sensitized mice, 3H-HRP, intact HRP, or 14C-β-LG fluxes were measured across jejunal segments mounted in Ussing chambers, in the presence or absence of mucosal anti-CD23 antibodies. HPLC analysis of serosal buffer was performed to detect HRP- or β-LG-derived radiolabelled metabolites generated during transepithelial transport. Results: In HRP-sensitized mice, 3H-HRP fluxes and intact HRP fluxes (3,836 ± 476 and 290 ± 86 ng/h ·cm2, respectively) were significantly increased compared to control mice (1,677 ± 297 ng/h · cm2, p < 0.01, and 106 ± 23 ng/h · cm2, p < 0.02, respectively). HPLC analysis indicated the presence of intact HRP in the serosal compartment already 10 min after addition of HRP to the mucosal compartment, a result not observed in the control mice. In the presence of anti-CD23 antibodies, intact HRP fluxes were significantly decreased (131 ± 27 ng/h · cm2) compared to control values in sensitized mice (290 ± 86 ng/h · cm2, p < 0.02), suggesting that CD23 is involved is this ‘protected’ transport pathway. A similar protection during intestinal transport was observed for β-LG in β-LG sensitized mice. Conclusions: These results confirm that CD23 is involved in the rapid transepithelial transport of intact allergens in sensitized animals, and indicate that CD23 opens a ‘protected’ transport pathway in IECs.

Differential Role for CD23 Splice Forms in Apical to Basolateral Transcytosis of IgE/Allergen Complexes

The low affinity receptor for IgE (CD23) was recently implicated in the trans‐epithelial transport of IgE‐allergen complexes from the luminal side of enterocytes in animal models for intestinal allergy. Here, the respective functions of CD23 splice forms, b and bΔ5, in this apical to basolateral transport event have been investigated. First, the new bΔ5 splice form was further characterized, providing evidence that it binds IgE with high affinity, that its expression is induced by sensitization, and that bΔ5, unlike the classical b, undergoes constitutive internalization through clathrin‐coated pits. These results suggested that the two CD23 splice forms were likely involved in different transcytotic events. MDCK cell lines expressing either b or bΔ5 were generated to directly test this hypothesis. In both cell lines, CD23 splice forms were localized at the apical membrane as in enterocytes from sensitized mice. Using mouse monoclonal IgE, we obtained evidence showing that bΔ5 mediates the apical to basolateral transport of free IgE, whereas classical b is much more efficient in mediating the transcytosis of IgE/allergen complexes. The present results shed new light on the role of CD23 species in IgE/allergen transepithelial transport and provide a new powerful physiological tool to study apical to basolateral transcytosis, a process which remains poorly characterized.

Gastric Helicobacter Infection Inhibits Development of Oral Tolerance to Food Antigens in Mice

ABSTRACT The increase in the transcellular passage of intact antigens across the digestive epithelium infected with Helicobacter pylori may interfere with the regulation of mucosal immune responses. The aim of this work was to study the capacity of Helicobacter infection to inhibit the development of oral tolerance or to promote allergic sensitization and the capacity of a gastro-protective agent, rebamipide, to interfere with these processes in mice. Oral tolerance to ovalbumin (OVA) was studied in 48 C3H/He 4-week-old mice divided into four groups: (i) OVA-sensitized mice; (ii) OVA-“tolerized” mice (that is, mice that were rendered immunologically tolerant); (iii) H. felis-infected, OVA-tolerized mice; (iv) and H. felis-infected, OVA-tolerized, rebamipide-treated mice. Oral sensitization to hen egg lysozyme (HEL) was studied in 48 mice divided into four groups: (i) controls; (ii) HEL-sensitized mice; (iii) H. felis-infected, HEL-sensitized mice; and (iv) H. felis-infected, HEL-sensitized, rebamipide-treated mice. Specific anti-OVA or anti-HEL immunoglobulin E (IgE) and IgG1/IgG2a serum titers were measured by enzyme-linked immunosorbent assay. Additionally, the capacity of rebamipide to interfere with antigen presentation and T-cell activation in vitro, as well as absorption of rebamipide across the epithelial monolayer, was tested. H. felis infection led to the inhibition of oral tolerance to OVA, but rebamipide prevented this inhibitive effect of H. felis. H. felis infection did not enhance the sensitization to HEL, but rebamipide inhibited the development of this sensitization. Moreover, rebamipide inhibited in a dose-dependent manner antigen presentation and T-cell activation in vitro and was shown to be able to cross the epithelium at a concentration capable of inducing this inhibitory effect. We conclude that H. felis can inhibit the development of oral tolerance to OVA in mice and that this inhibition is prevented by rebamipide.