772 Staphylococcal Enterotoxin B Triggers a Bystander Immune Response to Food Antigens Leading to Visceral Hypersensitivity

Background: Bacterial gastroenteritis is a well characterized risk factor to develop irritable bowel syndrome.The mechanism underlying the development of post-infectious irritable bowel syndrome and visceral hypersensitivity (VHS) remains however largely unknown.Previously, we showed that a gastrointestinal infection with Citrobacter rodentium triggers an aberrant immune response to an innocent bystander antigen (ovalbumin, OVA) resulting in mast cell activation and subsequent VHS upon re-exposure to OVA.Here, we hypothesize that not only an active infection but also bacterial products, such as superantigens, are able to trigger such an aberrant immune response leading to activation of mast cells and VHS upon re-exposure to the respective antigen.Material and methods: Three groups of Balb/ c mice were studied (n=8-10/group).Group 1 and 2 received Staphylococcal enterotoxin B (SEB) in the absence (SEB/PBS) or presence (SEB/OVA) of OVA, respectively, during three consecutive days.Group 3 only received OVA dissolved in PBS (PBS/OVA).5 weeks later, all groups received OVA orally every other day.After the 8 th OVA re-exposure, group 2 was randomized to one week treatment with either doxantrazole (mast cell stabilizer) or vehicle.Visceral pain was assessed by recording of the visceromotor response to colorectal distension using abdominal muscle electromyography before OVA re-exposure and after 4, 8 and 12 OVA challenges.VHS was considered when the area under the curve of the responses (normalized to maximum pain at baseline) was >4.56 (=95 th percentile).Thereafter, mice were sacrificed and the colonic permeability was studied in Ussing chambers.Ear swelling was assessed after injection of OVA or saline in the ear to exclude the development of allergy.Results: Re-exposure to OVA (at t=5 weeks) did not affect the visceromotor response to colorectal distention in mice that received SEB/PBS or PBS/OVA (Figure 1).In contrast, all mice that received OVA and SEB developed VHS upon re-exposed to OVA (figure 1).Of note, VHS was reversed in 75% of the doxantrazole compared to 0% in the vehicle treated mice.Moreover, OVA re-exposure increased colonic permeability in SEB/ OVA mice compared to SEB/PBS and PBS/OVA mice, an effect that was reversed by doxantrazole (Figure 2).OVA injection did not cause ear swelling in any group (data not shown).Conclusion: Similar to a bacterial infection, SEB induces an aberrant immune response to innocent bystander antigens, leading to mast cell-mediated VHS and increased mucosal permeability upon re-exposure to the respective antigens.Based on this data, we propose that superantigens, either from microbiota in the nasal cavity or the intestine, may be involved in the pathogenesis of irritable bowel syndrome.Future studies evaluating the presence of these superantigens in patients are therefore warranted.