BACKGROUND: Irritable Bowel Syndrome (IBS) is a common disorder characterized by visceral hypersensitivity and increased intestinal permeability. Abnormalities of gut flora as well as gut immune cells subtype variation have also been observed in IBS. Stress events can affect the onset and course of IBS. Clinical trials showed a beneficial effect of fermented milk (FM) containing Bifidobacterium lactis CNCM-I2494 in constipation predominant IBS (IBS-C) subjects. Recently, we reported that this FM product, dose dependently suppresses visceral hypersensitivity by normalizing intestinal epithelial barrier dysfunctions induced by acute stress in rats. Beside it has been shown that the relief of IBS symptoms by Bifidobacterium. infantis 35624 is associated with normalization in the ratio of proinflammatory/antiinflammatory cytokines IL-12/IL10. Therefore, the aim of this study was to investigate the modulatory effect of FM product containing Bifidobacterium lactis CNCM-I2494 on gut immune barrier impairment promoted by an acute stress in rats. MATERIAL ANDMETHODS: Wistar rats (200-250g) were orally given FM product containing Bifidobacterium lactis CNCM-I2494 for 15 days (1 mL/rat-corresponding to 108 colony forming units of Bifidobacterium lactis CNCM I-2494) or saline. At day 15, paracellular permeability to dextran-FITC (4kD), and transmucosal flux of the protein antigen, horseradish peroxidase 40kD (HRP), were measured in Ussing chamber at different gut levels (ileal Peyer's patches, ileal and colonic segments) in both basal and after 2h of partial restraint stress (PRS) session. Moreover, IL10 and IL12 levels were measured by biochemistry assay on Peyer's patches. RESULTS: In saline treated animals, compared to basal condition, acute stress significantly increased dextran-FITC flux in Peyer's patches and in colonic segment and also substantially increased HRP flux in all gut segments tested as well as in Peyer's patches. FM consumption did not affect the in vitro measured intestinal permeability in basal condition but reduced the increase of both dextran-FITC and HRP flux induced by acute stress. Moreover, in comparison with basal condition, acute stress decreased the ratio of IL10/IL12 in ileal Peyer's patches, illustrating a pro-inflammatory effect. All these stress immune changes were significantly counteracted by 15 days of FM consumption. CONCLUSIONS: These data show in rats, that the consumption of a FM containing Bifidobacterium lactis CNCM-I2494 i) not only reduces the increased gut permeability function but also normalize local immune platform permeability (ileal Payer' patches) altered by acute stress; ii) protects the intestinal immunity barrier by modulating cytokines levels towards an anti-inflammatory profile.