Probiotics Restoring the Pattern of Apical Junction Complex Protein (AJC) Expression in the Intestinal Mucosa of Dogs with Inflammatory Bowel Disease

Introduction: The apical junction complex (AJC) plays a significant role in regulating epithelial paracellular permeability. Materials and Methods: We have studied by immunohistochemistry the distribution of tight junction components (claudin-2, occludin) and adherens junction (E-cadherin) proteins in the normal intestinal tract from three control dogs (CD) and from 10 dogs with IBD, before and after a probiotic treatment (VSL#3, VSL Pharmaceuticals, Inc; 450 billion lyophilized bacteria daily for 60 days). Results: In the CD group, occludin-specific labelling was most intense at the epithelial cell AJC and appeared uniformly expressed throughout the epithelium of the small and large intestine, but in the IBD group a weak to absent expression was observed in luminal epithelium and in some intestinal glands of the small intestine. No differences in the distribution or labelling intensity of E-cadherin were observed between normal and affected dogs. In the CD group, claudin-2 was detected in the duodenal epithelium and glands and in the colonic crypt epithelium, decreasing in intensity from the distal to the proximal crypt and becoming barely detectable at the luminal surface of the colon. However, claudin-2 expression was increased in the proximal crypt and luminal epithelium of all dogs with IBD. Conclusions: The observation that the expression and distribution of occludin and claudin-2 were restored after VSL#3 treatment may provide insight into the effects of probiotics on intestinal barrier function.