Past project's Collaborator
Amandine MATHIAS (to December 2011)
The precise mechanisms underlying the interaction between intestinal bacteria and the host epithelium lead to multiple consequences that remain poorly understood at the molecular level. Deciphering such events can provide valuable information as to the mode of action of commensal and probiotic microorganisms in the gastrointestinal environment. This project uses intestinal epithelial Caco-2 cell grown as polarized monolayers to show that association of a Lactobacillus or a Bifidobacterium with nonspecific secretory IgA (SIgA) enhanced probiotic adhesion by a factor of 3.4-fold or more. Bacteria alone or in complex with SIgA reinforce transepithelial electrical resistance, and increases phosphorylation of tight junction proteins zonula occludens-1 and occludin. Association with SIgA resulted in both enhances the level of nuclear translocation of NF-kB and production of epithelial polymeric Ig receptor as compared to bacteria alone. Moreover, thymic stromal lymphopoietin production is increased upon exposure to bacteria and further enhanced with SIgA-based complexes, whereas the level of pro-inflammatory epithelial cell mediators remains unaffected. Interestingly, SIgA-mediated potentiation of the Caco-2 cell responsiveness to the two probiotics tested involved Fab-independent interaction with the bacteria. These findings add to the multiple functions of SIgA and underscore a novel role of the antibody in interaction with intestinal bacteria.
A, laser scanning confocal microscopy imaging of the association between fluorescently labeled proteins and the probiotic strain LPR. Right panels, colocalization of bacteria (visualized by differential interference contrast (DIC)) with SIgAC5 and secretory component (SC) is seen as red dots. Control panels are obtained upon DIC-mediated visualization of LPR alone. Scale bars: 10 µm.
B, densitometric analysis of Western blots detecting SC in epithelial cell lysates. Cells were exposed to commensal bacteria alone or in complex with SIgA. Pathonenic S. flexneri was used as a positive control. Significant statistical differences are indicated above the lanes.