Enterotoxigenic Escherichia coli(ETEC) are important intestinal pathogens that cause diarrhea in humans and animals.Although probiotic bacteria may protect against ETEC-induced enteric infections,the underlying mechanisms are unknown.In this study,porcine intestinal epithelial J2 cells(IPEC-J2) were pre-incubated with and without Lactobacillus rhamnosus ATCC 7469 and then exposed to F4+ ETEC.Increases in TLR4 and NOD2 mRNA expression were observed at 3 h after F4+ ETEC challenge,but these increases were attenuated by L.rhamnosus treatment.Expression of TLR2 and NOD1 mRNA was upregulated in cells pre-treated with L.rhamnosus.Pre-treatment with L.rhamnosus counteracted F4+ ETEC-induced increases in TNF-αconcentration.Increased PGE2.concentrations were observed in cells infected with F4+ ETEC and in cells treated with L.rhamnosus only.A decrease in phosphorylated epidermal growth factor receptor(EGFR) was observed at 3 h after F4+ ETEC challenge in cells treated with L.rhamnosus.Pre-treatment with L.rhamnosus enhanced Akt phosphorylation and increased ZO-1 and occludin protein expression.Our findings suggest that L.rhamnosus protects intestinal epithelial cells from F4+ ETEC-induced damage,partly through the anti-inflammatory response involving synergism between TLR2 and NODI.In addition,L.rhamnosus promotes EGFR-independent Akt activation,which may activate intestinal epithelial cells in response to bacterial infection,in turn increasing tight junction integrity and thus enhancing the barrier function and restricting pathogen invasion.Pre-incubation with L.rhamnosus was superior to co-incubation in reducing the adhesion of F4+ ETEC to IPEC-J2 cells and subsequently attenuating F4+ ETEC-induced mucin layer destruction and suppressing apoptosis.Our data indicate that a selected L.rhamnosus strain interacts with porcine intestinal epithelial cells to maintain the epithelial barrier and promote intestinal epithelial cell activation in response to bacterial infection,thus protecting cells from the deleterio