Lactobacillus casei ATCC 393 alleviates Enterotoxigenic Escherichia coli K88-induced intestinal barrier dysfunction via TLRs/mast cells pathway

Mast cells play a crucial role in gastrointestinal physiology and pathophysiology. This study was conducted to investigate the role of mast cells (MCs) in the protective effect of Lactobacillus casei ATCC 393 (L. casei ATCC 393) on intestinal barrier function. The regulatory effect of L. casei ATCC 393 on intestinal barrier dysfunction and MCs activation induced by Enterotoxigenic Escherichia coli K88 (ETEC K88) were evaluated by porcine mucosal mast cells (PMMCs)-porcine jejunal epithelial cells (IPEC-J2)-L. casei ATCC 393 co-culture experiments in vitro and MCs stabilizer drug experiment in vivo. Results showed that L. casei ATCC 393 pretreatment effectively alleviated the reduction of cell viability and increase of permeability in ETEC K88-infected IPEC-J2 cells. L. casei ATCC 393 pretreatment inhibited the increase of proinflammatory cytokines and some other MCs mediators, and decrease of anti-inflammatory cytokines in ETEC K88-infected PMMCs. Cromolyn sodium or L. casei ATCC 393 prevented ETEC K88-induced increase of intestinal epithelial cell permeability in IPEC-J2 cells when co-cultivation with PMMCs. Furthermore, cromolyn sodium or L. casei ATCC 393 pretreatment attenuated ETEC K88-induced increase of MCs mediators, mast cell proteases (MCPs) and carboxypeptidase A3 (CPA3) mRNA levels, and down-regulation of tight junction proteins, Toll-like receptor 2 and 4 (TLR2 and TLR4) expression levels in mice challenged by ETEC K88. These results indicated that intestinal barrier dysfunction caused by ETEC K88 was mediated by intestinal mast cell activation which can be prevented by L. casei ATCC 393 via TLRs signaling pathway.