LAUSR

Lactobacillus zeae (LB1) has been shown to prevent Caenorhabditis elegans from death caused by enterotoxigenic Escherichia coli (ETEC) infection through downregulating the gene expression of ETEC toxins and mediating antimicrobial peptides/defense molecules under the p38 MAPK and DAF/IGF signaling pathways in the nematode. However, the protective effects of LB1 at a cellular level have not been investigated yet. In the present study, porcine intestinal cells (IPEC-J2) were used to examine the potential of LB1 on modulating intestinal barrier and innate immune functions and protecting against intestinal injuries and inflammatory reactions induced by ETEC F4 infection. The results showed that the pretreatment of IPEC-J2 cells with LB1 significantly alleviated the cytotoxicity and inhibited gene expression of interleukin (IL)-8 and IL-6, and secretion of IL-8 induced by ETEC F4 (P < 0.05). The LB1 pretreatment significantly maintained a higher value of TEER concomitantly with lower dextran-fluorescein fluxes from the apical side to the basolateral side when compared with that challenged by ETEC F4. LB1 pretreatment also prevented morphological damage of tight junction and cytoskeleton caused by the ETEC F4 challenge, indicating that LB1 pretreatment maintained the structural integrity of tight junction. However, LB1 inclusion showed no significant protection on ZO-1 expression at both gene and protein levels from the ETEC F4 challenge, but a considerable increase in the protein expression of occludin (P < 0.05). LB1 administration influenced neither ETEC F4 adhesion nor secretion of antimicrobial defensin (pBD2, pBD3), while dramatically reduced the mRNA level of toll-like receptor 4 (TLR4). These results suggested that probiotics LB1 could effectively protect the mucosa from ETEC F4 infection by inhibiting inflammation and maintaining barrier integrity via downregulating TLR4 expression. Our data provide further evidence on the mechanisms at the cellular level that probiotics could improve pig gut health.