L.Plantarum-Treated NK Cells Protect Intestinal Epithelial Cells from Barrier Disruption Caused By Enterotoxigenic Escherichia coli

Backgroung: Natural killing (NK) cells play a central role in host defense against pathogenic bacteria. Probiotics are able to modulate mucosal immune system in the intestine by maintaining intestinal homeostasis and tolerance towards resident microbiota. We previously found a strain of probiotics, Lactobacillus plantarum (L. plantarum), to significantly improve mucosal barrier integrity and function of the small intestine in a pig model. The present study is designed to investigate the anti-inflammatory potential of L. plantarum in NK cell-mediated intestinal epithelial barrier function under Escherichia coli (ETEC) K88 infection.

Methods: To study the effect of L. plantarum on the function of NK cells, a L. plantarum strain CGMCC1258 was cultured with NK-92MI cells without direct contact using a transwell system for 2 to 6 hours before collection of NK cells for mRNA and protein expression analysis. To study the anti-inflammatory potential of L. plantarum in NK cell-mediated epithelial cell integrity, NCM460 (an epithelial cell line) was exposed to ETEC K88 for 2 hours using transwell culturing system and subsequently stimulated in a cell-cell contact manner with NK-92MI cells pre-treated with L. plantarum for 4 hours.

Results: L. plantarum efficiently increased the protein and mRNA levels of NCRs, and the mRNA abundance of IL-10, perforin, INF-ɤ,TNF-α, IL-8 and IL-26. In addition, the protein levels of IL-10, LIF and IL-22 were increased by L.plantarum. Protein level of IL-22 was increased in the L.plantarum-treated NK cells supernatant. Transfer of L.plantarum-treated NK cells conferred protection against ETEC K88-induced intestinal epithelial barrier damages in NCM460 cells. Protection was associated with an increased expression of ZO-1 and occludin mRAN and protein in ETEC K88-infected NCM460 cells. Furthermore, adding L.plantarum-treated NK cells to ETEC K88-infected NCM460 cells, the protein and mRNA levels of IL-22R1 was increased in NCM460. L.plantarum-treated NK cells were also observed to induce an augmentation in protein levels of phosphorylated p38, JAK1, Stat3 and Tyk2 in ETEC K88-infected NCM460 cells.

Conclusion: L.plantarum-treated NK cells improved intestinal epithelial barrier function via IL-22-IL-22R pathway in NCM460 cells during ETEC-K88 infection.