Background: Lactobacilli show anti-inflammatory effects in the human intestine, and their genomic DNA was identified as one of the anti-inflammatory components. Increased levels of the natural protease inhibitor elafin in the intestine plays an important role in protection against intestinal inflammation. However, there have been no previous reports regarding whether lactobacilli increase elafin levels.
Objective: This study was performed to investigate whether Lactobacillus plantarum induces elafin secretion from the human epithelial colorectal adenocarcinoma cell line, Caco-2. Moreover, we examined the roles of bacterial genomic DNA and toll-like receptor 9 (TLR9), a specific receptor of bacterial DNA, in this effect.
Methods: Elafin secretion from Caco-2 cells by live and heat-killed L. plantarum was measured. The analysis was also performed using DNase-treated L. plantarum and genomic DNA extracted from L. plantarum. We examined the role of TLR9 in elafin secretion by L. plantarum and its genomic DNA by suppressing TLR9 expression using RNAi in Caco-2 cells.
Results: Heat-killed L. plantarum time- and dose-dependently increased elafin secretion, whereas live L. plantarum had no such effect. The elafin secretion by heat-killed L. plantarum was partially abolished by DNase treatment of the bacterium. In addition, L. plantarum genomic DNA also increased elafin secretion. Furthermore, suppression of TLR9 expression partially or completely abolished elafin secretion by heat-killed L. plantarum and its genomic DNA.
Conclusion: Our results indicated that heat-killed L. plantarum induced genomic DNA-dependent and TLR9-mediated elafin secretion. The anti-inflammatory effects of lactobacilli may be mediated by increases in the levels of elafin in the intestine.