In vitro evaluation of Lactobacillus plantarum DSMZ 12028 as a probiotic: emphasis on innate immunity.

In this study, we analyzed the probiotic potential of L. plantarum DSMZ 12028 in vitro using the pathogen E. coli K4 and a certified probiotic, L. paracasei F19, as controls. Adhesion to intestinal epithelial cells was evaluated using two cell lines, CaCo-2 and HT-29, through the plate dilution method. Moreover, the bacteria/epithelial dynamic interaction was continuously monitored using time-lapse microscopy. Expression of the innate immunity receptors, the TLRs, was evaluated by semi-quantitative PCR on an epithelial/bacteria co-culture. Real-time PCR was used to monitor expression of TLRs and cytokines in a monocytic cell line (THP-1) following bacterial exposure. The adherence of the strain to intestinal epithelial cells was comparable to that of the probiotic. Time-lapse experiments showed that E. coli K4 induced cell death while L. plantarum did not affect proliferation at a 10:1 bacteria/cell ratio. L. plantarum down-regulated TLR mRNAs with the exception of TLR2, while L. paracasei F19 and E. coli K4 caused a significant (p<0.05) up-regulation of TLR2 and 4, respectively. To simulate the activation of underlying immune cells in the lamina propria, we analyzed the immunomodulation of L. plantarum on a monocytic cell line, THP-1. Proinflammatory cytokines, such as TNFalpha, were increased by the presence of bacteria. The pathogen E. coli K4 also induced a strong up-regulation of proinflammatory cytokines, such as IL8, IL1beta and IL23. No differences were observed between experimental groups for IFNgamma, IL-10 and IL12p40. Overall, L. plantarum DSMZ 12028 demonstrated probiotic traits, inducing a proinflammatory response just above the "threshold level", which could prevent an inflammatory outcome, while inducing a higher state of alertness in the defense system of the host intestinal epithelial cells.