Modulation of Human DCs by a Lactobacillus Strain Figure 5. Expression levels of TLR signalling pathway in DCs treated with L. paracasei, Salmonella or both. Comparison of the expression of TLR9, MYD88, IRAK-1, IRAK-4 and TOLLIP in DCs in the presence of the probiotic (Prob), its supernatant (CFS), Salmonella (S.typhi) or a combination. LPS, 20 ng/ml, was used as a positive control. The fold change (Fc) represents the ratio of the expression in treated DCs to the expression in control cells. The data shown are the mean values and SEM of three independent experiments. *p,0.05 compared to controls; #p,0.05 compared to S.typhi. doi:10.1371/journal.pone.0043197.g005 This TLR recognises peptidoglycan, the main component of Gram-positive bacteria, as Lactobacillus. A similar effect has been described by other authors for L. plantarum BFE 1685 and L. rhamnosus GG, which increase the expression of TLR2 in human epithelial cells [38] and L. casei CRL 431 in mice [36]. Recently, it has been reported that this TLR plays a key role in the stimulation of DCs and macrophages in the presence of bacteria from the genus Lactobacillus [39]. In line with several studies, our results suggest that probiotic bacteria increase the expression of TLR2 and TLR9, activating innate immunity [38,40–42]. Furthermore, TLR2 stimulation also appears to enhance the epithelial barrier, and it has been shown that the activation of this TLR plays an essential role in resistance to bacterial invasion [43]. TLR4 expression was decreased in response of the probiotic and Salmonella stimulation. Recently, Villena et al. reported that L.jensenii TL2937 attenuates the inflammatory response triggered by the activation of this TLR in porcine intestinal epithelial cells PLOS ONE | www.plosone.org 7 August 2012 | Volume 7 | Issue 8 | e43197