Bacteria-induced ROS generation greatly influences eukaryotic signaling pathways including those inducing Nrf2 [6, 7], and improved Nrf2-mediated protection is associated with beneficial effects elicited by probiotic intake [8, 9]. When studying host responses, there is a tendency to focus on individual cell types that comprise the biological H 89 barriers to microorganisms to obtain information on a particular cellular reaction to a microbe. Specifically, in vitro studies have focused on interactions between

probiotics and enterocytes. The immunomodulatory role of the intestinal epithelium is attracting considerable attention, in addition to its well-known role in barrier function. In analyses of enterocytes, it was shown that Bifidobacterium infantis and Lactobacillus salivarius did not induce proinflammatory responses in human intestinal epithelial cells (IECs) compared IAP inhibitor with the responses generated by Salmonella typhimurium, suggesting that IECs display immunological unresponsiveness when exposed to LAB [10]. Using a co-culture model including Caco-2 (IEC) and PBMC cells, Haller et al. also observed differential IEC activations

between Escherichia coli and LAB strains [11]. Furthermore, Rimoldi et al. reported that the release of pro-inflammatory mediators by IECs in response to bacteria Histone demethylase is dependent on bacterial invasiveness and the presence of flagella in a human

co-culture system [12]. Other relevant studies have focused on dendritic cells (DCs), canonical antigen-presenting cells, that can effectively induce primary immune responses against microbial infections and other stimuli [13, 14]. A recent report demonstrated that individual strains from the Lactobacillus group can differentially regulate the expression of surface markers and cytokine production by DCs [15]. By using human DCs as a model, it was shown that bacterial strains belonging to different species display distinct immunomodulatory effects [16]. Moreover, different strains of the same species can also differentially polarize the immune response [17, 18]. Recently, we have examined this aspect by focusing on L. paracasei that we have found to induce the highest maturation degree of DCs among the tested species [19]. In particular, we observed a differential ability of five genetically characterized L. paracasei strains to modulate DCs [20]. In this study, we addressed the same question by studying L. gasseri. We focused on L. gasseri because this species induces relevant immune activities in human patients [21].