Dendritic cells (DCs), the most potent antigen-presenting cells, are commanders-in-chief of the immune namely system, determining the nature and type of immune responses [2]. Intestinal DCs are central in controlling immune tolerance in the gastrointestinal tract [3]�C[5]. DCs also imprint homing markers on T-cells that they stimulate e.g. gut DCs induce gut-homing markers on T-cells, localizing immune responses to specific tissues [6]. Regulatory cytokine IL-10 is essential in preventing inflammatory and autoimmune pathologies and is crucial for maintenance of intestinal homeostasis [7], [8]. The intestinal microbiota interacts with the local immune system promoting the mechanisms of intestinal homeostasis in health [9]�C[11].

In certain disorders such as inflammatory bowel disease (IBD), this homeostasis is disrupted leading to a deregulated immune activity in the gut [12]. Harnessing the contribution of pro- and/or prebiotics to gut homeostasis has been proposed as alternative or complementary treatment for patients with IBD [13]. Direct exposure of DCs in vitro to different commensal bacteria has variable effects on DC phenotype and function often promoting anti-inflammatory activity [4], implying immunomodulation by commensal bacteria acts via DC in vivo [14]. However, the molecular mechanisms through which commensal bacteria interact with the human host and exert such immunomodulatory properties have remained elusive. Extracellular proteins of bacteria are currently being characterised as potential mediators between commensal bacteria and the human host [15].

Such proteins could have relevant roles mediating interaction with the local microenvironment, including communication with other bacteria and the host immune system and even modulating the maintenance of the mucosal barrier [16]. We hypothesize therefore that the dialogue between intestinal bacteria and DC is partially mediated by the secretion of soluble bacterial compounds (including proteins). To that end, we used a model of Lactobacillus plantarum and human DCs. L. plantarum is a lactic-acid-producing bacterium (LAB) with the largest genome [17] within the genus. This size provides the species with a high versatility to bind to different surfaces, and a great capacity for adaptation to diverse environmental conditions [18]. L. plantarum can be found in a wide array of fermented foods in different geographical regions [19] and, in addition, some L. plantarum strains, such as 299 v or WCFS1, confer benefits on human health, thus being considered Brefeldin_A as probiotics [20], [21]. Noteworthy, L. plantarum modulates the gene expression profile of the human intestine in vivo, promoting mechanisms of immune tolerance [22]. In addition, there is some evidence of L.