Effects of Lactobacillus rhamnosus GG on the maturation and differentiation of dendritic cells in rotavirus-infected mice

Rotavirus-related diarrhoea is considered one of the most important diseases in field animal production. In addition to the classic vaccine strategy, a number of studies have utilised probiotics, such as Lactobacillus rhamnosus GG (LGG), to prevent rotavirus-induced diarrhoea. Although it has been partially revealed that Toll-like receptors (TLRs) are involved in the LGG-mediated protection against rotavirus infection, the details of the underlying immunologic mechanisms remain largely unknown. In this study, three-to-four-week-old female BALB/c mice were divided into three groups and orally administered phosphate buffered saline (PBS), PBS plus rotavirus or LGG plus rotavirus, respectively. The differentiation and maturation of dendritic cells (DCs) were then determined by FACS, the expression levels of TLR-3 and nuclear factor kappa beta (NF-κB) were evaluated using real time PCR, and the production of inflammatory cytokines in mesenteric lymph nodes (MLNs) were determined by ELISA. The results demonstrated that rotavirus infection significantly increased the percentage of CD11c⁺CD11b⁺CD8a^- DCs and decreased the percentage of CD11c⁺CD11b^-CD8a⁺ DCs in MLNs. By contrast, the presence of LGG significantly decreased the percentage of CD11c⁺CD11b⁺CD8a^- DCs and increased the percentage of CD11c⁺CD11b^-CD8a⁺ DCs, which indicates that the differentiation of DCs is involved in the protective effects of LGG. Rotavirus infection also resulted in the increased expression of surface markers such as CD40, CD80 and MHC-II in DCs, and the administration of LGG significantly increased the expression level further. The mRNA levels of TLR-3 and NF-κB in the intestine and MLNs were also significantly increased in the presence of rotavirus, which was further increased in the presence of LGG. The production of inflammatory cytokines was also determined, and the results showed that rotavirus caused the increased production of interleukin (IL)-12 and tumour necrosis factor alpha; this effect was further enhanced by LGG. Meanwhile, although rotavirus infection led to the increased production of IL-6 and IL-10, the presence of LGG significantly decreased the mRNA levels of these cytokines. By contrast, rotavirus infection resulted in the decreased production of interferon gamma (IFN-γ), and the administration of LGG significantly increased the levels of IFN-γ. Taken together, the protective effects of LGG were partially due to the modulation of the differentiation and maturation of DCs, the increased production of TLR-3 and NF-κB, and the modulation of inflammatory cytokines.

Regulation of lung immunity and host defense by the intestinal microbiota

Every year in the United States approximately 200,000 people die from pulmonary infections, such as influenza and pneumonia, or from lung disease that is exacerbated by pulmonary infection. In addition, respiratory diseases such as, asthma, affect 300 million people worldwide. Therefore, understanding the mechanistic basis for host defense against infection and regulation of immune processes involved in asthma are crucial for the development of novel therapeutic strategies. The identification, characterization, and manipulation of immune regulatory networks in the lung represents one of the biggest challenges in treatment of lung associated disease. Recent evidence suggests that the gastrointestinal (GI) microbiota plays a key role in immune adaptation and initiation in the GI tract as well as at other distal mucosal sites, such as the lung. This review explores the current research describing the role of the GI microbiota in the regulation of pulmonary immune responses. Specific focus is given to understanding how intestinal “dysbiosis” affects lung health.

Lactobacillus paracasei CNCM I-4034 and its culture supernatant modulate Salmonella-induced inflammation in a novel transwell co-culture of human intestinal-like dendritic and Caco-2 cells

Background

The action of probiotics has been studied in vitro in cells isolated from both mice and humans, particularly enterocytes (IECs), dendritic cells (DCs) and co-cultures of peripheral DCs and IECs. Peripheral DCs and murine DCs differ from human gut DCs, and to date there are no data on the action of any probiotic on co-cultured human IECs and human intestinal DCs. To address this issue, a novel transwell model was used. Human IECs (Caco-2 cells) grown in the upper chamber of transwell filters were co-cultured with intestinal-like human DCs grown in the basolateral compartment of the transwells. The system was apically exposed for 4 h to live probiotic L. paracasei CNCM I-4034 obtained from the faeces of breastfed infants or to its cell-free culture supernatant (CFS) and challenged with Salmonella typhi. The secretion of pro- and anti-inflammatory cytokines in the basolateral compartment was determined by immunoassay, and the DC expression pattern of 20 TLR signaling pathway genes was analysed by PCR array.

Results

The presence of the live probiotic alone significantly increased IL-1β, IL-6, IL-8, TGF-β2, RANTES and IP-10 levels and decreased IL-12p40, IL-10, TGF- β1 and MIP-1α levels. This release was correlated with a significant increase in the expression of almost all TLR signaling genes. By contrast, incubation of the co-culture with CFS increased IL-1β, IL-6, TGF-β2 and IP-10 production only when Salmonella was present. This induction was correlated with an overall decrease in the expression of all TLR genes except TLR9, which was strongly up-regulated.

Conclusions

The data presented here clearly indicate that L. paracasei CNCM I-4034 significantly increases the release of pro-inflammatory cytokines, enhances TLR signaling pathway activation and stimulates rather than suppresses the innate immune system. Furthermore, our findings provide evidence that the effects of probiotics in the presence of IECs and DCs differ from the effects of probiotics on cultures of each cell type alone, as reported by us earlier. Thus, co-culture systems such as the one described here are needed to characterise the effects of probiotics in vitro, highlighting the potential utility of such co-cultures as a model system.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-015-0408-6) contains supplementary material, which is available to authorized users.

Proteinase PrtP impairs lactococcin LcnB activity in Lactococcus lactis BGMN1-501: new insights into bacteriocin regulation

Proteinases and bacteriocins are of great importance to the dairy industry, but their interactions have not been studied so far. Lactococcus lactis subsp. lactis BGMN1-5 is a natural isolate from homemade semi-hard cheese which produces two bacteriocins (Lactococcin B and LsbB), as well as proteinase PrtP. A medium-dependent increase in the bacteriocin LcnB activity of L. lactis BGMN1-501, a derivate of L. lactis subsp. lactis BGMN1-5, was shown to be accompanied by a decrease in its promoter activity. A similar effect of media components on gene expression was reported for proteinase PrtP, whose gene is co-localized on the same plasmid as the lcnB gene. Thus, the PrtP-LcnB interplay was investigated. Single gene knockout mutants were constructed with disrupted prtP or lcnB genes. PrtP(-) mutants showed higher bacteriocin activity that had lost its growth medium dependence, which was in contrast to the original strain. When LcnB from this mutant was combined with proteinase from the LcnB(-) mutant in vitro, its activity was rendered to the original level, suggesting that proteinase reduces bacteriocin activity. We propose a new model of medium dependent expression of these genes with regard to the effects of their interaction in vivo.

Lactobacillus rhamnosus and its cell-free culture supernatant differentially modulate inflammatory biomarkers in Escherichia coli-challenged human dendritic cells

The intestinal immune system maintains a delicate balance between immunogenicity against invading pathogens and tolerance to the commensal microbiota and food antigens. Different strains of probiotics possess the ability to finely regulate the activation of dendritic cells (DC), polarising the subsequent activity of T-cells. Nevertheless, information about their underlying mechanisms of action is scarce. In the present study, we investigated the immunomodulatory effects of a potentially probiotic strain, Lactobacillus rhamnosus CNCM I-4036, and its cell-free culture supernatant (CFS) on human DC challenged with Escherichia coli. The results showed that the levels of pro-inflammatory cytokines such as IL-1β, IL-6, IL-8 and IL-12p70 were higher in the cells treated with live L. rhamnosus than in the cells treated with the CFS. In the presence of E. coli, the supernatant was more effective than the probiotic bacteria in reducing the secretion of pro-inflammatory cytokines. In addition, live L. rhamnosus potently induced the production of transforming growth factor (TGF)-β1 and TGF-β2, whereas the CFS increased the secretion of TGF-β1. However, in the presence of E. coli, both treatments restored the levels of TGF-β. The probiotic strain L. rhamnosus CNCM I-4036 and its CFS were able to activate the Toll-like receptor signalling pathway, enhancing innate immunity. The two treatments induced gene transcription of TLR-9. Live L. rhamnosus activated the expression of TLR-2 and TLR-4 genes, whereas the CFS increased the expression of TLR-1 and TLR-5 genes. In response to the stimulation with probiotic/CFS and E. coli, the expression of each gene tested was notably increased, with the exception of TNF-α and NFKBIA. In conclusion, the CFS exhibited an extraordinary ability to suppress the production of pro-inflammatory cytokines by DC, and may be used as an effective and safer alternative to live bacteria.

Interaction with intestinal epithelial cells promotes an immunosuppressive phenotype in Lactobacillus casei

Maintenance of the immunological tolerance and homeostasis in the gut is associated with the composition of the intestinal microbiota. We here report that cultivation of Lactobacillus casei ATCC 334 in the presence of human intestinal epithelial cells promotes functional changes in bacteria. In particular, the interaction enhanced the immunosuppressive phenotype of L. casei as demonstrated by the ability of L. casei to generate functional regulatory T cells (CD4+CD25+FoxP3+) and production of the anti-inflammatory cytokine interleukin-10 by human peripheral blood mononuclear cells. The results indicate microbe-host cross-talk that changes features of microbes, and suggest that in vitro simulation of epithelial cell interaction can reveal functional properties of gut microbes more accurately than conventional cultivation.

Probiotic modulation of dendritic cell function is influenced by ageing

Dendritic cells (DCs) are critical for the generation of T-cell responses. DC function may be modulated by probiotics, which confer health benefits in immunocompromised individuals, such as the elderly. This study investigated the effects of four probiotics, Bifidobacterium longum bv. infantis CCUG 52486, B. longum SP 07/3, Lactobacillus rhamnosus GG (L.GG) and L. casei Shirota (LcS), on DC function in an allogeneic mixed leucocyte reaction (MLR) model, using DCs and T-cells from young and older donors in different combinations. All four probiotics enhanced expression of CD40, CD80 and CCR7 on both young and older DCs, but enhanced cytokine production (TGF-β, TNF-α) by old DCs only. LcS induced IL-12 and IFNγ production by DC to a greater degree than other strains, while B. longum bv. infantis CCUG 52486 favoured IL-10 production. Stimulation of young T cells in an allogeneic MLR with DC was enhanced by probiotic pretreatment of old DCs, which demonstrated greater activation (CD25) than untreated controls. However, pretreatment of young or old DCs with LPS or probiotics failed to enhance the proliferation of T-cells derived from older donors. In conclusion, this study demonstrates that ageing increases the responsiveness of DCs to probiotics, but this is not sufficient to overcome the impact of immunosenescence in the MLR.

TLR2 & Co: a critical analysis of the complex interactions between TLR2 and coreceptors

TLRs play a major role in microbe-host interactions and innate immunity. Of the 10 functional TLRs described in humans, TLR2 is unique in its requirement to form heterodimers with TLR1 or TLR6 for the initiation of signaling and cellular activation. The ligand specificity of TLR2 heterodimers has been studied extensively, using specific bacterial and synthetic lipoproteins to gain insight into the structure-function relationship, the minimal active motifs, and the critical dependence on TLR1 or TLR6 for activation. Different from that for specific well-defined TLR2 agonists, recognition of more complex ligands like intact microbes or molecules from endogenous origin requires TLR2 to interact with additional coreceptors. A breadth of data has been published on ligand-induced interactions of TLR2 with additional pattern recognition receptors such as CD14, scavenger receptors, integrins, and a range of other receptors, all of them important factors in TLR2 function. This review summarizes the roles of TLR2 in vivo and in specific immune cell types and integrates this information with a detailed review of our current understanding of the roles of specific coreceptors and ligands in regulating TLR2 functions. Understanding how these processes affect intracellular signaling and drive functional immune responses will lead to a better understanding of host-microbe interactions and will aid in the design of new agents to target TLR2 function in health and disease.

Divergent immunomodulating effects of probiotics on T cell responses to oral attenuated human rotavirus vaccine and virulent human rotavirus infection in a neonatal gnotobiotic piglet disease model

Rotaviruses (RVs) are a leading cause of childhood diarrhea. Current oral vaccines are not effective in impoverished countries where the vaccine is needed most. Therefore, alternative affordable strategies are urgently needed. Probiotics can alleviate diarrhea in children and enhance specific systemic and mucosal Ab responses, but the T cell responses are undefined. In this study, we elucidated the T cell and cytokine responses to attenuated human RV (AttHRV) and virulent human RV (HRV) in gnotobiotic pigs colonized with probiotics (Lactobacillus rhamnosus strain GG [LGG] and Bifidobacterium lactis Bb12 [Bb12]), mimicking gut commensals in breastfed infants. Neonatal gnotobiotic pigs are the only animal model susceptible to HRV diarrhea. Probiotic colonized and nonvaccinated (Probiotic) pigs had lower diarrhea and reduced virus shedding postchallenge compared with noncolonized and nonvaccinated pigs (Control). Higher protection in the Probiotic group coincided with higher ileal T regulatory cells (Tregs) before and after challenge, and higher serum TGF-β and lower serum and biliary proinflammatory cytokines postchallenge. Probiotic colonization in vaccinated pigs enhanced innate serum IFN-α, splenic and circulatory IFN-γ-producing T cells, and serum Th1 cytokines, but reduced serum Th2 cytokines compared with noncolonized vaccinated pigs (Vac). Thus, LGG+Bb12 induced systemic Th1 immunostimulatory effects on oral AttHRV vaccine that coincided with lower diarrhea severity and reduced virus shedding postchallenge in Vac+Pro compared with Vac pigs. Previously unreported intestinal CD8 Tregs were induced in vaccinated groups postchallenge. Thus, probiotics LGG+Bb12 exert divergent immunomodulating effects, with enhanced Th1 responses to oral AttHRV vaccine, whereas inducing Treg responses to virulent HRV.

Lactobacillus casei Zhang modulate cytokine and toll-like receptor expression and beneficially regulate poly I:C-induced immune responses in RAW264.7 macrophages

Lactobacilli are frequently used as probiotics due to their beneficial effects on health. Lactobacillus casei Zhang (LcZ), which has favorable probiotic properties, was first isolated from koumiss. In this study, the immunomodulating effects of LcZ on cytokine and toll-like receptor expression in RAW264.7 macrophages was assessed and it was found that live LcZ promotes production of nitric oxide (NO), tumor necrosis factor (TNF)-α, interleukin (IL)-6 and interferon (IFN)-β. Transcription of inducible nitric oxide synthase (iNOS) was also enhanced by viable LcZ. The immunostimulating effects of live LcZ are significantly attenuated in heat-killed LcZ. Live LcZ promotes TLR2 mRNA transcription, whereas heat-killed LcZ enhances transcription of TLR2, TLR3, TLR4 and TLR9. Furthermore, live LcZ significantly suppresses polyinosinic:polycytidylic acid (poly I:C)-stimulated NO, iNOS and TNF-α expression while enhancing expression of IFN-β. It was also found that poly I:C-induced interferon regulatory factor 3 (IRF-3) reporter gene activity was significantly up-regulated by live LcZ. These results suggest that LcZ keeps the innate immune system alert by increasing transcription of Toll-like receptors and enhancing production of pro-inflammatory mediators and type I IFN in macrophages. The synergistic effect of live LcZ with poly I:C on IFN-β expression is associated with increased activity of IRF-3. LcZ has the potential to be used as an adjuvant against viral infections.

Challenges in translational research on probiotic lactobacilli: from in vitro assays to clinical trials

Beneficial effects of certain probiotic strains have been established in the treatment and prevention of various immune and intestinal disorders in humans, including allergic diseases, chronic inflammatory diseases and diarrhoea. The proposed mechanisms underlying the immunomodulatory effects of probiotics in humans are not understood in precise detail but include enhancement of intestinal barrier function, altered epithelial signalling, competition with pathogens and effects on immune cells and immunity depending on the probiotic strain. The publication of controversial or inconclusive probiotic studies in humans highlights the need for a better understanding of the mechanisms and improved strain selection criteria. This review focuses on the immunomodulatory properties of lactobacilli and bifidobacteria in vitro and in vivo, current knowledge concerning the mechanisms in vivo and challenges in translational research on probiotics. A better understanding of the molecular mechanisms of probiotics, the effect of probiotic mixtures versus single strains, the effect of formulation of probiotics and the fate of ingested probiotics should help to clarify the value of immune assays as selection criteria for probiotics.

Dietary heme alters microbiota and mucosa of mouse colon without functional changes in host-microbe cross-talk

Colon cancer is a major cause of cancer deaths in Western countries and is associated with diets high in red meat. Heme, the iron-porphyrin pigment of red meat, induces cytotoxicity of gut contents which injures surface cells leading to compensatory hyperproliferation of crypt cells. This hyperproliferation results in epithelial hyperplasia which increases the risk of colon cancer. In humans, a high red-meat diet increases Bacteroides spp in feces. Therefore, we simultaneously investigated the effects of dietary heme on colonic microbiota and on the host mucosa of mice. Whole genome microarrays showed that heme injured the colonic surface epithelium and induced hyperproliferation by changing the surface to crypt signaling. Using 16S rRNA phylogenetic microarrays, we investigated whether bacteria play a role in this changed signaling. Heme increased Bacteroidetes and decreased Firmicutes in colonic contents. This shift was most likely caused by a selective susceptibility of Gram-positive bacteria to heme cytotoxic fecal water, which is not observed for Gram-negative bacteria, allowing expansion of the Gram-negative community. The increased amount of Gram-negative bacteria most probably increased LPS exposure to colonocytes, however, there is no appreciable immune response detected in the heme-fed mice. There was no functional change in the sensing of the bacteria by the mucosa, as changes in inflammation pathways and Toll- like receptor signaling were not detected. This unaltered host-microbe cross-talk indicates that the changes in microbiota did not play a causal role in the observed hyperproliferation and hyperplasia.

Induced apoptosis of Th2 lymphocytes and inhibition of airway hyperresponsiveness and inflammation by combined lactic acid bacteria treatment

Several lactic acid bacteria (LAB) demonstrably regulate the immune system and inhibit allergic disease. This study examined whether oral feeding of either Lactobacillus paracasei (L. paracasei) BB5 and/or Lactobacillus rhamnosus (L. rhamnosus) BB1 suppresses ovalbumin (OVA)-induced airway hyperresponsiveness (AHR) and inflammation in a murine model. OVA-specific immune responses, cell profile of bronchoalveolar lavage fluid (BALF), and airway AHR were assessed following OVA and methacholine challenge. We investigated whether LAB can enhance CD4(+)FoxP3(+) and CD8(+)FoxP3(+) regulatory T (Treg) cells in splenic cells and apoptosis of CD4(+)IL-4(+) T cells. Results found oral administration of combined LAB better than single L. paracasei or L. rhamnosus strain, improving Penh ratio after challenge with methacholine. High-dose combined LAB starkly decreased synthesis of OVA-specific IgE and IgG2a levels, as well as eosinophils infiltration in BALF. In addition, CD4(+)IL-4(+) T cells decreased while CD4(+)FoxP3(+) and CD8(+)FoxP3(+) Treg cells increased significantly in splenic mononuclear cells of high-dose combined LAB group. Findings indicate allergen-induced AHR and airway allergic inflammation suppressed by enhances CD4(+)FoxP3(+) and CD8(+)FoxP3(+) Treg populations as well as Th1 cell response after treating with combined LAB. This study may provide a basis for developing a novel therapeutic or protective method for airway allergic disease.

Human intestinal dendritic cells decrease cytokine release against Salmonella infection in the presence of Lactobacillus paracasei upon TLR activation

Probiotic bacteria have been shown to modulate immune responses and could have therapeutic effects in allergic and inflammatory disorders. However, little is known about the signalling pathways that are engaged by probiotics. Dendritic cells (DCs) are antigen-presenting cells that are involved in immunity and tolerance. Monocyte-derived dendritic cells (MoDCs) and murine DCs are different from human gut DCs; therefore, in this study, we used human DCs generated from CD34+ progenitor cells (hematopoietic stem cells) harvested from umbilical cord blood; those DCs exhibited surface antigens of dendritic Langerhans cells, similar to the lamina propria DCs in the gut. We report that both a novel probiotic strain isolated from faeces of exclusively breast-fed newborn infants, Lactobacillus paracasei CNCM I-4034, and its cell-free culture supernatant (CFS) decreased pro-inflammatory cytokines and chemokines in human intestinal DCs challenged with Salmonella. Interestingly, the supernatant was as effective as the bacteria in reducing pro-inflammatory cytokine expression. In contrast, the bacterium was a potent inducer of TGF-β2 secretion, whereas the supernatant increased the secretion of TGF-β1 in response to Salmonella. We also showed that both the bacteria and its supernatant enhanced innate immunity through the activation of Toll-like receptor (TLR) signalling. These treatments strongly induced the transcription of the TLR9 gene. In addition, upregulation of the CASP8 and TOLLIP genes was observed. This work demonstrates that L. paracasei CNCM I-4034 enhanced innate immune responses, as evidenced by the activation of TLR signalling and the downregulation of a broad array of pro-inflammatory cytokines. The use of supernatants like the one described in this paper could be an effective and safe alternative to using live bacteria in functional foods.

Immunomodulatory effects of potential probiotics in a mouse peanut sensitization model

Peanut allergy accounts for the majority of severe food-related allergic reactions and there is a need for new prevention and treatment strategies. Probiotics may be considered for treatment on the basis of their immunomodulating properties. Cytokine profiles of probiotic strains were determined by in vitro co-culture with human PBMCs. Three strains were selected to investigate their prophylactic potential in a peanut sensitization model by analysing peanut-specific antibodies, mast cell degranulation and ex vivo cytokine production by splenocytes. The probiotic strains induced highly variable cytokine profiles in PBMCs. L. salivarius HMI001, L. casei Shirota (LCS) and L. plantarum WCFS1 were selected for further investigation owing to their distinct cytokine patterns. Prophylactic treatment with both HMI001 and LCS attenuated the Th2 phenotype (reduced mast cell responses and ex vivo IL-4 and/or IL-5 production). In contrast, WCFS1 augmented the Th2 phenotype (increased mast cell and antibody responses and ex vivo IL-4 production). In vitro PBMC screening was useful in selecting strains with anti-inflammatory and Th1 skewing properties. In case of HMI001 (high IL-10/IL-12 ratio) and LCS (high interferon-γ and IL-12), partial protection was seen in a mouse peanut allergy model. Strikingly, certain strains may worsen the allergic reaction as shown in the case of WCFS1.

Immunomodulatory effects of Streptococcus suis capsule type on human dendritic cell responses, phagocytosis and intracellular survival

Streptococcus suis is a major porcine pathogen of significant commercial importance worldwide and an emerging zoonotic pathogen of humans. Given the important sentinel role of mucosal dendritic cells and their importance in induction of T cell responses we investigated the effect of different S. suis serotype strains and an isogenic capsule mutant of serotype 2 on the maturation, activation and expression of IL-10, IL-12p70 and TNF-α in human monocyte-derived dendritic cells. Additionally, we compared phagocytosis levels and bacterial survival after internalization. The capsule of serotype 2, the most common serotype associated with infection in humans and pigs, was highly anti-phagocytic and modulated the IL-10/IL-12 and IL-10/TNF-α cytokine production in favor of a more anti-inflammatory profile compared to other serotypes. This may have consequences for the induction of effective immunity to S. suis serotype 2 in humans. A shielding effect of the capsule on innate Toll-like receptor signaling was also demonstrated. Furthermore, we showed that 24 h after phagocytosis, significant numbers of viable intracellular S. suis were still present intracellularly. This may contribute to the dissemination of S. suis in the body.

Immunomodulatory mechanisms of lactobacilli

Over the past decade it has become clear that lactobacilli and other probiotic and commensal organisms can interact with mucosal immune cells or epithelial cells lining the mucosa to modulate specific functions of the mucosal immune system. The most well understood signalling mechanisms involve the innate pattern recognition receptors such as Toll-like receptors, nucleotide oligomerization domain-like receptors and C-type lectin receptors. Binding of microbe-associated molecular patterns with these receptors can activate antigen presenting cells and modulate their function through the expression of surface receptors, secreted cytokines and chemokines. In vitro the cytokine response of human peripheral blood mononuclear cells and dendritic cells to lactobacilli can be strikingly different depending on both the bacterial species and the strain. Several factors have been identified in lactobacilli that influence the immune response in vitro and in vivo including cell surface carbohydrates, enzymes modifying the structure of lipoteichoic acids and metabolites. In mice mechanistic studies point to a role for the homeostatic control of inducible T regulatory cells in the mucosal tissues as one possible immunomodulatory mechanism. Increasing evidence also suggests that induction of epithelial signalling by intestinal lactobacilli can modulate barrier functions, defensin production and regulate inflammatory signalling. Other probiotic mechanisms include modulation of the T cell effector subsets, enhancement of humoral immunity and interactions with the epithelial-associated dendritic cells and macrophages. A major challenge for the future will be to gain more knowledge about the interactions occurring between lactobacilli and the host in vivo and to understand the molecular basis of innate signalling in response to whole bacteria which trigger multiple signalling pathways.