Mulation at two years of age (Fig. 4A ). Similar trends were observed when analyzing colonization at one and two months of age for 
both IL-4 and IL-10 (data not shown).Co-colonization with lactobacilli dampens the S. aureus associated cytokine producing cell numbers at two years of ageAs early-life colonization with lactobacilli and S. aureus were associated with opposite pattern of cytokine-secreting cells at age two, we investigated early co-colonization with both, none or either of lactobacilli and S. aureus in relation to number of cytokinesecreting cells at age two after PHA stimulation. Infants were grouped according to their two-week colonization with lactobacilli and S. aureus, being colonized with both, one or none of the bacterial species (Fig. 3). From this grouping it was apparent that colonization with S. aureus in the absence of lactobacilli was associated with significantly elevated numbers of cytokine-secreting cells in comparison to the other colonization groups. Therefore, the children were re-grouped based on lactobacilli colonization at two weeks: infants colonized with S. aureus but notLactobacilli inhibits S. aureus induced T helper cell IFN-c production in FCCP manufacturer vitroGiven that colonization with S. aureus in the absence of lactobacilli was associated with significantly elevated numbers of cytokine-secreting cells, we aimed to 115103-85-0 further investigate the immunostimulatory capacity of these bacteria in vitro. Supernatants from L. rhamnosus GG (LGG) and S. aureus 161.2 were added to PBMCs and intracellular IL-42 and IFN-c production was analyzed with FACS. The release of these cytokines as well as IL10 was measured with ELISA. We found higher frequencies of IFN-c (p,0.01) and tendency towards increased IL-4 (p = 0.151) producing CD4+ T helper cells induced by S. aureus 161.2 supernatant than by LGG supernatant. When both supernatants were added simultaneously to the PBMC cultures, the frequencies of IFN-c2 (p,0.01) and IL-4 (p = 0.095) producing T helper cells were increased compared to LGG alone (Fig. 5 A ). Further, IFN-c release into culture supernatant was also higher in S. aureus 161.2 stimulated cultures (Fig. 5C). For IL-4, secreted levels wereEarly Gut Bacteria and Cytokine Responses at TwoFigure 5. S. aureus supernatant induces IFN-c producing T helper cells and soluble IFN-c after in vitro stimulation of PBMCs. In vitro stimulation of PBMCs with S. aureus 161.2 supernatant induces higher percentages of CD4+ T helper cells positive for IFN-c (A) and tends to induce higher percentages of IL-4+ positive CD4+ T helper cells (B). IFN-c and IL-10 released into culture supernatant shown in (C). Data are representative 
of 5? healthy donors. doi:10.1371/journal.pone.0049315.gundetectable or extremely low; however detectable only in supernatants from S. aureus 161.2 stimulated cells (data not shown). In contrast, IL-10 production was higher in the LGG stimulated cultures as compared to S. aureus 161.2 stimulation alone (p,0.05) (Fig. 5C).DiscussionStudies of germ free and gnotobiotic mice have uncovered the impact of the microbiota on the maturation of both innate and adaptive immune branches of the system [1]. In humans, the role of the microbiota for immune maturation is not as clear. However, there are reports of associations between microbiota composition and immune-mediated disease, although the underlying mechanisms behind these associations are still largely unknown [9]. Based on the hypothesis that the early-life gut m.Mulation at two years of age (Fig. 4A ). Similar trends were observed when analyzing colonization at one and two months of age for both IL-4 and IL-10 (data not shown).Co-colonization with lactobacilli dampens the S. aureus associated cytokine producing cell numbers at two years of ageAs early-life colonization with lactobacilli and S. aureus were associated with opposite pattern of cytokine-secreting cells at age two, we investigated early co-colonization with both, none or either of lactobacilli and S. aureus in relation to number of cytokinesecreting cells at age two after PHA stimulation. Infants were grouped according to their two-week colonization with lactobacilli and S. aureus, being colonized with both, one or none of the bacterial species (Fig. 3). From this grouping it was apparent that colonization with S. aureus in the absence of lactobacilli was associated with significantly elevated numbers of cytokine-secreting cells in comparison to the other colonization groups. Therefore, the children were re-grouped based on lactobacilli colonization at two weeks: infants colonized with S. aureus but notLactobacilli inhibits S. aureus induced T helper cell IFN-c production in vitroGiven that colonization with S. aureus in the absence of lactobacilli was associated with significantly elevated numbers of cytokine-secreting cells, we aimed to further investigate the immunostimulatory capacity of these bacteria in vitro. Supernatants from L. rhamnosus GG (LGG) and S. aureus 161.2 were added to PBMCs and intracellular IL-42 and IFN-c production was analyzed with FACS. The release of these cytokines as well as IL10 was measured with ELISA. We found higher frequencies of IFN-c (p,0.01) and tendency towards increased IL-4 (p = 0.151) producing CD4+ T helper cells induced by S. aureus 161.2 supernatant than by LGG supernatant. When both supernatants were added simultaneously to the PBMC cultures, the frequencies of IFN-c2 (p,0.01) and IL-4 (p = 0.095) producing T helper cells were increased compared to LGG alone (Fig. 5 A ). Further, IFN-c release into culture supernatant was also higher in S. aureus 161.2 stimulated cultures (Fig. 5C). For IL-4, secreted levels wereEarly Gut Bacteria and Cytokine Responses at TwoFigure 5. S. aureus supernatant induces IFN-c producing T helper cells and soluble IFN-c after in vitro stimulation of PBMCs. In vitro stimulation of PBMCs with S. aureus 161.2 supernatant induces higher percentages of CD4+ T helper cells positive for IFN-c (A) and tends to induce higher percentages of IL-4+ positive CD4+ T helper cells (B). IFN-c and IL-10 released into culture supernatant shown in (C). Data are representative of 5? healthy donors. doi:10.1371/journal.pone.0049315.gundetectable or extremely low; however detectable only in supernatants from S. aureus 161.2 stimulated cells (data not shown). In contrast, IL-10 production was higher in the LGG stimulated cultures as compared to S. aureus 161.2 stimulation alone (p,0.05) (Fig. 5C).DiscussionStudies of germ free and gnotobiotic mice have uncovered the impact of the microbiota on the maturation of both innate and adaptive immune branches of the system [1]. In humans, the role of the microbiota for immune maturation is not as clear. However, there are reports of associations between microbiota composition and immune-mediated disease, although the underlying mechanisms behind these associations are still largely unknown [9]. Based on the hypothesis that the early-life gut m.
