The severe and uncontrolled inflammatory reactions observed in the TGF-β1 knock-out mouse attests to the physiological role of TGF-β as an endogenous anti-inflammatory cytokine [42]. Even though in this study Gram-negative

E. coli stimulated substantial amount of proinflammatory cytokines, the induction of pro- and anti-inflammatory cytokines with live Gram-positive bacteria (including GIT simulated bacteria), on average, was significantly higher. Hessle et al. [13] reported that Gram-positive bacteria appeared to stimulate IL-12 production and Gram-negative bacteria stimulate IL-10 production preferentially. However, concordant with observations reported in Berg et al. [43] and in our study, Gram-negative E. coli induced the secretion Ixazomib manufacturer of significant concentrations of proinflammatory cytokines by PBMCs and the CRL-9850 cell line. While the mechanisms by which some bacteria induce the production

of IL-10 are unclear, LPS of Gram-negative bacteria may stimulate this anti-inflammatory response [43]. Compounds other than LPS in lactobacilli probably contributed to the ability of these probiotic bacteria to stimulate an anti-inflammatory cytokine response. Probiotic Obeticholic Acid mouse LAVRI-A1, LGG, B94 and BL536 induced substantial amounts of pro-and anti-inflammatory cytokines in line with previous studies [44], with the balance skewed towards the anti-inflammatory response in our study. A demonstration of the utility of this response is the finding that LGG reduced inflammation in Crohn’s disease [45]. The human gut microbiota

has been estimated recently to consist of at least 400 different species [46], and it is likely that the potency of each of these species to influence immune homeostasis is different. Indeed, cytokine profiles in co-cultures of bacteria with PBMC show marked differences between strains [23]. In addition, the effects of lactobacilli supplementation on experimental autoimmune encephalomyelitis have been shown to be highly strain-dependent [47]. It is therefore conceivable that the contradicting results Lepirudin found in the human trials can be explained partly by differences in the immunomodulatory capacity of the strains used. The fact that the killed bacteria in our study were inefficient in inducing substantial amounts of pro- and anti-inflammatory cytokines compared to live bacteria suggests that extra- and intracellular bacterial components as well as metabolites probably contribute to cytokine production [48]. Conceivably, a combination of certain bacterial fragments, metabolites produced in situ and particular structural motifs may need to interact with receptors on monocytes to induce optimal cytokine synthesis [21,49]. Cross et al. [50] and Macpherson and Harris [51] reported that live lactobacilli were more potent inducers of cytokine production in mammalian leucocytes compared to killed bacteria, similar to our findings.