Lactic acid bacteria inducing a weak interleukin-12 and tumor necrosis factor alpha response in human dendritic cells inhibit strongly stimulating lactic acid bacteria but act synergistically with gram-negative bacteria

Human antigen-presenting cells respond differently to gut-derived probiotic bacteria but mediate similar strain-dependent NK and T cell activation

The intestinal microbiota is essential for homeostasis of the local and systemic immune system, and particularly strains of lactic acid bacteria and Escherichia coli have been shown to have balancing effects on inflammatory conditions such as allergy and inflammatory bowel disease. However, in vitro assessment of the immunomodulatory effects of distinct strains may depend strongly on the cell type used as a model. To select the most appropriate model for screening of beneficial bacteria in human cells, the response to strains of intestinal bacteria of three types of antigen-presenting cells (APC) was compared; blood myeloid dendritic cells (DC), monocyte-derived DC and monocytes, and the effector response of natural killer cells and naïve T cells was characterized. Maturation induced by gut-derived bacteria differed between APC, with blood DC and monocytes responding with the production of IL-6 and tumour necrosis factor-alpha to bacteria, which elicited mainly IL-10 in monocyte-derived DC. In contrast, comparable IFN-gamma production patterns were found in both natural killer cells and T cells induced by all bacteria-matured APC. An inhibitory effect of certain strains on this IFN-gamma production was also mediated by all types of APC. The most potent responses were induced by monocyte-derived DC, which thus constitute a sensitive screening model.

Epithelial cells prime the immune response to an array of gut-derived commensals towards a tolerogenic phenotype through distinct actions of thymic stromal lymphopoietin and transforming growth factor-beta

Humans and other mammals coexist with a diverse array of microbes colonizing the intestine, termed the microflora. The relationship is symbiotic, with the microbes benefiting from a stable environment and nutrient supply, and the host gaining competitive exclusion of pathogens and continuously maintenance of the gut immune homeostasis. Here we report novel crosstalk mechanisms between the human enterocyte cell line, Caco2, and underlying human monocyte-derived DC in a transwell model where Gram-positive (G+) commensals prevent Toll-like receptor-4 (TLR4)-dependent Escherichia coli-induced semimaturation in a TLR2-dependent fashion. These findings add to our understanding of the hypo-responsiveness of the gut epithelium towards the microflora. Gut DC posses a more tolerogenic phenotype than conventional DC. Here we show that Caco2 spent medium (SM) induces tolerogenic DC with lower expression of maturation markers, interleukin (IL)-12p70, and tumour necrosis factor-alpha when matured with G+ and Gram-negative (G-) commensals, while IL-10 production is enhanced in DC upon encountering G+ commensals and reduced upon encountering G- bacteria. The Caco2 SM-induced tolerogenic phenotype is also seen in DC priming of naive T cells with elevated levels of transforming growth factor-beta (TGF-beta) and markedly reduced levels of bacteria-induced interferon-gamma production. Caco2 cell production of IL-8, thymic stromal lymphopoietin (TSLP) and TGF-beta increases upon microbial stimulation in a strain dependent manner. TSLP and TGF-beta co-operate in inducing the tolerogenic DC phenotype but other mediators might be involved.

Probiotics in prevention of IgE-associated eczema: a double-blind, randomized, placebo-controlled trial

BACKGROUND

An altered microbial exposure may underlie the increase of allergic diseases in affluent societies. Probiotics may alleviate and even prevent eczema in infants.

OBJECTIVE

To prevent eczema and sensitization in infants with a family history of allergic disease by oral supplementation with the probiotic Lactobacillus reuteri.

METHODS

Double-blind, randomized, placebo-controlled trial, which comprised 232 families with allergic disease, of whom 188 completed the study. The mothers received L reuteri ATCC 55730 (1 x 10(8) colony forming units) daily from gestational week 36 until delivery. Their babies then continued with the same product from birth until 12 months of age and were followed up for another year. Primary outcome was allergic disease, with or without positive skin prick test or circulating IgE to food allergens.

RESULTS

The cumulative incidence of eczema was similar, 36% in the treated versus 34% in the placebo group. The L reuteri group had less IgE-associated eczema during the second year, 8% versus 20% (P = .02), however. Skin prick test reactivity was also less common in the treated than in the placebo group, significantly so for infants with mothers with allergies, 14% versus 31% (P = .02). Wheeze and other potentially allergic diseases were not affected.

CONCLUSION

Although a preventive effect of probiotics on infant eczema was not confirmed, the treated infants had less IgE-associated eczema at 2 years of age and therefore possibly run a reduced risk to develop later respiratory allergic disease.

CLINICAL IMPLICATION

Probiotics may reduce the incidence of IgE-associated eczema in infancy.

Development of lactococcal GEM-based pneumococcal vaccines

We report the development of a novel protein-based nasal vaccine against Streptococcus pneumoniae, in which three pneumococcal proteins were displayed on the surface of a non-recombinant, killed Lactococcus lactis-derived delivery system, called Gram-positive Enhancer Matrix (GEM). The GEM particles induced the production of the proinflammatory cytokine tumour necrosis factor-alpha (TNF-alpha) by macrophages as well as the maturation of dendritic cells. The pneumococcal proteins IgA1 protease (IgA1p), putative proteinase maturation protein A (PpmA) and streptococcal lipoprotein A (SlrA) were anchored in trans to the surface of the GEM particles after recombinant production of the antigens in L. lactis as hybrids with a lactococcal cell wall binding domain, named Protein Anchor domain (PA). Intranasal immunisation with the SlrA-IgA1p or trivalent vaccine combinations without additional adjuvants showed significant protection against fatal pneumococcal pneumonia in mice. The GEM-based trivalent vaccine is a potential pneumococcal vaccine candidate that is expected to be easy to administer, safe and affordable to produce.