Effects of probiotic bacteria and their genomic DNA on TH1/TH2-cytokine production by peripheral blood mononuclear cells (PBMCs) of healthy and allergic subjects.

Among the factors potentially involved in the increased prevalence of allergic diseases, modification of the intestinal flora or lack of microbial exposure during childhood has been proposed. T(H)2-cytokines increase the production of IgE and stimulate mast cells and eosinophils, whereas T(H)1-cytokines, such as IFN-gamma, may suppress IgE synthesis and stimulate the expression of the secretory piece of IgA. Thus, a dysregulation in the expression of T(H)1- and T(H)2-cytokines may contribute to the initiation and maintenance of allergic diseases. Lactobacilli belonging to the natural intestinal microflora were reported to reduce the incidence of atopic dermatitis and the severity of allergic manifestations and to modulate T(H)1/T(H)2 responses. The mechanisms still remain to be elucidated. We sought to assess the effect of different probiotics, Lactobacillus rhamnosus GG, Lactobacillus gasseri (PA16/8), Bifidobacterium bifidum (MP20/5), and Bifidobacterium longum (SP07/3), on the T(H)1 and T(H)2 responses of peripheral blood mononuclear cells (PBMCs) from healthy subjects and from patients with allergy against house dust mite to Staphylococcus enterotoxin A (SEA) and Dermatophagoides pteronyssinus (Dpt). To elucidate the molecular basis of these effects, the effects of bacterial genomic DNA were compared with the effects of viable bacteria. PBMCs from allergic patients and from healthy donors were incubated for 24 or 48 h, respectively, with or without SEA and Dpt allergens. The effects of preincubation with live probiotic bacteria and the effect of their genomic DNA, added simultaneously to cultures and incubated for 24h, were assessed by measuring T(H)1/T(H)2-cytokine production. The tested live Gram-positive probiotic bacteria and their genomic DNA inhibited SEA- and Dpt-stimulated secretion of T(H)2-cytokines (IL-4 and IL-5) and enhanced the stimulation of IFN-gamma. This effect was dose-dependent with a dosage-optimum, which was identical for all lactic acid producing bacteria (LAB) tested (10 bacteria per PBMC) and their DNA (75 ng/ml). Based on the maximal effects achieved with LAB and their DNA, more than 50% of the effects seem to be contributed by DNA. No significant effect was induced by the control, Gram-negative Escherichia coli TG1. Lactobacilli and bifidobacteria reduced SEA-stimulated IL-4 and IL-5 production more effectively in PBMCs from healthy subjects than from allergic patients. In contrast to this, inhibition of Dpt-stimulated IL-4- and IL-5-secretion was more pronounced in cells from allergic subjects. Compared with living LAB, bacterial DNA inhibited IL-4- and IL-5-secretion in a similar manner. SEA- and even more so Dpt-stimulated IFN-gamma stimulation by living LAB was less pronounced in allergic than in healthy subjects, whereas IFN-gamma stimulation by their DNA was more pronounced in allergic subjects. The tested probiotic bacteria as well as their genomic DNA modulated the T(H)1/T(H)2 response to some allergens dose-dependently. DNA seems to contribute to 50% of the effect exerted by living bacteria in this in vitro model. The magnitude of the probiotic effects differed between healthy and allergic subjects. Whether the modulation found for the tested strains might be useful for the prevention and treatment of allergic diseases has to be assessed in clinical trials.