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Lactic acid bacteria (LAB) can support host health and crosstalks between ligands on bacterial cells and Toll-like receptors (TLR) are known as key inducers of these health effects. LAB-secreted bioactive factors also possess health-promoting properties but the underlying mechanisms remain to be identified. Here, we report that secreted factors of different LAB strains induce cytokine (IL-10 and TNF-α) production by THP1-differentiated human macrophages in a species- and strain-dependent manner. LAB-secreted products also drive immune-stimulating and anti-pathogenic M1-macrophage polarization. Moreover, bacterial supernatants induce species- and strain-dependent TLR2 activation. Several bacterial strains such as L. casei CCFM9 and L. brevis CCFM498 cannot activate TLR signaling, but their secreted products strongly activate TLR2. This indicates that LAB-secreted components may further boost the functional effects of bacterial strains. Our results confirm direct interactions of LAB-secreted components with TLRs, and provide novel insights in how LABs may provide immune-modulation.

Among the beneficial effects of Lactobacillus spp., the common mechanism underlying health protection is believed to be related to antioxidant activity. The antioxidant activities of cell-free suspension (CFS) and strain suspension (SS) of 13 Lactobacillus strains derived from 4 species (L. rhamnosus, L. acidophilus, L. casei, and L. fermenti) were determined. The correlation of CFSs and SSs in different cell lines, as well as the correlation among the three cell models (RAW264.7, Caco-2, and EA.hy926 cell lines), were compared. All CFSs and SSs of lactobacilli showed that they significantly inhibited the production of intracellular reactive oxygen species without creating obvious cytotoxic effects in the three mammal cell lines. These results suggested that RAW264.7, Caco-2, and EA.hy926 cell lines could be used as cell models to assay the cellular antioxidant activity of CFS and SS of lactobacilli. Thus, lactobacilli and by-products are a potential source of natural antioxidants and to reduce oxidative stress.

In this study, the effects of Lactobacillus rhamnosus CCFM0528, a new probiotic strain isolated by our laboratory, on glucose tolerance, hyperglycemia and cytokine secretion in high-fat-fed, streptozotocin-induced type 2 diabetic mice were studied. The results indicate that L. rhamnosus CCFM0528 significantly decreased fasting and postprandial 2-h blood glucose, glycosylated hemoglobin (HbA1c), endotoxin, tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-8 (IL-8) levels compared with the control group (P