Activation of conventional and plasmacytoid dendritic cells and enhancement of anti-viral immune responses by Lactobacillus delbrueckii subsp. bulgaricus OLL1073R-1 and Streptococcus thermophilus OLS3059.

Dendritic cells are classified into conventional dendritic cells (cDCs) and plasmacytoid dendritic cells (pDCs), both of which play critical roles in anti-viral immune responses. Previous studies have reported that dairy consumption of yogurt fermented with Lactobacillus delbrueckii subsp. bulgaricus OLL1073R-1 and Streptococcus thermophilus OLS3059 had the effect of inhibiting viral infections. Recent studies have shown that the activation of both cDCs and pDCs and the decrease of respiratory symptoms were induced by the consumption of this yogurt. However, the components responsible for these effects and the underlying mechanisms remain unclear. Since several reports have shown that cDCs and pDCs were activated by lactic acid bacteria, we hypothesized L. bulgaricus OLL1073R-1 and S. thermophilus OLS3059 induced anti-viral immune responses by activating cDCs and pDCs. Here we demonstrated that both L. bulgaricus OLL1073R-1 and S. thermophilus OLS3059 activate cDCs and pDCs in human peripheral blood mononuclear cells. We also showed that both cDCs and pDCs were necessary for type I interferon production, whereas cDCs, but not pDCs, were essential for enhancing effector memory CD4(+) T cell responses to viral antigens when stimulated by L. bulgaricus OLL1073R-1. These findings indicate that anti-viral immune responses induced by consumption of this yogurt are mediated by both L. bulgaricus OLL1073R-1 and S. thermophilus OLS3059 through activation of cDCs and pDCs.