Vaccinium angustifolium Root Extract Suppresses FcɛRI Expression in Human Basophilic KU812F Cells

Post-translational suppression of the high affinity IgE receptor expression on mast cells by an intestinal bacterium

Mast cells, which express the high-affinity IgE receptor (FcεRI) on their surface, play a crucial role in inducing allergic inflammation. Since mast cells are activated by crosslinking of FcεRI with IgE and allergens, the cell surface expression level of FcεRI is an important factor in determining the sensitivity to allergens. Recently, the involvement of gut microbiota in the prevalence and regulation of allergy has attracted attention but the precise underlying mechanisms are not fully understood. In this study, the effect of intestinal bacteria on cell surface expression of FcεRI was examined. Bacteroides acidifaciens type A 43 specifically suppressed cell surface expression of FcεRI on mouse bone marrow-derived mast cells (BMMCs) without reduction in FcεRI α and β-chain mRNA and total protein expression. The suppressive effect required sustained exposure to this bacterium, with a corresponding reduction in Erk activation. Inhibition of Erk decreased cell surface distribution of FcεRI in BMMCs, at least in part, through facilitated endocytosis of FcεRI. These results indicate that B. acidifaciens type A 43 suppresses cell surface expression of FcεRI on mast cells in a post-translational manner via inhibition of Erk. The suppression of FcεRI expression on mast cells by specific bacteria might be the underlying mechanism involved in the regulation of allergy by gut microbiota.

Suppressive Effects of Vaccinium angustifolium Root Extract via Down-Regulation of Activation of Syk, Lyn, and NF-κB in FcɛRI-Mediated Allergic Reactions

Vaccinium angustifolium, reported as the lowbush blueberry, has a rich polyphenolic content with which biological activities have been closely associated. In this study, the effects of V. angustifolium root extract (VAE) on the anti-FcɛRI α chain antibody (CRA-1)-induced FcɛRI-mediated signaling factors, protein tyrosine kinases (PTK), Lyn, Syk, and nuclear factor kappa-B cells (NF-κB) in KU812F cells were investigated. The total phenolic content of VAE was found to be 170±1.9 mg gallic acid equivalents/g. Western blot analysis revealed that VAE dose-dependently inhibited FcɛRI-mediated phosphorylation of PTK involving Lyn and Syk. Evaluation of intracellular reactive oxygen species (ROS) by spectrofluorometric analysis using 2′7′-dichlorofluorescin-diacetate revealed that they were reduced by VAE in a dose-dependent manner. Moreover, VAE reduced the levels of β-hexosaminidase released from CRA-1-stimulated KU812F cells. It was identified that VAE suppressed CRA-1-induced activation of NF-κB by Western blot analysis. Our results show that VAE may contribute to the inhibition of allergic actions via inactivation of basophils through the inhibition of β-hexosaminidase release and ROS production, which occurs as a result of inhibition of PTK, Syk, Lyn, and NF-κB.