Pentagalloylglucose (Penta-O-galloyl-β-D-glucose) is a gallotannin isolated from various plants. It suppressed interleukin (IL)-4 induced signal pathway in B cell, and inhibited IgE production partially caused by increasing a population of Treg cells in conjunction with Treg-inducing factors. Pentagalloylglucose possesses significant anti-rabies virus (RABV) activity.