Size, surface charge and flexibility of vinegar-baked Radix Bupleuri polysaccharide affecting the immune response

•A new polysaccharide was isolated from Vinegar-baked Radix Bupleuri.•VBCP2.5 could form polymeric micelles at 52.574 µg/ml.•VBCP2.5 with a small size and positive surface charge in stimulated bloodfluid.•VBCP2.5 exhibited beneficial immune-enhancing activity on macrophages.•Discuss the nano-characterization of VBCP2.5 that may have contributed to immune function.