The pectic polysaccharide from Bupleurum falcatum L. enhances immune-complexes binding to peritoneal macrophages through Fc receptor expression.

Binding of glucose oxidase-anti-glucose oxidase complexes (GAG), a model of immune complexes, to macrophages was enhanced by treatment with an acidic pectic polysaccharide, bupleuran 2IIb, from Bupleurum falcatum L. GAG binding to macrophages by bupleuran 2IIb increased in a dose-dependent fashion, and was abolished when the Pronase-treated macrophages were incubated with bupleuran 2IIb. The GAG binding enhancing activity of bupleuran 2IIb was reduced by periodate oxidation but not Pronase digestion of bupleuran 2IIb. When bupleuran 2IIb was digested with endo-polygalacturonase, the resulting enzyme resistant carbohydrate portion showed potent activity. Scatchard analysis indicated enhanced expression of the Fc receptor (FcR) on the surface by the action of bupleuran 2IIb. The enhancement of GAG binding by bupleuran 2IIb was inhibited by the presence of actinomycin D or cycloheximide. Bupleuran-2IIb-stimulated cells showed enhanced expression of both FcRI and FcRII mRNA, which were measured as PCR products. These results suggested that the endo-polygalacturonase resistant carbohydrate portion of bupleuran 2IIb is important for the expression of the activity, and that the activity of bupleuran 2IIb on GAG binding was mediated by receptors for polysaccharide on the cells. The up-regulation of the Fc receptor by bupleuran 2IIb was also suggested to mediate by de novo synthesis of the receptor protein.