Abstract: AIM:To isolate and characterize the anti-complementary polysaccharide from the root of Bupleurum chinense.METHODS:Bioactivity-guided fractionation and purification was used to obtain the anti-complementary polysaccharide from the hot-water extract of the root of Bupleurum chinense.The polysaccharide was characterized by various chemical and spectral analyses.The anti-complementary activities were evaluated by hemolytic assay in vitro.The action targets were identified in the system with individual complement-depleted sera.RESULTS:A homogeneous polysaccharide BC-PS2 was isolated as an anti-complementary agent.It was identified as a branched polysaccharide with an average molecular weight about 2 000 KDa,composed of Glc,Ara,Gal,and Man in the ratio 3.5:2.4:2.0:1.0,respectively,along with a trace of Rha and Xyl,and only 1.11% of protein.The main linkages of the residues of BC-PS2 include terminal,1,6-linked,1,3-linked and 1,3,6-linked Glcp,terminal and 1,5-linked Araf,terminal,1,4-linked,1,6-linked and 1,4,6-linked Galp,terminal,and,1,4-linked and 1,4,6-linked Manp.The bioassay experiments revealed that BC-PS2 inhibited complement activation on both the classical and alternative pathways,with CH50 and AP50 of(0.2220.013) and(0.3560.032) mgmL-1,respectively.Preliminary mechanism studies indicated that BC-PS2 interacted with C1q,C2,and C9 components.CONCLUSION:The results demonstrated that BC-PS2 is an anti-complementary polysaccharide,and should be important constituent of the root of Bupleurum chinense for its application in the treatment of diseases associated with the excessive activation of complement system.