Houttuynia cordata Thunb.is a traditional herb used for clearing heat and eliminating toxins,and has also been used for the treatment of severe acute respiratory syndrome (SARS).In vitro,the crude H.cordata polysaccharides (CHCP) exhibited potent anti-complementary activity through both the classical and alteative pathways by acting on components C3 and C4 of the complement system without interfering with the coagulation system.This study was to investigate the preventive effects of CHCP on acute lung injury (ALI) induced by hemorrhagic shock plus lipopolysaccharide (LPS) instillation (two-hit) and LPS-induced fever in rats.CHCP significantly attenuated pulmonary injury in the "two-hit" ALI model by reducing pulmonary edema and protein exudation in bronchoalveolar lavage fluid (BALF).In addition,it reduced the deposit of complement activation products in the lung and improved oxidantantioxidant imbalance.Moreover,CHCP administration inhibited fever in rats,reduced the number of leukocytes and restored serum complement levels.The inhibition on the inappropriate activation of complement system by CHCP may play an important role in its beneficial effects on inflammatory diseases.The anti-complementary polysaccharides are likely to be among the key substances for the heatclearing function of H.cordata.