Biol. Pharm. Bull. 28(3) 461—467 (2005)

Ling Cao” in China. It has been used, in traditional Chinese medicine, for treatment of various diseases. The bioactive components that have been isolated from R. rubescens are diterpenoids, including oridonin, ponicidin, rubescensin C, rubescensin D and others. Oridonin (Fig. 1) has various biological effects, such as anti-tumor, anti-bacteria, scavenging active oxygen free radicals and antimutagenetic effects. We have reported that oridonin had apoptosis-inducing activities in human melanoma A375-S2 and cervical cancer HeLa cells. Apoptosis is a conserved mode of cell death that is important for embryogenesis, morphogenesis and normal tissue homeostasis. Rapid recognition and ingestion of apoptotic cells by phagocytes prevent the release of toxic intracellular contents, thereby attenuate inflammation. The defect in apoptotic cell removal has been implicated as a cause for different types of chronic inflammation and predisposition to cancer, as well as autoimmune disease. Previous studies have demonstrated that proinflammatory cytokines potentiated phagocytosis of apoptotic neutrophils by human monocyte-derived macrophages. Serum-derived protein S enhanced clearance of early apoptotic cells. In addition to physical materials, paclitaxel, a natural diterpene with antitumor activity, was also reported to up-regulate phagocytosis capability of murine macrophages by inducing TNFa and IL-1b production. Pycnogenol, a potent free radical scanvenger, results in macrophage activation and the secretion of both TNFa and IL-1b. Macrophages are the main phagocytic cells of the innate immune system, responsible for phagocytosis of foreign particles, pathogen and unwanted cells. However, phagocytosis of apoptotic cells was regulated by mechanisms distinct from those modulating phagocytosis of particles or cells coated with Ig and complement. Cytokines play an important role in regulating macrophagic phagocytosis of various targets, particularly TNFa and IL-1b . These two cytokines exert a wide range of regulatory effect on macrophages. To examine phagocytosis, we used differentiated U937 cells as macrophage-like cells induced by 12-O-tetradecanoylphorbol-13-acetate (TPA). Majority of differentiated U937 cells adhered to the glass bottom and became flat and amoeboid in shape. Moreover, the TPA-treated U937 cells were able to engulf apoptotic U937 cells and microspheres. In the present study, we for the first time demonstrated that oridonin augmented phagocytosis of UV-irradiated apoptotic U937 cell by macrophage-like cells in a doseand time-dependent manner. The augmented effect was attenuated by anti-TNFa and antiIL-1b antibody, indicating that TNFa and IL-1b release was involved in this mechanism. Thus, we examine oridonin’s role in regulating immunological processes associated with the clearance of apoptotic cells in addition to inducing tumor cell apoptosis.