No direct stimulation of human peripheral blood mononuclear cells proliferation could be detected with incubation of various AB extracts including JAB80E70 in vitro. However, ex vivo assay performed using BALB/c mice orally fed with either water (control) or JAB80E70 for 28 days indicated for the first time that extract-treated groups significantly lowered the ex vivo mitogen-stimulated lymphocyte proliferation. / Our study started with the preparations of different AB extracts using various solvent systems with or without heating. Among all AB extracts tested, the extract JAB80E70 (extracted with 70% v/v ethanol at 80°C) showed the strongest selective suppression on the growth of human leukemia NB-4 and K-562 cells. The anti-leukemia effect of JAB80E70 was also confirmed in vivo using xenografted NB-4 bearing athymic nude mice model. / Phytochemical studies suggested that the selective anti-leukemia activity of JAB80E70-W-B-1 was retained in a relatively polar sub-fraction. One compound was isolated and identified as adenosine from JAB80E70-W-B-1. To the best of our knowledge, this is the first report of the presence of adenosine in AB, even though it exhibited no anti-leukemia activity in vitro. / The mushroom Agaricus blazei (AB) is traditionally used as a remedy against various cancers, infections and immune-related diseases. In the present study, the underlying mechanisms of the anti-tumor and immunomodulatory effects of AB extracts on human leukemia cells were systematically investigated. / With bioassay-guided fractionation, a sub-fraction (JAB80E70-W-B-1) with almost 5-fold improved selective cytotoxicity towards NB-4 cells was obtained. Both JAB80E70 and JAB80E70-W-B-1 could induce apoptosis characteristic DNA fragmentation and nucleosomes enrichment in NB-4 cells. An increase in the pro-apoptotic and a decrease in the anti-apoptotic Bcl-2 family proteins expression were observed in NB-4 cells treated with JAB80E70-W-B-1. JAB80E70-W-B-1 was also found to enhance activities of caspases 3, 8 and 9 in NB-4 cells. However, the activation of caspases 3 and 9 was not affected by the inhibition of caspase 8. Furthermore, JAB80E70-W-B-1 induced apoptosis in NB-4 cells was accompanied by a significant reduction in mitochondria membrane potential and telomerase activity. These results demonstrated that JAB80E70-W-B-1 induced apoptosis in NB-4 cells was dependent on caspase activity, and involved multiple molecular pathways. / Jiang, Jingjing. / Adviser: Lau Bik San Clara. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3454. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 224-250). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.