Mast cells are pivotal effector cells in the pathogenesis of allergic and inflammatory diseases. Activation of FcepsilonRI in mast cells by antigen initiates a complex series of biochemical events leading to the release and synthesis of myriads of chemical mediators and cytokines. Adenosine is an endogenous nucleoside formed from cleavage of AMP by the enzyme 5'-nucleotidase. It exerts modulating effects in a large number of cellular systems by acting through four distinct subtypes of adenosine receptors (A1, A 2A, A2B and A3) which belong to the G-protein-coupled receptor (GPCR) family. Increasing evidence have been provided to show that adenosine plays a role in the pathophysiology of asthma through a mast cell dependent mechanism. / Pharmacological studies using specific adenosine agonists and antagonists revealed that A1 receptor was responsible for the potentiating effect of adenosine with the involvement of the pertussis toxin-sensitive Galphai-protein. Conversely, inhibition of HCMC activation was mediated by A2B receptor and was accompanied by the elevation of cAMP level suggesting the participation of Galphas-protein. / Taken together, the current studies explored the dual effect of adenosine on human mast cells activation which enhanced our understanding of adenosine receptor biology. The effectiveness of adenosine in modulating the important mast cell activation pathways definitely facilitates the rational exploitation of these receptors as therapeutic targets that could be converted into clinical benefits for asthmatic patients. / To better characterize the effect of adenosine on human mast cell under asthmatic environment, we incubated HCMC under different inflammatory condition found in asthmatic, including toll-like receptor (TLR) ligands and inflammatory cytokines. Functional studies on mediator release from HCMC indicated that out of all tested substances, Peptidoglycan (PGN) pre-incubation enhanced the IL-8 synthesis from HCMC in response to low concentration of adenosine (10-9--10-7 M). / We also investigated the action of adenosine on key signal transduction pathways involved in mast cells activation. Study on intracellular calcium concentration ([Ca2+]i) revealed that low concentration of adenosine (10-8 M) through activation of PI3Kgamma significantly enhanced Ca2+ influx. In contrast, high concentration of adenosine at 10-4 M substantially inhibited [Ca2+] i in response to anti-IgE. Furthermore, investigation on intracellular signaling molecules provided evidence that adenosine at concentrations over 10-6 M does-dependently inhibited the immunoglobulin (IgE)-dependent activation of ERK, JNK or NF-kappaB pathways, whereas enhancement of IkappaBalpha was found on low concentration of adenosine. The above observation help to justify the dual action of adenosine on anti-IgE-induced mediators release from HCMC. Our investigation further suggested that adenosine may inhibit HCMC activation through a novel cAMP-dependent, but PKA- and EPAC-independent, signaling pathway. / We generated human cultured mast cells (HCMC) from human buffy coat and confirmed the expression of all adenosine receptor subtypes in them. We showed that adenosine alone did not induce HCMC degranulation and cytokine release. However, adenosine and the non-selective agonist, 5'-N-Ethylcarbox-amidoadenosine (NECA), produced a biphasic response on anti-IgE induced mast cell activation. An enhancement of HCMC activation was observed with low concentrations of adenosine and NECA (10-9--10-7 M), whereas a predominant inhibitory action was observed at concentrations higher than 10-6 M. / Yip, Kwok Ho. / Adviser: Alaster H.Y. Lau. / Source: Dissertation Abstracts International, Volume: 73-03, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 237-263). / 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, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.