| Summary: | 碩士 === 國立臺灣大學 === 獸醫學研究所 === 94 === Porcine circovirus type 2（PCV2） is the necessary causative agent of postweaning multisystemic wasting syndrome（PMWS） in swine; however, a variety of co-factors including other infectious agents, are thought to be necessary for the full development of the disease. PCV2 nucleic acid and/or antigens are consistently observed in cells of monocyte/macrophage lineage and antigen-presenting cells in the lesions of PMWS-affected pigs; but no evidence of PCV2 replication was observed in these cells in vitro. To pursuit the question regarding the mechanism of PCV2 replication, porcine alveolar macrophages（PAMs）and lipopolysaccharide（LPS） were used in this study. The results revealed intranuclear signal of PCV2 and ORF1 protein were only detected in E. coli’s polysaccharide（LPS）-treated PCV2-inoculated PAMs. The PCV2 replication products corresponding to PCV2 spliced Cap mRNA and increased levels of infectious virus progeny were also successfully demonstrated in the LPS-treated PCV2-inoculated PAMs, but not in the mock LPS-treated PCV2-inoculated PAMs. The mechanism of LPS triggering PCV2 replication is not understood but may support the hypothesis that LPS is a stimulator of PCV2 replication which may contribute to the full development of PMWS in pigs during appropriate bacteria co-infection. In the HIV studies, LPS stimulation enhances the replication of HIV in monocytic-macrophage linage cells. In this study, IL-1beta、IL-8、IL-10 and TNF-alpha expressions were notably increased in the LPS-treated PCV2-inoculated PAMs when compared to the mock LPS-treated PCV2-inoculated PAMs. The stimulation of LPS is related to the activation of NF-κB which is a transcription factor with diverse functions. In the subsequent study, attempts to induce NF-κB activation and inhibition by PMA and NF-κB activation inhibitor, respectively, in PK-15 cells were proceed to investigate the possible involvement of NF-κB activation in PCV2 replication. The result showed that virus titer was mildly increased in the PMA-treated PCV2-infected PK-15 cells and NF-κB activation inhibitor-treated PCV2-infected PK-15 cells when compared to the mock-treated PCV2-infected PK-15 cells. The virus titer was notably increased in the PMA- and NF-κB activation inhibitor co-treated PCV2-infected PK-15 cells when compared to the PCV2-infected PK-15 cells. The findings suggest that Gram-negative bacteria may be an important factor in PCV2 replication. Additionally, the proinflammatory cytokine profiles are also affected by bacterial lipopolysaccharide. From the results of PK-15 cells, the inhibition of NF-κB activation may indirectly relate to the PCV2 replication.
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