The use of new in vitro models to study the pathogeneis of the most important diseases of the respiratory tract of swine

猪繁殖与呼吸综合征(PRRS)和断奶后多系统衰竭综合征(PMWS)是世界养猪业造成经济损失最大的两种动物疾病。引起这两种主要猪病的病原分别是PRRS病毒(PRRSV)和猪圆环病毒2型(PCV2)。PRRSV和PCV2通过空气传播。空气传播的病原体需要与呼吸道的宿主细胞，如猪上皮细胞和猪肺泡巨噬细胞(PAM)相互作用，才能进入并在宿主体内传播。PCV2和PRRSV在体内和体外都具有限制性的细胞嗜性。PCV2在PAM中的复制通常很弱，但在患病动物的肺中有大量的PCV2。因此，与被广泛研究的PAM相比，猪呼吸道上皮细胞在病毒致病中可能起到意想不到的作用。到目前为止，还没有研究这些病毒与猪呼吸道上皮细胞相互作用的实验。有趣的是，两个新的猪呼吸道永生化细胞系NPTR和SJPL细胞被发现在体外分别对PCV2和PRRSV的感染和复制是允许的。因此，本研究计划的主要目的是利用这些新的永生化细胞株来研究PRRSV和PCV的病毒致病机理，以获得新的知识，改善动物健康。其具体目的是：1)利用新的PCV/NPTR感染模型研究PCV的致病机理、免疫应答调控，并利用反向遗传实验方法建立PCV毒力差异的模型；2)研究PRRSV在感染PCV的NPTR细胞中的协同作用和免疫调节作用；3)确定用SJPL细胞生产的PRRSV疫苗是否能改善免疫接种和攻击猪的免疫应答和保护作用。

The two most important animal diseases in term of economical loss in swine industry worldwide are porcine reproductive and respiratory syndrome (PRRS) and postweaning multisystemic wasting syndrome (PMWS). The etiological agents involved in those two major swine diseases are PRRS virus (PRRSV) and porcine circovirus (PCV) type 2 (PCV2), respectively. PRRSV and PCV2 are airborne transmitted. Airborne transmitted pathogens need to interact with host cells of the respiratory tract such as porcine epithelial cells and porcine alveolar macrophages (PAM) in order to be able to enter and disseminate in the host organism. PCV2 and PRRSV are known to have a restricted cell tropism in vivo and in vitro. The replication of PCV2 in PAM is usually very poor but there is a high amount of PCV2 in the lungs of sick animals. Consequently, the epithelial cells of the respiratory tract of swine may play an unexpected role in the viral pathogenesis compared to PAM, which are extensively studied. Until now, no experiment involving the study of the interaction of these viruses with epithelial cells of the respiratory tract of swine has been conducted. Interestingly, two new immortalized cell lines of the respiratory tract of swine, the NPTr and SJPL cells, have been discovered to be permissive to PCV2 and PRRSV infection and replication in vitro, respectively. Thus, the main goal of the present research proposal program is to use these new immortalized cell lines to study the viral pathogenesis of PRRSV and PCV for the acquisition of new knowledge and the improvement of the animal health . The specific objectives are: 1) to use the new PCV/NPTr infection model to study the viral pathogenesis, the immune response modulation and use the reverse genetic experimental approach to establish the existence of virulence variations between PCV types and genotypes; 2) to study the synergy and immune modulation of PRRSV in NPTr cells infected by PCV; 3) to determine if a PRRSV vaccine produced with the SJPL cells could improve the immune response and protection in vaccinated and challenged pigs.