Porcine Respiratory Coronavirus as a SARS Model

描述（由申请人提供）：严重急性呼吸系统综合征（SARS）是由新型冠状病毒（CoV）引起的一种新出现的全球人类疾病，具有重大的经济影响和重大的生物恐怖主义潜力。肺是与疾病表现相关的靶器官，尽管部分患者会出现腹泻。与SARS发病机制有关的尚未解决的问题包括“超级传播者”、非典型肺炎和变异性腹泻诱导的机制，以及多微生物感染在SARS不同严重程度中的作用。宿主免疫因子，特别是促炎细胞因子可能在严重的肺损伤中起作用，正如我们在猪呼吸道疾病研究中观察到的那样。在没有明确了解类固醇和干扰素对呼吸道疾病的影响的情况下，广泛使用类固醇和干扰素治疗SARS患者，有必要在呼吸道冠状病毒感染易感的动物模型中研究它们的影响。虽然灵长类动物易感染SARS冠状病毒，但它们有限的可用性和费用阻碍了对SARS发病机制的全面研究。在小鼠模型中，冠状病毒或流感病毒感染的临床病理表现与人类不同，而在猪中，它们模仿人类疾病。猪呼吸道的解剖、生理和免疫系统与人类非常相似，为人类病毒性呼吸道疾病的研究提供了独特的动物模型。猪呼吸道冠状病毒（PRCV）是肠道冠状病毒传染性胃肠炎病毒（TGEV）的刺突缺失突变体，其在肺部的初始复制与SARS冠状病毒具有惊人的致病相似性。有趣的是，即使在无症状的猪中，PRCV也总是引起与非典型肺炎相似的肺部病变。我们的研究表明，多微生物共感染通过多种机制影响PRCV感染、病变和疾病的严重程度。这些包括促炎细胞因子的库或在肺中诱导的细胞浸润，以及感染的多种细胞类型。因此，我们的目的是确定类固醇和与呼吸道病毒或细菌衍生成分（以及诱导的细胞因子）共感染对猪sars样呼吸道冠状病毒（PRCV）感染严重程度的影响。我们的具体目的是：1)评估皮质类固醇治疗感染PRCV的猪是否会影响PRCV诱导的细胞因子或对PRCV获得性免疫以及PRCV感染和疾病的后续过程（模拟类固醇对SARS患者的影响）；2)探讨既往感染远亲（尼多病毒科）低致病性呼吸道病毒病原体（动脉病毒，PRRSV）对随后PRCV感染和疾病（模拟SARS双重冠状病毒和不同呼吸道冠状病毒感染）的影响；3)探讨首次感染PRCV后再感染呼吸道病毒病原体猪流感病毒对PRCV感染和发病的影响（模拟SARS冠状病毒和流感双重感染）；4)确定猪同时感染两种具有不同组织倾向的抗原性相关冠状病毒（PRCV，呼吸道和TGEV，肠道）对PRCV/TGEV重组体产生和冠状病毒感染和疾病（模拟SARS超级传播者伴腹泻）的影响；5)研究依次接种猪PRCV和细菌细胞壁组分对细胞因子产生和疾病的影响（模拟细菌共感染对SARS细菌共感染的影响）。

DESCRIPTION (provided by applicant): Severe acute respiratory syndrome (SARS) is a newly emerging global disease of humans with a major economic impact and significant bioterrorism potential caused by a new strain of coronavirus (CoV). The lung is the target organ related to the disease manifestations, although diarrhea occurs in some patients. Unresolved questions related to SARS pathogenesis include the mechanisms for "superspreaders" and the atypical pneumonia and variable diarrhea induced and the role of polymicrobial infections in the variable severity of SARS. Host immune factors, especially proinflammatory cytokines may play a role in the severe pulmonary damage, as observed in our studies of respiratory disease in pigs. The widespread use of steroids and IFNs for treatment of SARS patients without a clear understanding of their impact on respiratory disease, necessitates studies of their impact in an animal model susceptible to respiratory CoV infection. Although primates are susceptible to SARS CoV, their limited availability and expense hampers comprehensive studies of SARS pathogenesis. In mouse models, the clinicopathological manifestations of CoV or influenza viral infections differ from in humans whereas in pigs they mimic the human disease. The anatomy, physiology and immune system of the pig respiratory tract closely resembles that of man, providing a unique animal model for the study of viral respiratory disease of humans. The porcine respiratory CoV (PRCV), a spike deletion mutant of the enteric CoV transmissible gastroenteritis virus (TGEV), shows striking pathogenetic similarities to SARS CoV in its primary replication in lung. Of interest, PRCV invariably induces similar lung lesions with atypical pneumonia, even in asymptomatic pigs. Our studies suggest that polymicrobial co-infections influence the severity of PRCV infection, lesions and disease via multiple mechanisms. These include the repertoire of proinflammatory cytokines or the cell infiltrates induced in lung, and the multiple cell types infected. Therefore our aim is to determine the influence of steroids and coinfections with respiratory viruses or bacterial derived components (and the cytokines induced) on the severity of a SARS-like respiratory coronavirus (PRCV) infection of swine. Our Specific Aims are: 1) To assess if corticosteroid treatment of PRCV-infected pigs has an impact on cytokines induced by PRCV or acquired immunity to PRCV and the subsequent course of PRCV infection and disease (mimic impact of steroids on SARS patients); 2) To investigate the impact of prior infection with a distantly related (Nidovirales) low pathogenic respiratory viral pathogen (arterivirus, PRRSV) on subsequent PRCV infection and disease (mimic dual SARS CoV and distinct respiratory CoV infections); 3) To explore the impact of initial infection with PRCV followed by subsequent infection with the respiratory viral pathogen swine influenza virus on PRCV infection and disease (mimic dual infections with SARS CoV and influenza); 4) To determine the impact of concurrent infection of pigs with two antigenically related coronaviruses with distinct tissue tropisms (PRCV, respiratory and TGEV, enteric) on generation of PRCV/TGEV recombinants and coronavirus infection and disease (mimic SARS superspeaders with diarrhea); 5) To examine the impact of sequential inoculation of pigs with PRCV followed by bacterial cell wall components on cytokine production and disease (mimic impact of bacterial coinfections on bacterial coinfections on SARS).