Colibacillosis in chickens caused by avian pathogenic Escherichia coli (APEC) is known to be aggravated by preceding infections with infectious bronchitis virus (IBV), Newcastle disease virus (NDV) and avian metapneumovirus (aMPV). The mechanism behind these virus-induced predispositions for secondary bacterial infections is poorly understood. Here we set out to investigate the immunopathogenesis of enhanced respiratory colibacillosis after preceding infections with these three viruses. Broilers were inoculated intratracheally with APEC six days after oculonasal and intratracheal inoculation with IBV, NDV, aMPV or buffered saline. After euthanasia at 1 and 8 days post infection (dpi) with APEC, birds were macroscopically examined and tissue samples were taken from the trachea, lungs and air sacs. In none of the groups differences in body weight were observed during the course of infection. Macroscopic lesion scoring revealed most severe tissue changes after NDV-APEC and IBV-APEC infection. Histologically, persistent tracheitis was detected in all virus-APEC groups, but not after APEC-only infection. In the lungs, mostly APEC-associated transient pneumonia was observed. Severe and persistent airsacculitis was present after NDV-APEC and IBV-APEC infection. Bacterial antigen was detected by immunohistochemistry only at 1 dpi APEC, predominantly in NDV-APEC- and IBV-APEC-infected lungs. Higher numbers of CD4+ and CD8+ lymphocytes persisted over time in NDV-APEC- and IBV-APEC-infected tracheas, as did CD4+ lymphocytes in NBV-APEC- and IBV-APEC-infected air sacs. KUL01+ cells, which include monocytes and macrophages, and TCRγδ+ lymphocytes were observed mostly in lung tissue in all infected groups with transient higher numbers of KUL01+ cells over time and higher numbers of TCRγδ+ lymphocytes mainly at 8 dpi. qPCR analysis revealed mostly trends of transient higher levels of IL-6 and IFNγ mRNA in lung tissue after IBV-APEC and also NDV-APEC infection and persistent higher levels of IL-6 mRNA after aMPV-APEC infection. In spleens, transient higher levels of IL-17 mRNA and more persistent higher levels of IL-6 mRNA were observed after all co-infections. No changes in IL-10 mRNA expression were seen. These results demonstrate a major impact of dual infections with respiratory viruses and APEC, compared to a single infection with APEC, on the chicken respiratory tract and suggest that immunopathogenesis contributes to lesion persistence.

禽致病性大肠杆菌引起的鸡大肠杆菌病(APEC) 已知会因先前感染传染性支气管炎病毒 (IBV)、新城疫病毒 (NDV) 和禽偏肺病毒 (aMPV) 而加重。这些病毒诱发的继发性细菌感染易感性背后的机制知之甚少。在这里，我们着手研究先前感染这三种病毒后增强型呼吸道大肠杆菌病的免疫发病机制。在用 IBV、NDV、aMPV 或缓冲盐水进行眼鼻和气管内接种 6 天后，肉鸡在气管内接种 APEC。在用 APEC 感染 (dpi) 后第 1 天和第 8 天安乐死后，对鸟类进行宏观检查，并从气管、肺和气囊中取出组织样本。在感染过程中没有观察到任何组的体重差异。肉眼损伤评分显示 NDV-APEC 和 IBV-APEC 感染后最严重的组织变化。组织学上，在所有病毒-APEC 组中均检测到持续性气管炎，但仅在 APEC 感染后未检测到。在肺部，主要观察到 APEC 相关的短暂性肺炎。NDV-APEC和IBV-APEC感染后出现严重且持续的气囊炎。仅在 1 dpi APEC 时通过免疫组织化学检测到细菌抗原，主要是在 NDV-APEC 和 IBV-APEC 感染的肺中。随着时间的推移，在 NDV-APEC 和 IBV-APEC 感染的气管中，CD4+ 和 CD8+ 淋巴细胞的数量持续增加，NBV-APEC 和 IBV-APEC 感染的气囊中的 CD4+ 淋巴细胞也是如此。KUL01+ 细胞，包括单核细胞和巨噬细胞，和 TCRγδ+ 淋巴细胞主要在所有感染组的肺组织中观察到，随着时间的推移，KUL01+ 细胞数量短暂增加，TCRγδ+ 淋巴细胞数量增加，主要在 8 dpi。qPCR 分析主要显示 IBV-APEC 和 NDV-APEC 感染后肺组织中 IL-6 和 IFNγ mRNA 的瞬时较高水平的趋势，以及 aMPV-APEC 感染后 IL-6 mRNA 的持续较高水平的趋势。在脾脏中，在所有共感染后观察到 IL-17 mRNA 的瞬时较高水平和更持久的 IL-6 mRNA 水平较高。没有观察到 IL-10 mRNA 表达的变化。这些结果表明，与 APEC 的单一感染相比，呼吸道病毒和 APEC 的双重感染对鸡呼吸道有重大影响，并表明免疫发病机制有助于病变持续存在。