Department of Population Health and Reproduction, School of Veterinary Medicine, University of California at Davis, Davis, CA, USA.
Am J Respir Cell Mol Biol. 2011 Jan;44(1):24-33. doi: 10.1165/rcmb.2009-0120OC. Epub 2010 Jan 29.
The avian influenza virus H9N2 subtype has circulated in wild birds, is prevalent in domestic poultry, and has successfully crossed the species boundary to infect humans. Phylogenetic analyses showed that viruses of this subtype appear to have contributed to the generation of highly pathogenic H5N1 viruses. Little is known about the host responses to H9N2 viruses in human airway respiratory epithelium, the primary portal for viral infection. Using an apically differentiated primary human tracheobronchial epithelial (TBE) culture, we examined host immune responses to infection by an avian H9N2 virus, in comparison with a human H9N2 isolate. We found that IFN-β was the prominent antiviral component, whereas interferon gamma-induced protein 10 kDa (IP-10), chemokine (C-C motif) ligand (CCL)-5 and TNF-α may be critical in proinflammatory responses to H9N2 viruses. In contrast, proinflammatory IL-1β, IL-8, and even IL-6 may only play a minor role in pathogenicity. Apparently Toll-like receptor (TLR)-3, TLR-7, and melanoma differentiation-associated gene 5 (MDA-5) contributed to the innate immunity against the H9N2 viruses, and MDA-5 was important in the induction of IFN-β. We showed that the avian H9N2 virus induced apoptosis through the mitochondria/cytochrome c-mediated intrinsic pathway, in addition to the caspase 8-mediated extrinsic pathway, as evidenced by the cytosolic presence of active caspase 9 and cytochrome c, independent of truncated BH3 interacting domain death agonist (Bid) activation. Further, we demonstrated that FLICE-like inhibitory protein (FLIP), an apoptotic dual regulator, and the p53-dependent Bcl-2 family members, Bax and Bcl-x(s), appeared to be involved in the regulation of extrinsic and intrinsic apoptotic pathways, respectively. The findings in this study will further our understanding of host defense mechanisms and the pathogenesis of H9N2 influenza viruses in human respiratory epithelium.
H9N2 亚型禽流感病毒在野鸟中传播，在家禽中流行，并成功跨越物种界限感染人类。系统进化分析表明，该亚型的病毒似乎促成了高致病性 H5N1 病毒的产生。人们对 H9N2 病毒在人类气道呼吸上皮（病毒感染的主要门户）中的宿主反应知之甚少。使用分化的人原代气管支气管上皮（TBE）培养物，我们研究了宿主对一种禽流感 H9N2 病毒感染的免疫反应，并与一种人源 H9N2 分离株进行了比较。我们发现 IFN-β是主要的抗病毒成分，而干扰素γ诱导的蛋白 10kDa（IP-10）、趋化因子（C-C 基序）配体（CCL）-5 和 TNF-α可能在 H9N2 病毒的促炎反应中起关键作用。相反，促炎细胞因子 IL-1β、IL-8，甚至 IL-6 可能只在致病性方面发挥次要作用。显然，Toll 样受体（TLR）-3、TLR-7 和黑色素瘤分化相关基因 5（MDA-5）有助于固有免疫抵抗 H9N2 病毒，MDA-5 在诱导 IFN-β方面很重要。我们表明，禽流感 H9N2 病毒通过线粒体/细胞色素 c 介导的内在途径诱导细胞凋亡，除了 caspase 8 介导的外在途径，这可以通过细胞质中存在活性 caspase 9 和细胞色素 c 来证明，而不依赖于截断的 BH3 相互作用结构域死亡激动剂（Bid）的激活。此外，我们证明了凋亡双重调节剂 FLICE 样抑制蛋白（FLIP）和 p53 依赖性 Bcl-2 家族成员 Bax 和 Bcl-x（s）似乎分别参与了外在和内在凋亡途径的调节。本研究的结果将进一步加深我们对宿主防御机制和人呼吸道上皮中 H9N2 流感病毒发病机制的理解。
