H9N2禽流感病毒可引起鸡的免疫功能下降，导致疫苗免疫失败，但其机制尚不清楚。树突状细胞（DCs）是功能最强的专职抗原提呈细胞，也是多种病毒诱发宿主免疫抑制的靶细胞。前期研究中我们发现H9N2病毒及其NS1、PA-X基因可明显抑制鸡DCs的MHC-I类抗原提呈，但其作用机制仍不清楚。本项目拟以鸡骨髓源DCs为模型，研究NS1、PA-X基因对MHC-I类抗原加工、递呈过程的调控作用，及其对抗原提呈关键蛋白转录、翻译和修饰的影响，并对相关信号通路及其与关键蛋白的直接相互作用进行研究；同时对与抑制作用相关的NS1、PA-X基因的关键结构域及其氨基酸位点进行鉴定，并通过反向遗传操作技术构建H9N2病毒突变株，在鸡体内对其抑制作用进行验证。以上研究有望阐明H9N2病毒通过NS1和PA-X基因抑制宿主MHC-I类抗原提呈的分子机制，将有助于揭示H9N2病毒的免疫抑制机理，为新型疫苗的研制提供理论依据。

H9N2 subtype avian influenza virus can cause the decline of immune function in chickens, and result in the vaccination failure, however the mechanism is still unclear. Dendritic cells (DCs) are the most powerful professional antigen-presenting cells and are also the targets through which a variety of viruses caused host immunosuppression. In the previous study, we found that H9N2 virus and its NS1, PA-X genes could significantly inhibit the presentation of MHC class I antigens in chicken DCs, but the specific mechanism remains unclear. In this project, chicken bone marrow-derived DCs will be used as a model to investigate the influence of NS1, PA-X genes on the processing and presentation of MHC class I antigens, as well as the impacts on the transcription, translation and post-translational modification of the antigen-presentation associated key proteins. Moreover, the signaling pathway involved in the regulation of antigen-presentation, and the direct interactions between NS1 or PA-X proteins and the key antigen-presentation proteins will be determined. Additionally, the key domains of the NS1, PA-X genes and the target amino acid positions, related to the inhibition of the MHC class I antigens presentation, will be identified. Furthermore, the inhibitory action of the key domains and amino acid positions in NS1 and PA-X genes will be confirmed in chickens by H9N2 mutant strains which were rescued using the reverse genetics technique. The above studies are expected to elucidate the molecular mechanism by which H9N2 virus impairs host MHC class I antigen presentation through NS1 and PA-X genes, which will provide helpful insights into the immunosuppressive mechanism of H9N2 subtype avian influenza virus and contribute to the development of novel vaccines.