Safe Pseudovirus-based Assay for Neutralization Antibodies against Influenza A(H7N9) Virus

Chao Qiu¹, Yang Huang¹, Anli Zhang¹, Di Tian¹, Yanmin Wan¹, Xiaoling Zhang, Wanju Zhang, Zhiyong Zhang, Zhenghong Yuan, Yunwen Hu, Xiaoyan Zhang, and Jianqing Xu

Author affiliations: Shanghai Public Health Clinical Center, Shanghai, China (C. Qiu, A. Zhang, D. Tian, Y. Wan, Xiaoling Zhang, W. Zhang, Z. Zhang, Z. Yuan, Y. Hu, Xiaoyan Zhang, J. Xu); Fudan University, Shanghai (C. Qiu, Y. Huang, A. Zhang, Z. Yuan, Xiaoyan Zhang, J. Xu); Chinese Center for Disease Control and Prevention, Beijing, China (Xiaoyan Zhang, J. Xu)

Abstract

Serologic studies are urgently needed to assist in understanding an outbreak of influenza A(H7N9) virus. However, a biosafety level 3 laboratory is required for conventional serologic assays with live lethal virus. We describe a safe pseudovirus–based neutralization assay with preliminary assessment using subtype H7N9–infected samples and controls.

A novel reassortant avian influenza A(H7N9) virus has emerged in eastern China and caused fatal infections in humans (1–3). The real-time reverse-transcription PCR (RT-PCR) is used as a diagnostic method for detection of subtype H7N9 in infected patients or birds within the window of time when virus shedding is expected. Because of the pathogen-specific immune memory response in persons with asymptomatic cases or patients who have cleared infection, serologic assays are invaluable tools for estimating the incidence and prevalence in the population affected by the outbreak. However, those studies were confined to conventional hemagglutination-inhibition (HI) or microneutralization (MN) assays that are limited to propagation of the live lethal subtype H7N9 influenza virus in biosafety level 3 (BSL-3) laboratories. We describe a rapid and safe pseudovirus-based assay for detecting subtype H7N9 neutralizing antibodies. This assay can be performed in most laboratories equipped with BSL-2 facilities.