Nanjing Advanced Academy of Life and Health 1 article published in JoVE Immunology and Infection Preparation of Pseudo-Typed H5 Avian Influenza Viruses with Calcium Phosphate Transfection Method and Measurement of Antibody Neutralizing Activity Xiaoyan Chang*1, Keru Zhou*1, Yanguang Liu1,2, Lian Duan3, Lichun Zhang2, Guoliang Zhang3, Haikun Wang4, Guiqin Wang1 1Nanjing Advanced Academy of Life and Health, 2Institute of Animal Bio-technology, Jilin Academy of Agricultural Sciences, 3National Clinical Research Center for Infectious Diseases, Shenzhen Third People’s Hospital, Southern University of Science and Technology, 4CAS Key Laboratory of Molecular Virology and Immunology, Institut Pasteur of Shanghai, Chinese Academy of Sciences, University of Chinese Academy of Sciences Here we describe a protocol for pseudovirus packaging and the measurement of antibody neutralizing activity.