Replication Efficiency of Influenza A Virus H9N2: A Comparative Analysis Between Different Origin Cell Types

Background: Efficient isolation and detection of low pathogenic avian influenza viruses from surveillance samples continues to be a high priority. Currently, the new cell lines are considered for supporting the replication to high virus strains titers. Objectives: The replication efficiency of a low pathogenic avian influenza virus in different origin cells was evaluated under different conditions. Materials and Methods: Chicken embryo fibroblast (CEF) cell and human alveolar epithelial cell line (A549) were infected with H9N2 at a multiplicity of infection of 0.1. The amount of infectious virus released into the cell culture supernatants at various post-infection time intervals were tittered by tissue culture infectious dose (TCID50) assay. The impact of these cells adaptation was investigated by determination the virus genes nucleotide sequences. Results: The influenza virus infectivity was not significant difference in these cells in the presence of trypsin. The results of fusion assay and determination of cellular protease confirmed that A549 cells support virus entry with or without supplemental trypsin. However, the H9N2 virus showed lower titer and infectivity in the trypsin–free infected A549 cells within longer time. The comparative sequence analysis indicated several simultaneously nucleotide substitutions were occurred in NA of the virus replicated in A549 cells resulted in two fixed amino acid changes at positions G320 to A and G414 to A up to the fifth passage. Conclusions: After seven consecutive passages of both cell cultures, the H9N2 virus showed similar antigenicity, also no change on viral titer level and virus replication behavior in adaptation was found. The results highlighted the use of A549 cells for efficient virus isolation.