Efficient Replication but low titer growth of influenza virus in immortalised chick embryo fibroblasts cell line

Embryonated chicken eggs (ECEs) and mammalian origin Madin-Darby Canine Kidney (MDCK) cell line are culture systems of choice currently recommended for the isolation and propagation of influenza viruses. Spontaneously immortalized chick embryo cell lines (UMNSAH/DF-1) seem to be promising for the growth of influenza virus compared to ECEs because their use are less time-consuming, and they are free of virus and oncogenes compared to MDCK. The growth conditions influenza virus in UMNSAH/DF-1 cell were evaluated and optimized using Influenza A/Hong Kong/8/68 and B/Maryland/1/59 strains. Virus replication was assessed by haemadsorption, while virus yield was assayed by haemagglutination. In this study, UMNSAH/DF-1 cell was able to support the replication of both Influenza A/Hong Kong/8/68 and B/Maryland/1/59 viruses as demonstrated by positive haemadsorption reaction, but with infectious virus Haemagglutinin (HA) titre ranging from undetectable to very low suggesting that the cells are permissive to virus infection but do not release infectious virus particles. Virus replication could not be observed at fist and second passage when the supernatants of infected UMNSAH/DF-1 cells were used to infect fresh confluent monolayer of UMNSAH/DF-1 cells. Lectin staining, to assess the expression of α-2, 3– and α-2, 6–linked sialic acid residues on UMNSAH/DF-1 cells, revealed that both SA receptors were expressed on uninfected UMNSAH/DF-1 cells. A sustained expression of both lectins was observed in UMNSAH/DF-1 cells after infection with influenza A/HK/8/68, but not with B/Maryland/1/59 strain. In conclusion, influenza virus replicate in UMNSAH/DF-1 cells without effient release into the cell culture supernatant. The lectin staining used in this study was not able to completely clarify the reason for the defect in the release of the virus. This will remain unresolved until further studies are performed.