B. Heynisch

Differential activation of host cell signalling pathways through infection with two variants of influenza A/Puerto Rico/8/34 (H1N1) in MDCK cells.

In cell culture-based influenza vaccine production, few efforts have been undertaken to characterise virus-host cell interactions in detail. Two influenza virus strains that grew to different virus titres, and differed in virus dynamics, apoptosis induction and proteome changes were observed. In order to elucidate biological mechanisms related to these differences, the induction of signalling cascades in adherent MDCK cells infected with two variants of influenza A/PuertoRico/8/34 (H1N1) was analysed. The pathways chosen for analysis are key components of the innate immune response and crucial for influenza A virus replication (NF-κB, IRF-3, PI3K-Akt, Jak-Stat, Raf/MEK/ERK, PKR/eIF2α). Interestingly, all investigated pathways were induced stronger by PR8-NIBSC than by PR8-RKI, the virus variant which results in higher virus titres. In particular, PR8-NIBSC infection lead to a higher induction of IFN-beta as well as IFN-stimulated gene expression, which was confirmed by Western blot as well as real-time PCR. Overall, results obtained clearly facilitate interpretation of observations regarding proteome changes and virus-induced apoptosis in cell culture-based vaccine manufacturing processes and support efforts towards design of improved host cell lines.

Efficient influenza B virus propagation due to deficient interferon-induced antiviral activity in MDCK cells

Influenza B virus infections are mainly restricted to humans, which is partially caused by the inability of influenza B virus NS1 protein to counteract the innate immune response of other species. However, for cell culture-based influenza vaccine production non-human cells, such as Madin-Darby canine kidney (MDCK) cells, are commonly used. Therefore, the impact of cellular pathogen defence mechanisms on influenza B virus propagation in MDCK cells was analysed in this study. Activation of the cellular antiviral defence by interferon stimulation slowed down influenza B virus replication at early time points but after 48h the same virus titres were reached in stimulated and control cells. Furthermore, suppression of the antiviral host defence by transient expression of a viral antagonist, the rabies virus phosphoprotein, could not increase influenza B virus replication. Finally, canine Myxovirus resistance (Mx) proteins showed no antiviral activity in an influenza B virus-specific minireplicon assay in contrast to the murine Mx1 protein. Taken together, these results indicate that an insufficient antiviral defence in MDCK cells promotes efficient influenza B virus replication favouring the use of MDCK cells in influenza vaccine production.