Influenza C virus RNA is uniquely stabilized in a steady state during primary and secondary persistent infections

The ability to establish persistent infections in vitro and in vivo has been illustrated for different human RNA viruses. However, little insight has been gained regarding the intracellular state of viral RNA species and the regulatory processes governing their long-term continuance. In this report, primary persistence of a variant of influenza C/Ann Arbor/1/50 virus in infected MDCK cells and secondary infections in human cell lines were investigated. Different PCR and staining techniques were applied for the description of low viral loads. The RNA pattern in primary persistence indicates that viral RNA synthesis is quantitatively linked to productive and nonproductive phases, with negative-strand RNA being present continuously. In single cell cultures, derived from the primary line, all clones tested were positive by nested PCR and Southern blot screening. This suggests that a true steady-state persistence of influenza C virus is established in each individual cell of the infected population. Secondary infection experiments, in terms of transfer of the persistent virus variant to different cell types, showed that a re-establishment of persistence can be accomplished in vitro. The stable persistent status remained reserved for distinct host cell lines. Hereby, vRNA is stably maintained in a cell-type specific manner, whereas gene expression (e.g. HEF glycoprotein production) occurs in a variable fashion. These data point out novel characteristics in the understanding of influenza virus persistence.