Growth properties and F protein cleavage site sequences of naturally occurring human parainfluenza type 2 viruses.

The growth properties of 24 clinical isolates of PIV-2 obtained from six independent areas in Japan were examined using Vero and primary monkey kidney cells. These viruses could be subdivided into three groups on the basis of the ability of syncytium formation on the two primate cell systems. The distinct correlation between the F protein cleavability and the fusogenic effect was observed in Vero cells, and the importance of consecutive basic residues in the F protein cleavage site for efficient cleavage was suggested by the sequence analyses of their F genes. On the other hand, in PMK cells, their fusogenic activities could not be directly attributed to the F cleavability, fusion peptide sequence, and replication efficiency, indicating that unidentified structural features play an important role in cytopathic activities of naturally occurring PIV-2s.