Replication of animal viruses in differentiating muscle cells: influenza virus A

Cells were cultured from the breast muscle of 11- to 12-day-old chick embryos and were grown under conditions optimal for the development of the cells into terminally differentiated, fused myotubes. Myotubes were infected with influenza virus A/Ann Arbor/6/60(H2N2) at high multiplicity, and synthesis of virus-specific proteins and RNAs was detected by haemadsorption, fluorescence microscopy and/or isotope labelling and electrophoresis techniques. Provided that myotubes were maintained at temperatures below 39 degrees C after infection, production of virus components and yield of infectious virus in these cells was similar to those observed in infected chick kidney cells. However, if cells were maintained at temperatures of 39 degrees to 40 degrees C after infection, virus nucleoprotein was prominent in the nuclei, and synthesis of virus-specific polypeptides and of plus-strand RNA was reduced about fourfold to 20-fold compared to that detected at lower temperatures. Moreover, infectious virus was not produced when temperatures of 39 to 40 degrees C were used during virus replication. The results demonstrate that under suitable conditions avian myotubes formed in culture resemble epithelioid cells in their ability to support the productive replication of influenza virus.