Influenza virus: an NMR study of mechanisms involved in infection.

High resolution 1H-NMR spectroscopy has been used to study the infection of chicken embryo fibroblasts by influenza virus. Marked changes in the NMR spectrum occur when infectious influenza virus is introduced into the fibroblasts and these changes appear to depend upon the presence of active neuraminidase (EC 3.2.1.18). A crude preparation of neuraminidase from Vibrio cholerae is able to effect similar changes. Only minor spectral changes are observed in the absence of culture medium or when the viral genome material is inactivated by beta-propiolactone. Similarly, little change is seen in the NMR spectrum when amantadine, which is thought to inhibit uncoating of the virus inside the cell, or actinomycin D, which inhibits cellular nucleic acid metabolism, are incubated with fibroblasts prior to the addition of virus. The results suggest that neuraminidase, in co-operation with a factor in the infectious process, initiates a cellular event which can be monitored by NMR. The nature of this cellular mechanism is unknown, but further studies are under way to determine its importance in viral infection.