Salt-induced enhancement of measles virus yields in cultured cells

Supplementation of culture medium with MgSO4 or Na2SO4 in millimolar concentrations caused an enhanced measles virus (MV) yield from cultured quail embryo cells. MgSO4 at 25-50 mM concentrations exhibited the most pronounced and consistent stimulatory effect. MV infectivity increases ranged from 2- to 200-fold; the effect was highly reproducible for stationary monolayer, roller or microcarrier-grown cell culture types. MgSO4 also improved MV plaque development and caused MV plaque size enlargement on Vero cell monolayers. At mM concentrations MgSO4 was not operative as a MV thermostabilizing agent; rather, salt-induced enhancement of MV yields appeared to be due to intracellular events, e.g., augmented viral protein synthesis.