Growth studies of parainfluenza virus (type 2)

Summary Single cycle and multiple cycle growth of type 2 parainfluenza virus in stable amnion cells was examined. Hemadsorption plaque counts constituted a reliable method for quantitative estimation of infective virus. Virus from cells grown in serum-free medium supplemented with lactalbumin hydrolysate (LH) gave a consistently lower p.f.u./hemagglutinin ratio than virus from cells grown in medium containing calf serum. Infectivity titers, however, were the same in all media at the end of a single cycle of growth. Factors are discussed which might bear on the effect of LH on the production of virus in the presence or absence of calf serum. An unstable variant of type 2 parainfluenza virus is described which is characterized by the formation of hemadsorption plaques larger than those produced by 90% of the particles in stock preparations of virus. A strain of type 2 parainfluenza virus (clone 13) free of the large plaque variant was derived from stock cultures by limiting dilution and plaque purification techniques.Supported by grant No. AI 03168 from the National Institutes of Health, United States Public Health Service.