Broadly active inhibitor of viruses spontaneously produced by many cell types in culture

A broadly active inhibitor of viruses (vaccinia, polio 1, and vesicular stomatitis) was found in the culture fluid from many types of normal human and mouse cells in culture. Virus plaque-inhibiting activity appeared in culture fluids within a few hour after incubation of cultures with fresh medium. Peak inhibitory activity occurred within 24 h. Blockade of cellular ribonucleic acid or protein synthesis decreased appearance of the inhibitor, thereby substantiating that it is a cell-produced viral inhibitor. Inhibition of virus required the simultaneous presence of inhibitor, virus, and cells (due to the reversible nature of the inhibition of virus attachment and penetration, as shown in the accompanying paper [T. K. Hughes et al., Infect Immun. 32:454-457, 1981]). The degree of inhibitory activity depended on the animal species of origin of the inhibitor, the cell type used for assay, and the virus type used for challenge. No cell species barrier against inhibitor action was found. Strong inhibition of multicycle yields of vesicular stomatitis virus and Sindbis virus was caused by low doses of inhibitor. These specific characteristics of the present inhibitor separate it from commonly recognized inhibitors. Possible biological significance of the inhibitor is discussed.