Response of cloned progeny of clinical isolates of herpes simplex virus to human leukocyte interferon.

First- and third-generation cloned progeny viruses were derived from clinical isolates of herpes simplex virus and examined for their sensitivities to human interferon by inhibition of plaque formation in Vero cells. The dose-response curves obtained with the first- and third-generation clones were similar to those obtained with the parental isolates, and both the parent and the clones showed similar sensitivities to interferon. These results suggest that clinical isolates of herpes simplex virus consist of a homogeneous population of virus particles with respect to interferon sensitivity. The dose-response curves obtained with herpes simplex virus demonstrated a shallower slope than those obtained with vesicular stomatitis virus. Vesicular stomatitis virus plaque formation as completely inhibited at high concentrations of interferon, whereas complete inhibition of plaque formation by herpes simplex virus did not occur at the highest concentration of interferon used. Cloned progeny were derived from plaques appearing in the presence of high concentrations of interferon. The dose-response curves and interferon sensitivities of these clones were similar to those of the parent and third-generation clone from which they were derived. There was no evidence for genetic heterogeneity with respect to interferon sensitivity.