Giant cell-forming variants of the Miyama strain of type 1 herpes simplex virus which differ in fusion activity.

During serial passages of a non-giant cell-forming variant (-GCr) of the Miyama strain of type 1 herpes simplex virus, a new giant cell-forming variant named +GC(81) was isolated. CPE induced by this isolate was compared with that by -GCr and also by +GC(LPV), a derivative strain of the +GC variant of the Miyama strain. Rounding of single cells was observed after infection with -GCr. Remarkable syncytial formation was induced by +GC(LPV), the syncytia containing hundreds of nuclei, while small giant cells were formed by +GC(81). The reason for the appearance of +GC variants that differ in fusion capacity is discussed.