IN-VITRO SELECTION OF VARIANTS OF HERPES-SIMPLEX VIRUS TYPE-1 WHICH DIFFER IN CYTOPATHIC CHANGES

To analyze the mechanisms for in vitro emergence of the syncytial vari ants of herpes simplex virus type 1 (HSV-1), several cell lines were i nfected with a mixture of equal amounts of two HSV-1 variants, one syn cytial and the other non-syncytial, and changes in their relative abun dance were monitored during passage. With a combination of two variant s of the Miyama strain of HSV-1, the syncytial variant became dominant during passage in Vero, RK-13 and FL cells. On the other hand, the ra tios of the two variants remained around 1:1 during the passage in HEp -2, MGC and HEL cells. In another set of variants of the SKO strain of HSV-1, the outcomes were different from those of the Miyama strain in the FL, MGC and HEp-2 cells. The ratios of the two variants remained around 1:1 during passage in FL cells, while the non-syncytial variant became dominant during passage in MGC and HEp-2 cells. In addition, w e examined the effects of a complement and interferon-beta (IFN-beta) on the outcome of the selection. As a result, the complement slowed th e selection of a syncytial variant, whereas IFN-beta facilitated it.