An in vitro latency system for herpes simplex virus type 2.

An in vitro latency system for herpes simplex virus type 2 (HSV-2) in cultured cells has been developed. Virus replication was suppressed by infection of human foetal lung cells at the supraoptimal temperature of 42 degrees C, and, following transfer of such cell cultures to the normal growth temperature of 37 degrees C, infectious virus was generally undetectable for at least 6 days. HSV-2 was reactivated by intertypic superinfection at 38.5 degrees C with temperature-sensitive mutants of HSV-1, or with human cytomegalovirus, but not by superinfection with adenovirus types 2 or 5. The HSV-1 mutant tsKsyn, which produces only immediate early polypeptides at 38.5 degrees C, was as effective as the late mutant tsIsyn, but tsK which had been irradiated with u.v. light to prevent gene expression did not reactivate HSV-2. The efficiency of reactivation was very high, since 15 to 34% of the theoretical input of infectious HSV-2 particles could be retrieved by superinfection with 0.3 p.f.u. of tsKsyn per cell. Reactivation of latent virus was not induced by cell subculture or by other treatments which alter cell metabolism. The system described here may be important for studies on the molecular basis of HSV latency.