Recovery of Herpes Simplex Virus Genetic Information from Human Trigeminal Ganglion Cells following Superinfection with Herpes Simplex Virus Type 2 Temperature-sensitive Mutants
SUMMARY Explant cultures of human trigeminal ganglia were derived from 36 individuals. Those cultures which failed to release herpes simplex virus (HSV) spontaneously were superinfected at various times after establishment in vitro with a range of HSV-2 temperature-sensitive (ts) mutants. Eight cultures from six individuals contained HSV- specific genetic information which could be detected or rescued following superinfec- tion. Restriction enzyme analysis of ts + virus recovered from the ganglia of two individuals following superinfection was identical to that of endogenous HSV-1 spontaneously released from parallel cultures. Retrieval of ts + virus by this technique suggests products of the superinfecting virus activated expression of whole genomes or that spontaneous virus expression occurred unrelated to the act of superinfection. Experimental and clinical evidence in both animals and humans has established that neuronal cells within sensory ganglia are the source of latent herpes simplex virus (HSV) which periodically reactivates to cause lesions at peripheral mucocutaneous sites (Baringer, 1975; Cook et al., 1974; Stevens, 1975, 1978). In vitro culture techniques have enabled the recovery of clinically latent HSV from the sensory and autonomic ganglia (Baringer, 1974; Baringer & Swoveland, 1973; Bastian et al., 1972; Warren et al., 1977, 1978) and trigeminal nerve roots (Warren et al., 198.2) of unselected human cadavers. Restriction enzyme analysis of spontaneous HSV isolates from human trigeminal, superior cervical and vagus ganglia has shown that strains of HSV- 1 isolated from the ganglia of different individuals are readily distinguishable whereas strains isolated from different ganglia or multiple strains derived from a single ganglion within the same individual are identical (Lonsdale et al., 1979). Spontaneous reactivation of HSV from human trigeminal ganglia occurs from 7 to 45 days following explantation or co-cultivation with indicator cells (Baringer & Swoveland, 1973; Warren et al., 1977). Trigeminal ganglion cells that fail to release virus after 45 days in culture have been shown to contain HSV genetic information capable of complementing or recombining with superinfecting temperature-sensitive (ts) mutants of HSV-1 (Brown et al., 1979). In the present study, we have employed HSV-2 ts mutants as genetic probes to detect the presence of putative HSV-1 information in ganglion cells which failed to express virus during the course of in vitro culture. Restriction enzyme analysis of ts + virus rescued from ganglion cells following intertypic superinfection with HSV-2 ts mutants was performed to define the nature of the interaction between superinfecting virus and putative endogenous HSV-1 genetic