Expression of beta-galactosidase in neurons of dorsal root ganglia which are latently infected with herpes simplex virus type 1

Abstract

Explantation into culture of dorsal root ganglia (DRG) latently infected with herpes simplex virus type 1 (HSV-1) causes reactivation of the virus. Previous studies have suggested that either latency-associated transcripts (LATs) were removed as an early consequence of reactivation or, alternatively, there was a population of latently infected cells which did not contain LATs. We have now attempted to detect this population of neurons by inserting a reporter gene (Escherichia coli lacZ gene), under the control of promoters other than LAT, into the HSV-1 strain 17 mutant in1814, which was used in the earlier studies. One of these promoters, the human cytomegalovirus enhancer, resulted in weak expression of β-galactosidase in DRG neurons for at least 5 months. The pattern of staining was predominantly homogeneous in neurons at 3 or 5 days post-infection or at 3 days post-explantation, and was predominantly speckled in latently infected neurons (1 to 5 months post-infection). About 30% of the β-galactosidase-positive neurons did not contain LATs by in situ hybridization. However, the detergents used to enable penetration of the substrate for β-galactosidase had also reduced the levels of the LATs; in neurons which originally had only small numbers of LATs this may have reduced levels to below those detectable by the methods used. There was, therefore, no unequivocal evidence for a population of latently HSV-1-infected cells which did not express LATs.