HSV-2 DNA PERSISTENCE IN ASTROCYTES OF THE TRIGEMINAL ROOT ENTRY ZONE - DOUBLE-LABELING BY IN-SITU PCR AND IMMUNOHISTOCHEMISTRY

A previous study using an in situ polymerase chain reaction (PCR) amplification method showed persistent herpes simplex virus type 2 (HSV-2) DNA sequences in brains of experimentally infected mice, particularly in cells of the pens near the trigeminal root entry zone. The present study was undertaken to identify the CNS cell type(s) that persistently harbor HSV DNA and to define the associated pathology. Tissue sections including the trigeminal root were immunoreacted to detect cellular antigens, then an HSV sequence was amplified in situ. During acute infection, the CNS portion of the trigeminal root was focally demyelinated and contained viral antigen and HSV DNA in glial cells. Following acute infection, no infectious virus or HSV antigen was detected. Demyelinated root lesions contained cells whose nuclei were similar in size to those of astrocytes and contained HSV-2 DNA by in situ PCR. With double labeling techniques, HSV DNA-containing nuclei were often associated with glial fibrillary acidic protein immunoreactivity, but not with that of neuron-specific enolase and only rarely with galactocerebroside or transferrin immunostaining. Thus, at least some of the cells containing persistent HSV DNA are astrocytes. Since HSV DNA is detected when no infectious virus can be isolated and no HSV antigen is found, we conclude that this astrocytic infection is non-productive. While in situ hybridization methods show HSV latency-associated transcript (LAT) RNA in neuronal nuclei during latent infections in trigeminal ganglia and, occasionally, in brain, we were unable to detect HSV-2 LAT RNA in astrocytes in these lesions, which suggests that persistent HSV infection of astrocytes may differ from neuronal latency. This is the first report of a persistent, non-productive HSV infection in CNS glia.