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) ampl ification 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 persistent ly harbor HSV DNA and to define the associated pathology. Tissue secti ons including the trigeminal root were immunoreacted to detect cellula r antigens, then an HSV sequence was amplified in situ. During acute i nfection, the CNS portion of the trigeminal root was focally demyelina ted and contained viral antigen and HSV DNA in glial cells. Following acute infection, no infectious virus or HSV antigen was detected. Demy elinated root lesions contained cells whose nuclei were similar in siz e to those of astrocytes and contained HSV-2 DNA by in situ PCR. With double labeling techniques, HSV DNA-containing nuclei were often assoc iated with glial fibrillary acidic protein immunoreactivity, but not w ith that of neuron-specific enolase and only rarely with galactocerebr oside or transferrin immunostaining. Thus, at least some of the cells containing persistent HSV DNA are astrocytes. Since HSV DNA is detecte d 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 gan glia and, occasionally, in brain, we were unable to detect HSV-2 LAT R NA 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 .