Immunocytochemical localization of herpes simplex virus antigen in the trigeminal ganglia of experimentally infected mice.

The peroxidase anti-peroxidase (PAP) technique was used to study the distribution of herpes simplex virus (HSV) antigens in mouse ganglia during the acute infection and the transition into the latent infection. At 2 days after HSV inoculation by the corneal route, immunoperoxidase staining was present in occasional isolated neurons of the trigeminal ganglion and also in scattered satellite cells. By 4 days, more cells were stained with the infection centered in the medial portion of the ganglion. Inflammatory cells were present around PAP-labeled fragments from lysed cells. Stained satellite cells often with a hypertrophic appearance surrounded labeled or unlabeled neurons in a ring-like array. At 6 days after HSV inoculation, there was a decrease both in the number of cells stained and in the intensity of staining. By 8 days, HSV antigens could be detected by weak PAP staining only in neurons. Otherwise, these neurons appeared morphologically normal. No immunoperoxidase staining was present after the 8th day. These results are compatible with retrograde axoplasmic transport of HSV and cell to cell spread of virus in ganglia. Also the appearance of infected ganglion cells during the transition to latency suggests that neurons can be switched from an HSV-permissive to a non-permissive (latent) state.