Pathogenesis of murine cytomegalovirus infection: identification of infected cells in the spleen during acute and latent infections.

Spleen cells which replicate murine cytomegalovirus (MCMV) during acute infection in vivo were identified by electron microscopy and combined immunocytochemical staining and in situ cytohybridization. Most infected cells, as defined by in situ hybridization for viral RNA with MCMV-specific probes, were shown to be positive for factor VIII-related antigen and negative for Ia, Thy-1, and F4/80 antigens. Electron microscopic ultrastructural observations indicated that the infected cells in the spleen are predominantly sinusoidal-lining cells. We also studied reactivation of MCMV from latently infected mice by cocultivation of spleen cells with mouse embryo fibroblasts. Virus was only recovered from cells in preparations of stromal (or reticular) fragments, and not from spleen cell suspensions. Neither removal of immunoglobulin-bearing cells from the stromal fragments by panning nor depletion of Thy-1- and Ia-bearing stromal cells by treatment with monoclonal antibodies and complement reduced the frequency of reactivation of MCMV. These data suggest that T lymphocytes, mature B lymphocytes, and other Ia-bearing cells are not predominant reservoirs of latent MCMV.