CHARACTERIZATION OF THE PLACENTAL BARRIER TO MURINE ENTEROVIRUS INFECTION

We performed studies to characterize the mechanisms responsible for development during gestation of a placental barrier to Theiler's murine encephalomyelitis virus (TMEV) in a murine model of gestational enterovirus infection. Electron microscopy of placentae infected in early gestation revealed TMEV-induced changes in the decidua, giant cell, spongiotrophoblast, and labyrinth layers; in contrast, placentae infected in middle and late pregnancy demonstrated degenerative changes in the decidua, giant cell, and spongiotrophoblast layers hut not in the labyrinth. lmmunohistochemistry and in situ hybridization of placentae infected in early or late gestation demonstrated accumulation of monocytes/macrophages in infected, histologically damaged labyrinths, but no infiltration of immune cells into infected but histologically normal placental regions. Silver staining of placentae from dams inoculated in late gestation with inert gold beads the size of TMEV virions revealed bends within the decidua, giant cell, and spongiotrophoblast layers, but restriction of beads from labyrinths, similar to the usual distribution of TMEV in placentae infected in late pregnancy. These experiments suggest that anatomical relationships, and not systemic immune response, appear to be a major contributor to the murine placental barrier to TMEV.