Protection of murine gestational tissues from picornavirus infection in the preimplantation period

Mice were inoculated with Theiler's murine encephalomyelitis virus (TMEV) o n gestational days 1-3 (pre-implantation) or days 4-5 (peri- or post-implan tation) or with control cell lysate (days 1-5). Darns were subsequently sac rificed between days 11-14 of gestation, and placentae and fetuses were har vested. Few placentae from dams inoculated with virus on days 1-3 were posi tive by virus culture (2 per cent) or in situ hybridization (6 per cent), a nd no fetuses were positive by either technique. In contrast, most placenta e from dams inoculated with virus on days 4-5 were virus-positive by cultur e (96 per cent) or in situ hybridization (100 per cent), and a moderate num ber of fetuses were also positive (30 per cent by culture, 19 per cent by i n situ hybridization). Necrosis was present more frequently in placentae fr om mice inoculated with virus on days 4-5 (55 per cent) than in placentae f rom darns inoculated with virus on days 1-3 (19 per cent) or with control c ell lysate (18 per cent). Viral infection, mononuclear inflammation and cel l necrosis were identified in the heart and great vessels of TMEV-infected fetuses. These results indicate that gestational tissues are largely protec ted from viral infection before implantation. After implantation, gestation al tissues are more readily infected and damaged by maternal picornavirus i nfection. (C) 2000 Harcourt Publishers Ltd.