In 10-day-old suckling and adult mice, reovirus type 1 adheres selectively to and penetrates membranous epithelial (M) cells. To determine when M cells first appear, when they first transport reovirus, and if reovirus adheres to and is endocytosed by other epithelial cells in the first postnatal week, we examined neonatal mouse intestine by transmission electron microscopy after reovirus type 1 exposure. At 2 days M cells accounted for 0.9% of dome epithelial cells. By 9 days M cells had increased to 7.4%. Reovirus type 1 adherence to the surface of villus and dome epithelial cells showed marked variation in 2-6-day-old animals, but by 7 days only a few absorptive cell profiles had adherent reovirus. Adherence to greater than 50% of M-cell profiles occurred in all but 2 animals, but adherence to the majority of Peyer's patch absorptive cell profiles was present only in some 4- and 5-day-old animals. Adherence to a majority of undifferentiated cell profiles occurred in some animals at all ages. Membranous epithelial cells endocytosed reovirus at all ages but only at 2 days did rare villus and dome absorptive cells endocytose reovirus into the apical cytoplasm. Thus, adherence of reovirus to the apical surface of mucosal epithelial cells is nonselective in newborn mice but becomes more selective within the first postnatal week with adherence by day 7 to most M-cell profiles, to a substantial but variable number of undifferentiated cell profiles, but to few absorptive cell profiles.

A murine model in which neurotropic retroviral infection can be studied over short periods of time was developed. Microinjection of Cas-Br-E virus into midgestation mouse embryos caused paralysis and death within 25 days after birth, in contrast to virus-infected neonates which develop disease only after 4 months. To evaluate whether antiviral drugs could cross the placental barrier and influence the course of the disease, the drug 3'-azido-3'-deoxythymidine (AZT) was administered to infected embryos through the drinking water of pregnant females. AZT treatment markedly retarded the onset and course of virus-induced central nervous system disease, permitting animals to survive beyond 4 months of age. These results are evidence for effective antiviral treatment during gestation and in the perinatal period and are of potential significance for the management of maternal transmission of the acquired immune deficiency syndrome (AIDS) virus.