Study of interferon production during pregnancy in mice and antiviral activity in the placenta

Although the mortality rate after herpes simplex virus type 2 inoculation was not significantly different between pregnant mice and nonpregnant mice, systemic interferon production was very high during late pregnancy compared with that in nonpregnant mice. Antiviral activity was detected in placentas from all noninfected pregnant mice (80 to 320 U/ml in 20% suspension). The antiviral activity had a broad spectrum and was also effective in the cells of other species; an antiviral effect was shown even if the cells were treated after challenge with a virus. In addition, this activity was not inactivated by antimouse interferon-neutralizing antisera. The molecular weight of this placental antiviral substance was estimated to be 200,000 to 450,000 daltons by gel filtration, and it was inactivated by heat, acid, and trypsin. Noninterferon antiviral activity (40 to 80 U/ml) was also detected in more than half the sera (61.5%) of noninfected mice in late pregnancy.