High interferon alpha levels in placenta, maternal, and cord blood suggest a protective effect against intrauterine herpes simplex virus infection.

Interferons (IFN) are produced by the placenta during pregnancy, and they can be detected in the maternal and fetal blood. Although the antiviral potential of IFNs is well established, it remains unclear whether the IFNs associated with pregnancy can prevent transplacental spread of viral infection. The present study was undertaken in order to determine the possible protective effect of placentally produced IFN-alpha on fetal acquisition of herpes simplex virus (HSV). Nine mothers with a known history of genital HSV infection were studied. In five cases IFN-alpha was detected in the placenta, maternal, and fetal blood, whereas in three cases IFN-alpha could not be detected. in the remaining case, IFN-alpha was found only in the maternal blood. As corroborated by the serological evidence of early HSV infection in the cord blood, the single case of vertical HSV transmission was observed in the group of IFN nonproducers. Furthermore, virus transmission did not occur in cases where IFN-alpha was present in the placenta and simultaneously in the maternal and fetal circulations. Thus, the present data indicate that high levels of IFN during pregnancy may protect the fetus from acquiring a possibly fatal intrauterine HSV infection.