Passive immunity against Junín virus in mice.

Passive immunity, naturally acquired from immune mothers or artificially induced by the administration of homologous hyperimmune serum, conferred on suckling mice a high degree of resistance against infection with Junín virus. Maternal antibodies in the circulating blood of the young were not detectable in the first days after birth, but rised rapidly from the 8th to the 20th day of lactation. By cross-foster nursing experiments it was shown that the greater part of the transmission of passive immunity occurred after birth, although there was transmission of a significant, though small part, before birth. The virus passage from mothers to offspring was excluded, since Junín virus was not recovered from brains, livers, spleens and kidneys of uninfected young, born from infected mothers.