Regulation of Maternal–Fetal Virus Transmission in Immunologically Reconstituted SCID Mice Infected with Lactate Dehydrogenase-Elevating Virus

Immunodeficient SCID (C.B-17 scid/scid) mice with persistent lactate dehydrogenase-elevating virus (LDV) infection failed to produce IgG anti-LDV antibodies, and during chronic infection transmitted virus infection to 95% of their offspring. In contrast, normal mice infected 15 or more days prior to giving birth produced IgG anti-LDV antibodies and transmitted LDV infection to only 0–46% of their fetuses. Transplacental transmission of LDV infection was dependent on the timing of maternal infection. Adoptive transfer of immune competence to LDV-infected SCID mice resulted in fetal protection from maternally transmitted virus infection. Fetal protection correlated with the presence of maternal IgG anti-LDV but not with fetal levels of IgG anti-LDV, and the levels of viremia in nonimmune SCID mice did not affect transplacental virus transmission. These results demonstrate the importance of maternal immunity in protecting the fetus from infection, and validate the use of this mouse model for investigation of immune mechanisms of transplacental virus transmission.