C-type virus particles in placentas of rhesus monkeys after maternal treatment with recombinant leukocyte A interferon.

Interferon inhibits the normal replication of C-type virus particles grown in vitro. The ability of interferon to produce a similar effect in vivo was tested in rhesus monkey placentas which are known to contain C-type virus particles. Samples of placenta from 6 monkeys treated with recombinant leukocyte A interferon (25 x 10(6) units/kg) for 7 to 21 days and from 6 control monkeys were examined in the electron microscope. Budding and immature C-type virus particles were present in every placenta examined from both interferon-treated and control monkeys. Mature particles were found in placentas from 3 of 6 monkeys in both treated and control groups. Possible explanations for the absence of detectable effects of interferon in C-type virus particle formation in these placentas are unresponsiveness of the trophoblast to interferon or inadequate exposure time to interferon of placental sites from which C-type particles are produced.