The same proteins that mount an immune response to Zika virus infection can also harm the placenta and foetal development, a US study suggested Friday.
These antiviral proteins, known as type I interferons, have been previously found to be required to fight Zika infection in mothers.
In the new study, a team led by immunobiologist Akiko Iwasaki at Yale University, studied two different types of mouse models to explore the role interferons played in providing an immune defence for the foetuses.
One type lacked the receptor for type 1 interferon altogether, and the other had only one copy of the interferon receptor gene.
Only the latter showed signs of abnormal placental development, restricted foetal growth and death, according to results published in the US journal Science Immunology.
"The finding demonstrates that the damaging effects of the immune response to Zika virus can outweigh the benefits for foetuses," said a statement released by Yale University.
"Although type 1 interferon is critical to blocking replication of the virus, too much of it can be detrimental during pregnancy," it added. "The study results may have implications for other infection-related pregnancy complications and possible interventions."
Zika virus is carried and transmitted by the Aedes aegypti mosquito and can also be spread during sex.
Scientists have linked infections during pregnancy to stillbirths and birth defects such as microcephaly, where a baby's head is abnormally small.