Proteins that mount a potent immune response to Zika virus, and help pregnant women fight the infection, can harm the placenta and foetal growth, a study has found. Researchers had previously established that these antiviral proteins, known as type I interferons, were required to fight Zika infection in mothers.

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However, it was not clear what role interferons played in providing an immune defence for the foetus. To investigate, researchers from Yale University in the US studied two different types of mouse models. 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, the researchers said. The findings, published in the journal Science Immunology, demonstrates that damaging effects of the immune response to Zika virus can outweigh the benefits for foetuses.

Researchers found that although type 1 interferon is critical to blocking replication of the virus, too much of it can be detrimental during pregnancy.
The study results may have implications for other infection-related pregnancy complications and possible interventions.