Transmission electron microscope image of negative-stained, Fortaleza-strain Zika virus (red)FLICKR, NIAIDDengue researchers around the world have been cracking open their freezers in search of serum or antibodies that might neutralize the related flavivirus, Zika. Three groups described such antibodies in the past week. In a paper published yesterday (June 27) in the PNAS, researchers from the Emory University School of Medicine in Atlanta and their colleagues described serum and monoclonal antibodies from nine patients in Thailand, where dengue is endemic. Most of the patients’ sera and some of their monoclonal antibodies were able to neutralize Zika virus in vitro, the researchers reported. But the same sera and antibodies also enhanced Zika’s ability to infect human cells in vitro.
“It’s well known in the flavivirus field that antibodies that don’t neutralize cause enhancement,” said Michael Diamond, who studies mosquito-borne pathogens at the Washington University in St. Louis and was not involved in the work. Antibody-dependent enhancement (ADE) occurs through Fc receptors, which bind the back ends of antibodies. Fc receptors are found on several cell types, including macrophages and placental epithelial cells. They internalize antibodies and may also internalize partially neutralized viral particles bound by those antibodies. This often happens in cases of secondary dengue infection, since each of the four dengue serotypes differ enough from one another that antibodies to one serotype can be poor neutralizers of another. Even sub-neutralizing concentrations of otherwise neutralizing antibodies can lead to ADE.
Because placental Fc receptors ...
