Now, researchers from the University of Oslo and Oslo University Hospital, together with national and international collaborators, have found that the placenta distinguishes between antibodies and albumin, a finding that may reshape the future design of biologic medicines with reduced fetal exposure.

Published in Science Immunology, the study demonstrates that although the neonatal Fc receptor (FcRn) binds both IgG antibodies and albumin—the two most abundant proteins in the bloodstream—FcRn expressed in the placenta selectively transports IgG to the fetus while largely excluding albumin. The discovery resolves a longstanding question in placental biology and inspires the engineering of long-acting biologic medicines with minimal fetal exposure.