In the first weeks of life, babies rely on protective proteins called antibodies, which are transferred across the placenta from the mother to the baby whilst still in the womb. Vaccines given in pregnancy aim to increase the amount of antibody in the mother's blood, so that more antibody is transferred across the placenta to the baby protecting them until they are old enough to receive infant vaccines. Antibody is transferred across the placenta by binding to specialised receptors called FcRn on the surface of placental cells. In her pump-priming project "Unravelling maternal protection: Factors affecting transplacental transfer of antibody from mother to infant," Chrissie Jones and her team studied these protective antibodies, the placental receptors and the way the antibody and receptors interact using samples collected at different stages of pregnancy and in the context of maternal infections and vaccination.
The key findings of the study are as follows:
1. Placental expression of FcRn is similar at different stages of pregnancy
This suggests that increased antibody transport across the placenta in later pregnancy is due to factors other than an increase in the amount of FcRn receptor expression
2. FcRn receptors are unlikely to be the whole story
Jones and her team used specialised microscopic techniques to visualise the location of the FcRn receptor and the antibody within the placental cells. The receptor and antibody were not localised in the same positions, suggesting that other receptors are likely to be important in the transport of antibody from mother to infant across the placenta.
3. Pregnancy, infections in pregnancy and vaccination in pregnancy are associated with differences in the functional properties of antibody
Differences in the characteristics of the antibody were present even in early pregnancy samples, suggesting that pregnancy is associated with changes in the properties of antibody and this occurs very early in gestation. Antibodies from women living with HIV had different profiles compared to those from women without HIV infection. Jones and her team also found some small differences in the characteristics ofantibody in vaccinated compared un-vaccinated pregnant women.
4. Maternal HIV infection is associated with differences in antibody-receptor interactions
Jones and her team detected differences in the way antibody binds to different receptors in the placenta according to maternal HIV infectionstatus.
These interesting findings will be explored further by Jones and her team in future studies.
A new publication by Chris Gale, Maria A Quigley, Anna Placzek et al. portrays characteristics and outcomes of neonatal SARS-CoV-2 infection in the UK.