Which antibody is known to cross the placenta?

The antibody known to cross the placenta is IgG. During pregnancy, IgG antibodies are transferred from the mother to the fetus through the placenta, providing the newborn with passive immunity against pathogens the mother has been exposed to. This transfer is crucial as it helps protect the infant in the first few months of life while their own immune system is still developing.

In contrast, IgM cannot cross the placenta due to its larger size and complex structure. It is primarily produced in response to infections and is involved in the initial immune response. IgA mainly provides mucosal immunity, found in secretions like saliva, tears, and breast milk, but does not typically cross the placenta. IgD is present in small amounts in the blood and is mainly found on the surface of B cells, playing a role in the activation of B cells rather than in transplacental immunity. Overall, IgG plays a unique and vital role in fetal development and early life protection.