Which immunoglobulin class cross the placenta?

Which immunoglobulin class cross the placenta?

• A. IgA
• B. IgM
• C. IgD
• D. IgG

Answer: (D)

IgG is the immunoglobulin that crosses the placenta, delivering maternal antibodies to the fetus. This transfer happens through the neonatal Fc receptor (FcRn) expressed in placental tissue, which binds the Fc portion of IgG and transports it into the fetal circulation. This provides the newborn with passive immunity during the final weeks of pregnancy and after birth. Other immunoglobulins don’t cross in significant amounts: IgM is a large pentamer and too big to pass the placental barrier; IgA is mainly secreted into mucosal surfaces and breast milk rather than across the placenta; IgD functions largely as a B cell receptor with little placental transport.

IgG is the immunoglobulin that crosses the placenta, delivering maternal antibodies to the fetus. This transfer happens through the neonatal Fc receptor (FcRn) expressed in placental tissue, which binds the Fc portion of IgG and transports it into the fetal circulation. This provides the newborn with passive immunity during the final weeks of pregnancy and after birth.

Other immunoglobulins don’t cross in significant amounts: IgM is a large pentamer and too big to pass the placental barrier; IgA is mainly secreted into mucosal surfaces and breast milk rather than across the placenta; IgD functions largely as a B cell receptor with little placental transport.