Which immunoglobulin class is able to cross the placenta from the mother to the fetus?

Which immunoglobulin class is able to cross the placenta from the mother to the fetus?

• A. IgA
• B. IgD
• C. IgE
• D. IgG

Answer: (D)

Maternal antibodies reach the fetus mainly in the form of IgG, transported across the placenta by the Fc neonatal receptor. This receptor binds the Fc region of IgG in the placental endosome and shuttles it into fetal circulation, giving the fetus passive systemic immunity before its own immune system is fully functional. Other immunoglobulin classes don’t cross the placenta in meaningful amounts: IgA is mainly secreted into mucosal surfaces and provided to the newborn via breast milk as secretory IgA; IgM is a large molecule and cannot cross, and IgD and IgE are not transferred significantly. Thus, the immunoglobulin class that can cross the placenta is IgG.

Maternal antibodies reach the fetus mainly in the form of IgG, transported across the placenta by the Fc neonatal receptor. This receptor binds the Fc region of IgG in the placental endosome and shuttles it into fetal circulation, giving the fetus passive systemic immunity before its own immune system is fully functional. Other immunoglobulin classes don’t cross the placenta in meaningful amounts: IgA is mainly secreted into mucosal surfaces and provided to the newborn via breast milk as secretory IgA; IgM is a large molecule and cannot cross, and IgD and IgE are not transferred significantly. Thus, the immunoglobulin class that can cross the placenta is IgG.