Which immunoglobulin is the only one that can cross the placenta?

The correct answer is Ig G, which is the only immunoglobulin that can cross the placenta during pregnancy. This unique ability allows maternal antibodies to be passed to the developing fetus, providing essential immune protection against infections during the early stages of life when the newborn's immune system is still maturing.

Ig G plays a crucial role in the immune response due to its ability to neutralize pathogens and enhance phagocytosis. It is the most abundant antibody in circulation, and its transport across the placenta is facilitated by specific receptors that recognize and bind to the Fc region of Ig G antibodies. This transfer is key in providing passive immunity to the infant, helping to protect against diseases for several months after birth until the baby can develop its own immune responses.

Other immunoglobulins, such as Ig A, Ig E, and Ig M, do not have this ability to traverse the placental barrier. Ig A is primarily found in mucosal areas and secretions, providing localized immunity. Ig E is involved mainly in allergic responses and protection against parasitic infections. Ig M is typically the first antibody produced in response to an infection but is larger and does not cross the placenta due to its structure. Thus, Ig G stands out as the only immunoglobulin