Which antibody is the most numerous, longest-lasting, and capable of crossing the placenta?

The correct answer is IgG, which is the most abundant antibody found in the blood and extracellular fluid, making up a significant portion of the antibodies present in the immune system. One of the distinctive features of IgG is its ability to cross the placenta, providing passive immunity to the fetus during pregnancy. This is crucial for the protection of the unborn child from infections in the early months of life when their own immune system is still developing.

IgG is also characterized by its long-lasting presence in the body, which allows it to provide sustained immunity following an infection or vaccination. Unlike other antibody types, such as IgA or IgM, IgG's longevity and placental crossing make it particularly significant in both maternal and infant immune defenses.

In contrast, IgA is primarily found in mucosal areas, such as the gut and respiratory tract, and plays a crucial role in mucosal immunity but does not cross the placenta. IgD is primarily involved in the activation of B cells but is present in very low levels in the serum and does not offer the protective qualities seen with IgG. IgM is the first antibody produced in response to an infection but does not last as long as IgG and cannot cross the placenta effectively.

Thus, IgG's