Which immunoglobulin is present in the highest concentration in normal human serum?

In normal human serum, Immunoglobulin G (IgG) is present in the highest concentration, typically making up about 70-75% of the total immunoglobulin pool. This robust presence is significant because IgG plays a crucial role in the immune response, particularly in recognizing and neutralizing pathogens such as bacteria and viruses. It is the only immunoglobulin that can cross the placenta, providing passive immunity to the fetus during pregnancy.

IgG's ability to efficiently activate complement and enhance opsonization makes it vital for both adaptive and innate immunity. This concentration and functionality underscore its importance as a primary antibody during infections and its central role in immunological memory.

In contrast, other immunoglobulins such as IgA, which is mainly found in mucosal areas and secretions; IgM, which is the first antibody produced during an immune response; and IgD, which plays more of an auxiliary role in B-cell activation, are present in significantly lower amounts in serum compared to IgG. Thus, IgG's predominance in serum is key to its effective protective mechanisms against a wide range of pathogens.