Which immunoglobulin is the most abundant in blood and extracellular fluid?

Immunoglobulin G (IgG) is recognized as the most abundant immunoglobulin found in blood and extracellular fluid. It accounts for approximately 70-75% of the total antibodies in the human body. IgG plays a crucial role in the immune response by providing the majority of antibody-based immunity against invading pathogens. It is essential for opsonization, neutralization of toxins and viruses, and activating complement systems, which enhance the ability of antibodies and leukocytes to clear pathogens from an organism.

IgG is characterized by its ability to cross the placenta, providing passive immunity to the fetus during pregnancy. This feature makes it particularly vital for newborns, as they receive protective antibodies before their own immune system becomes fully functional.

Other immunoglobulins, like IgA, IgM, and IgE, have important roles but are present in smaller quantities in the bloodstream. IgA is primarily found in mucosal areas and secretions like saliva and breast milk, IgM is mainly involved in the early stages of the immune response, and IgE is associated with allergic reactions and parasitic infections, making them less abundant in the general circulation compared to IgG.