What is the main type of antibody found in circulation?

The main type of antibody found in circulation is IgG. This immunoglobulin plays a crucial role in the immune response by recognizing and binding to specific antigens, such as pathogens, bacteria, and viruses, thereby marking them for destruction by other immune cells. IgG is the most abundant antibody in serum, comprising approximately 75-80% of the total immunoglobulin pool.

One of the key functions of IgG is its ability to provide long-lasting immunity after infections or vaccinations. It can cross the placenta, offering passive immunity to the fetus, which is critical for newborn protection early in life. Additionally, IgG is characterized by its various subclasses, which can tailor the immune response based on the type of pathogen encountered.

Other antibodies like IgA, IgM, and IgE have distinct roles; for instance, IgA is primarily found in mucosal areas and secretions such as saliva and breast milk, IgM is the first antibody produced during an immune response, and IgE is involved in allergic reactions and responses to parasites. This specialized distribution and function underscore why IgG is the predominant antibody in the circulation necessary for systemic immune defense.