What is the most abundant plasma immunoglobulin?

The most abundant plasma immunoglobulin is IgG. This immunoglobulin makes up approximately 75-80% of the total immunoglobulin pool in human serum. IgG plays a critical role in the immune system as it is responsible for neutralizing pathogens, opsonization (marking pathogens for destruction by phagocytes), and activating complement proteins, which aid in the immune response. Its ability to cross the placenta also provides passive immunity to the fetus, highlighting its significance in both individual and maternal health.

In contrast, IgA is predominantly found in mucosal areas, such as the respiratory and gastrointestinal tracts, and in secretions like saliva and breast milk, but it does not reach the same levels in plasma as IgG. IgM, while the first antibody produced in response to an infection, is present in lower concentrations in the bloodstream compared to IgG. IgE is primarily associated with allergic reactions and defense against parasitic infections, and it is normally found at very low levels in the plasma. Consequently, while all these immunoglobulins play important roles in the immune response, IgG's high concentration and multifunctionality in serum establish it as the most abundant plasma immunoglobulin.