Which immunoglobulin is most abundant in the serum and plays the major role in humoral immunity?

Which immunoglobulin is most abundant in the serum and plays the major role in humoral immunity?

• A. IgM
• B. IgG
• C. IgD
• D. IgA

Answer: (B)

IgG is the most abundant antibody in the bloodstream and carries the major workload of humoral immunity. In circulation it makes up the largest proportion of serum antibodies, providing widespread defense throughout the body's fluids and tissues. Its monomer form lets it diffuse easily into extracellular spaces, and after a mature immune response it undergoes class-switching and affinity maturation, yielding high-affinity antibodies with a relatively long half-life. In practice, IgG neutralizes toxins and viruses, opsonizes bacteria to promote phagocytosis, and activates the classical complement pathway, all of which are central to clearing extracellular pathogens. Other immunoglobulins have specialized roles and locations—IgM is great at early defense and complement activation but is less abundant long-term; IgA is the main antibody in secretions; IgD is largely a B-cell receptor with limited serum presence. Because of its abundance and versatile effector functions in the serum, IgG is the principal player in systemic humoral immunity.

IgG is the most abundant antibody in the bloodstream and carries the major workload of humoral immunity. In circulation it makes up the largest proportion of serum antibodies, providing widespread defense throughout the body's fluids and tissues. Its monomer form lets it diffuse easily into extracellular spaces, and after a mature immune response it undergoes class-switching and affinity maturation, yielding high-affinity antibodies with a relatively long half-life. In practice, IgG neutralizes toxins and viruses, opsonizes bacteria to promote phagocytosis, and activates the classical complement pathway, all of which are central to clearing extracellular pathogens. Other immunoglobulins have specialized roles and locations—IgM is great at early defense and complement activation but is less abundant long-term; IgA is the main antibody in secretions; IgD is largely a B-cell receptor with limited serum presence. Because of its abundance and versatile effector functions in the serum, IgG is the principal player in systemic humoral immunity.