Final answer:
IgG activates the classical complement pathway, contributes to pathogen neutralization, and provides passive immunity to the fetus by crossing the placenta. It plays a significant role in immune defense against extracellular pathogens.
Step-by-step explanation:
The function of IgG in the body is multifaceted and critical for the immune response. One of its primary functions is the activation of the classical complement pathway, which is an essential part of the body's innate immunity. When IgG antibodies bind to the surface of a pathogen, they provide a platform for the complement proteins to assemble and initiate a cascade of reactions.
This cascade can lead to the lysis (destruction) of the pathogen as well as facilitate various immune responses including inflammation and opsonization, which enhance phagocytosis. Additionally, IgG antibodies are responsible for the neutralization of pathogens and can cross the placenta, providing passive immunity to the developing fetus. Unlike IgE, which is associated with the degranulation of mast cells and allergic responses, IgG does not activate mast cells but instead plays a substantial role in fighting infections by targeting extracellular pathogens both in the blood and interstitial fluid.