IgG antibodies 。Monomer 80%of serum antibodies 。Fix complement In blood,lymph,intestine 。Cross placenta Enhance phagocytosis; neutralize toxins viruses; protects fetus newborn 。Half-life=23days • Monomer • 80% of serum antibodies • Fix complement • In blood, lymph, intestine • Cross placenta • Enhance phagocytosis; neutralize toxins & viruses; protects fetus & newborn • Half-life = 23 days IgG antibodies