immunoglobin G comprised of a tetramer containing two L chains and two H chains.

a class of immunoglobulins that include the most common antibodies circulating in the blood of higher vertebrates and are active esp. against proteins foreign to the body such as those found in bacteria. There are four subclasses of this immunoglobin[close window

The most common serum antibody. It can pass from mother to fetus during pregnancy, and diffuse across mucosal surfaces. IgG is also present in vaginal secretions, in higher concentrations than sIgA.

antibodies IgG is the most abundant of the circulating antibodies. It readily crosses the walls of blood vessels and enters tissue fluids. IgG also crosses the placenta and confers passive immunity from the mother to the fetus. IgG protects against bacteria, viruses, and toxins circulating in the blood and lymph.