{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"IgG is a monomeric immunoglobulin, composed of two heavy chains and two light chains. This is the most abundant immunoglobulin and is approximately equally distributed in blood and tissue liquids, constituting 75% of serum immunoglobulins in humans. This is the only isotype that can pass through the placenta and bind to many kinds of pathogens. IgG protects the body against them by complement activation (classic pathway), opsonization for phagocytosis and neutralization of their toxins. There are 4 subclasses: IgG1 (66%), IgG2 (23%), IgG3 (7%) and IgG4 (4%)."}]}]}