IgG is one of the immunoglobulin types that is present in large amounts in tissue fluids and blood. Each IgG antibody structure consists of the basic four-chain model of immunoglobulin. There are two identical L chains (either kappa or lambda) and two identical H chains. There are two identical antigen-binding sites in IgG. Based on minor differences in the H chains, IgG can be divided into four subclasses with distinct biological properties. IgG is the only immunoglobulin type that can cross the placenta. This helps in providing some degree of immunity to the developing fetus. IgG molecules also get secreted into the mother’s milk. When the infant ingests them, they are transported into the blood, where they generate immunity.