Immunoglobulin G (IgG) is expressed in the serum and is part of the immunoglobulin family. The monomeric 150kDa structure of IgG constitutes two identical heavy chains and two identical light chains with molecular weight of 50kDa and 25kDa, respectively. The primary structure of this antibody also contains disulfide bonds involved in linking the two heavy chains, linking the heavy and light chains and resides inside the chains. IgG is further subdivided into four classes namely, IgG1, IgG2, IgG3, and IgG4 with different heavy chains, named γ1, γ2, γ3, and γ4, respectively. Maternal IgG is the only antibody transported across the placenta to the fetus. It passively immunizes the infants.
