Immunoglobulin G (
IgG) is a type of
antibody. It is a protein complex composed of four
peptide chains—two identical heavy chains and two identical light chains arranged in a Y-shape typical of antibody
monomers. Each IgG has two
antigen binding sites. Representing approximately 75% of
serum antibodies in humans, IgG is the most common type of antibody found in the circulation. IgG molecules are created and released by
plasma B cells.