IgG is the abbreviation of immunoglobulin G: which is a class of circulating antibodies predominant in the blood. IgG is the main antibody found in humans. It is part of the adaptive immune system. When an IgG antibody recognizes an antigen, it forms a so-called Circulating Immune Complex (CIC) and attracts phagocytes to destroy this CIC. IgG is divided into four sub-classes, IgG1, IgG2, IgG3 and IgG4. When an IgG binds to its antigen, the shape of the IgG changes and can be recognised by IgG receptors. IgG is believed to play a role in delayed food allergy.