IgG?is present in large quantities in the human serum. It constitutes about 10-20% of the plasma proteins.?IgG is composed of glycoproteins, out of which it is 82-96% proteins and 4-18% carbohydrates.?It consists of four sub-classes?i.e?IgG1, IgG2, IgG3, and IgG4. IgG is composed of four polypeptide chains-two heavy chains (γ?chains)?and two light chains (κ or λ?chains)?which are linked by inter-chain?disulfide?bonds.?The heavy chains consist of a N-terminal variable domain (VH) and three constant domains (CH1, CH2, CH3). A hinge region exists between the CH1 and CH2 region. The light chains have one?N-terminal variable domain (VL) and?one?constant domain?(CL). The heavy and the light chains are linked at VH and CH1 domain to form the Fab arm (Fragment antigen binding).?The antigen binds to the V regions of the?antibody.
IgG antibody subtype is the most abundant serum immunoglobulins of the immune system. It is secreted by B cells and is found in blood and extracellular fluids and provides protection from infections caused by bacteria, fungi and viruses. Maternal IgG is transferred to fetus through the placenta that is vital for immune defence of the neonate against infections.
