IgG Structure and Function

Immunoglobulin G (IgG) is a 150 kDa glycoprotein found in human serum and an important mediator of the humoral immune response. IgG is composed of two heavy chains and two light chains, each divided into variable and constant domains. The variable domains are responsible for antigen binding, while the constant domains are responsible for interactions with effector molecules and effector cells. Human IgG is divided into four subclasses which although having high sequence homology, offer structural variation that significantly impacts biological function.