IgG

Overview
  • IgG is a particular isotype of Antibody (see page). IgG is the primary isotype of antibody produced following the complete maturation of Humoral Immunity to a microbe.
Structure
  • IgG exists as a single, free-floating antibody. Because of its small size, IgG is the isotype of antibody which is best able to permeate the body's tissues and is thus found in the plasma as well as the interstitial fluid.
Function
  • Binding of multiple IgG molecules to an antigen is a potent inducer of Complement. Furthermore, the Fc Region of IgG induces phagocytosis of innate immune cells such as Macrophages, Dendritic Cells, and Neutrophils. In some cases, binding of IgG can interfere with the function of critical microbial proteins or render microbes incapable of binding to host cells.
Diagnosis
  • Because IgG is the primary isotype of antibody produced following complete maturation of Humoral Immunity its titers generally rise late during a primary infection as titers of IgM begin to decline. Furthermore, long-lived Plasma Cells often synthesize and secrete IgG years after the infection has cleared. Because of these properties of Humoral Immunity, the presence of antigen-specific IgG titers in a patient indicates that the primary infection occurred at the very least months or potentially years prior.