Immunoglobulin G

IgG is the main type of antibody found in blood and extracellular fluid, allowing it to control infection of body tissues.

It is the only antibody isotype that has receptors to facilitate passage through the human placenta, thereby providing protection to the fetus in utero.

In the alternative pathway, antigens form complexes with IgG, which then cross-link macrophage receptor FcγRIII and stimulates only PAF release.

[12] Note: IgG affinity to Fc receptors on phagocytic cells is specific to individual species from which the antibody comes as well as the class.

The relative balance of these subclasses, in any immune complexes that form, helps determine the strength of the inflammatory processes that follow.

Finally, if antigen persists, high affinity IgG4 is produced, which dampens down inflammation by helping to curtail FcR-mediated processes.

[citation needed] The relative ability of different IgG subclasses to fix complement may explain why some anti-donor antibody responses do harm a graft after organ transplantation.

[citation needed] The measurement of immunoglobulin G can be a diagnostic tool for certain conditions, such as autoimmune hepatitis, if indicated by certain symptoms.

[18] Clinically, measured IgG antibody levels are generally considered to be indicative of an individual's immune status to particular pathogens.

A common example of this practice are titers drawn to demonstrate serologic immunity to measles, mumps, and rubella (MMR), hepatitis B virus, and varicella (chickenpox), among others.