Immunoglobulin G （IgG） is a type of antibody. IgG is the most common type of antibody found in blood circulation. IgG molecules are created and released by plasma B cells. Each IgG antibody has two paratopes. Antibodies are major components of humoral immunity. IgG is the main type of antibody found in blood and extracellular fluid, allowing it to control infection of body tissues. By binding many kinds of pathogens such as viruses, bacteria, and fungi, IgG protects the body from infection. The measurement of immunoglobulin G can be a diagnostic tool for certain conditions, such as autoimmune hepatitis, if indicated by certain symptoms. 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.