Immunoglobulin G （IgG） is a type of antibody. Representing approximately 75% of serum antibodies in humans, 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. There are four IgG subclasses （IgG1, 2, 3, and 4） in humans, named in order of their abundance in serum. Ig gamma-4 chain C region is a protein that in humans is encoded by the IGHG4 gene. If antigen persists, high affinity IgG4 is produced, which dampens down inflammation by helping to curtail FcR-mediated processes.