Immunoglobulin G is a group of antibodies made up of chains of proteins that form a "Y" shape and have two sites that bind to pathogens. About 75% of immunoglobulin antibodies are of this type. They are secreted by B cells. It can bind to many types of pathogens, including bacteria, toxins, viruses and fungi. Its function is to immobilize pathogens (preventing their spread) and to cause them to clump together (localizing any infection).
Immunoglobulin G can be tested for for diagnostic purposes (e.g. autoimmune hepatitis) and can be administered as a pharmaceutical as part of IVIG.