IgG, or immunoglobin G, is a type of antibody belonging to the gamma globulin category. These antibodies are primarily found in blood serum and interstitial fluid, and represent almost 80% of the antibodies circulating the human body. Their role is to protect tissue from viral, bacterial, and other toxic attacks carried in the bloodstream. By binding to these pathogenic agents, IgG stimulates a specifically-adapted immune response to fight them. This type of antibody is also involved in vaccination processes by activating what is called the memory response.