Immunoglobulin G antibody. Molecular model of the antibody immunoglobulin G (IgG). This Y-shaped protein is produced by B-lymphocyte white blood cells as part of an immune response. Antibodies are used to fight off infections. The limbs" (upper left & right) bind to foreign antigens such as the surface proteins of invading bacteria. Binding can neutralize toxins or invading organisms and prevent them from interfering with normal cell processes. Bound antibodies can also make it easier for white blood cells to digest antigens, as well as triggering the breakdown of foreign cells."