Antibody. Molecular graphic of the electron density surface of the antibody immunoglobulin G (IgG). This Y-shaped protein is produced by B- lymphocyte white blood cells as part of an immune response. The limbs" (upper left & right) bind to foreign antigens such as the surface proteins of invading bacteria. Binding can neutralize toxins or invading organisms, preventing them from interfering with normal cell processes. Bound antibodies can also make it easier for macrophage white blood cells to digest antigens, as well as triggering the breakdown of foreign cells by the complement system. This electron density surface shows the location of electrons in the molecule."