The shaft or stem of the Y has yet other purposes: once bound to a cell, it also attracts a cascade of toxic immune proteins from the blood to attack microbial cells. An antibody, in short, can be conceived as a molecule with multiple parts—the binding prongs that attach themselves to the antigen, and a shaft that enables it to liaise with the immune system to become a potent molecular killer. These two distinct functions of the antibody—antigen binder and immune activator, are combined in one molecule, with a form—an immunological pitchfork—that is consummately linked to its function.
