Also known as antibodies, they are proteins found in the blood serum and in tissue fluids such as breast milk that are produced by B-lymphocyte cells of the immune system. Their function is to bind to substances in the body that are recognized as foreign antigens, which more often than not are other proteins on the surface of bacteria and viruses. The destruction of the microorganisms that bear the antigens is crucially dependent on this binding. Immunoglobulins also play an important role in allergies and hypersensitivity reactions, where they bind to antigens that are not necessarily a threat to health, but which may provide an inflammatory reaction.
See Cell-adhesion molecules, Montgomery’s areolar glands, Oxytocin, Proteins, Semaphorins