A type of protein found in blood and tissue fluids, also known as an antibody. Such proteins are produced by B-lymphocytes (a type of white blood cell), and their function is to bind to substances in the body that are recognized as foreign antigens. This binding is crucial for the destruction of antigenbearing microorganisms. Immunoglobulins also play a key role in allergies and hypersensitivity reactions. Immunoglobulin G (IgG) is the major class of immunoglobulin of the 5 in the blood (IgA, IgD, IgE, IgG, and IgM). Its molecule consists of 2 parts: 1 binds to an antigen; the other binds to other cells, which then engulf the microorganisms bearing the antigen. Immunoglobulins can be extracted from the blood of people who have recovered from certain infectious diseases and used for passive immunization.


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