An antibody (Ab), also known as an immunoglobulin (Ig), is a big, Y-shaped protein that the immune system employs to recognize and eliminate foreign substances like harmful bacteria and viruses. The antibody identifies an antigen, which is a unique molecule of the pathogen. Each tip of an antibody's "Y" has a paratope (like to a lock) that is specialized for one unique epitope (similar to a key) on an antigen, allowing these two structures to bind together precisely. An antibody can use this binding process to either flag a microbe or an infected cell for assault by other sections of the immune system or to directly neutralize it (for example, by blocking a part of a virus that is essential for its invasion).
The antigen-binding sites at both tips of the antibody come in a vast range to allow the immune system to detect millions of different antigens. The remainder of the Antibodies, on the other hand, remains essentially consistent. It is found only in a few forms that designate the antibody's class or isotype: IgA, IgD, IgE, IgG, or IgM. The constant region at the antibody's trunk contains regions important in interactions with other immune system components. In addition to some structural properties, the class defines the function activated by an antibody after binding to an antigen. Different kinds of antibodies are also produced in the body at different stages of an immune response.
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