Antibody

An immunoglobulin (Ig), commonly referred to as an antibody (Ab), is a large, Y-shaped protein that the immune system utilises to recognise and destroy foreign substances like harmful bacteria and viruses. An antigen is a particular pathogen molecule that the antibody detects. These two structures may bind together precisely because each "Y"-shaped tip of an antibody has a paratope (like a lock) that is specific for one particular epitope (like a key) on an antigen. An antibody can either neutralise a pathogen or an infected cell directly through this binding method, or it can mark them for attack by other immune system components (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 are equally diverse, enabling the immune system to recognise millions of distinct antigens. The remaining portion of the antibody, however, is often stable. IgA, IgD, IgE, IgG, and IgM are the only varieties that identify the antibody's class or isotype. Sites involved in interactions with other immune system elements can be found in the constant region at the antibody's trunk. Thus, in addition to some structural characteristics, the class also affects the function that an antibody initiates after attaching to an antigen. Different kinds of antibodies also differ in terms of where in the body they are produced and at what stage of an immune response.