Antibody
Antibody Each antibody binds to a specific antigen ; an interaction similar to a lock and key. An antibody ( Ab ), also known as an immunoglobulin ( Ig ), is a large, Y-shaped protein produced mainly by plasma cells that are used by the immune system to identify and neutralize pathogens such as bacteria and viruses . The antibody recognizes a unique molecule of the harmful agent , called an antigen , via the Fab's variable region . Each tip of the "Y" of an antibody contains a paratope (analogous to a lock) that is specific for one particular epitope (similarly analogous to a key) on an antigen, allowing these two structures to bind together with precision. Using this binding mechanism, an antibody can tag a microbe or an infected cell for attack by other parts of the immune system, or can neutralize its target directly (for example, by blocking a part of a microbe that is essential for its invasion and survival). Depending on the antigen,