An antibody (Ab), also known as an immunoglobulin (Ig) is a large, Y-shaped protein produced mostly by plasma cells that are used by the immune system to neutralize pathogens such as pathogenic bacteria and viruses. The antibody distinguishes a unique molecule of the pathogen, 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 exact for one epitope (similarly, analogous to a key) on an antigen, permitting these two structures to bind calm with precision. By means of 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 inhibiting a part of a microbe that is essential for its invasion and survival). Depending on the antigen, the binding may impede the biological process causing the disease or may activate macrophages to destroy the foreign substance. The ability of an antibody to communicate with the other components of the immune system is mediated via its Fc region (located at the base of the “Y”), which contains a conserved glycosylation site involved in these interactions. The production of antibodies is the main function of the humoral immune system.