Answer:
An antibody, also known as an immunoglobulin, is a large Y-shaped protein produced by B- cells and used by the immune system to identify and neutralize foreign objects such as bacteria and viruses.
Each tip of the “Y” of an antibody contains a paratope (a structure 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.
Though the general structure of antibodies is very similar, a small region at the tip of the protein is extremely variable, allowing millions of antibodies with different antigen binding sites to exist. This region is known as the hypervariable region.
Five isotypes of antibodies are found in different locations and perform different specific functions.
The base of the Y plays a role in modulating immune cell activity. This region is called the Fc region, and phagocytes may bind to it to initiate phagocytosis.
Antibodies that bind to surface antigens on a bacterium attract the first component of the complement cascade with their Fc region and initiate activation of the classical complement system.