(a) : Antibody are members of a class of proteins known as immunoglobulins. Immunoglobulins are glycoproteins in the immunoglobulin superfamily. The terms antibody and immunoglobulin are often used interchangeably. They are found in the blood and tissue fluids, as well as many secretions. In structure, they are globulins (in the $\gamma$-­region of protein electrophoresis). They are synthesized and secreted by plasma cells that are derived from the $B$ cells of the immune system.