antibody (Ab) /an″tibod′ē/ [Gk, anti + AS, bodig] , a protein produced by plasma cells that can identify and neutralize pathogens, also known as immunoglobulin (Ig). Monomeric immunoglobulins consist of two heavy chains and two light chains, both having a constant region and a variable region. The variable region binds the antigen and needs to be highly variable in order to be able to recognize as many different antigens possible. Different types of heavy chains characterize the five structurally distinct classes. Also called immunoglobulin. See also immune response.
