Immunoglobulin molecules (antibodies) are multi-functional components of the immune system. Antibodies facilitate numerous cellular and humoral reactions to a variety of antigens, including those of the host (self) and foreign substances. Most antibodies produced as part of the normal immune response are **polyclonal**, meaning that they are produced by a number of distinct B lymphocytes, and, as a result, they each have a slightly d**ifferent specificity for the target antigen **(eg, by binding different epitopes or binding the same epitope with different affinities). However, it is possible to produce large quantities of an antibody from a single B-cell clone. Since 1985, approximately 100 **monoclonal antibodies** (mAbs) have been designated as drugs; new approvals continue to accrue. Available mAbs are directed against a large number of [[Antigens]] and used for the treatment of i**mmunologic diseases, reversal of drug effects, and cancer therapy.**