Hapten-protein antigens, synthesis

Second, the reactive species of a xenobiotic may bind to a protein, altering its antigenicity. The xenobiotic is said to act as a hapten, ie, a small molecule that by itself does not stimulate antibody synthesis but will combine with antibody once formed. The resulting antibodies can then damage the cell by several immunologic mechanisms that grossly perturb normal cellular biochemical processes. 

B Rubin. Studies on the induction of antibody synthesis against sulfanilic acid in rabbits, I. Effect of the number of hapten molecules introduced in homogeneous protein on antibody synthesis against the hapten and the new antigenic determinants. Eur J Immunol 2 5, 1972. 

A substance that after injection into the body of a vertebrate induces a specific Ab synthesis, is called an Ag. Ags are principally macromolecules, for instance proteins, polysaccharides or nucleic acids. Synthetic polymers also belong to the antigens, i.e. they can be used as, or act as, Ags. Small molecules (haptens) such as pesticides have to be coupled to a macromolecular carrier to elicit an Ab response (see section 2.3). The ability of an Ab molecule to bind an Ag or a hapten specifically is controlled by structural and chemical interactions between the ligand and the Ab at the combining site. The Ag-Ab interaction is reversible and does not involve formation of covalent bonds. The binding is a result of a variety... 

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