Veterinary Immunology and Serology

HAPTEN

• Haptens are usually non-protein substances of low molecular weight having very little or no antigenic property but acquire antigenicity when they are coupled to a protein (carrier molecule).
• Haptens are incapable of inducing antibody formation by themselves but can react specifically with antibodies.They are called partial antigen.
• The term hapten is derived from Greek haptein mean ‘to fasten’.
• A chemical to be tested as a determinant of specificity was attached to an aromatic amine such as aniline (aniline, p-amino benzoic acid, p- amino benzene sulphonic acid, p-amino phenyl arsonic acid), then diazotized and coupled to a protein.
• The resulting product was called a conjugated antigen or azoprotein.
• It is possible to study the immune response of a well-defined chemical by conjugating to a protein molecule.
• Hapten may be complex or simple molecule.
• Complex hapten is large molecular weight, polyvalent compound.
• When they combine with antibody prepared against the complete antigenic complex (new antigen) a visible precipitation is formed.
• Simple hapten  is a low molecular weight, univalent compound. When they combine with antibody prepared against complete antigenic complex, no visible precipitation is formed.

• Examples: Penicillin, Dinitro Phenyl (DNP) etc.