Molecular recognition in allergic contact dermatitis. The concept of double-headed haptens.

The sensitizing capacity of double-headed haptens containing the pyrocatechol and alpha-methylene-gamma-butyrolactone groups reveals that only the pyrocatechol end is recognized as a sensitizer. Prior sensitization to the double-headed hapten provides protection against (induces immune tolerance to) further sensitization to the lactone hapten.