Introduction 3. Hapten -a substance that is non- immunogenic but which can react with the products of a specific immune response. Haptens are small molecules which could never induce an immune response when administered by themselves but which can when coupled to a carrier molecule Haptens have the property of antigenicity but not immunogenicity 4. Tolerogen, allergenIntroduction 3.Hapten - A substance that is non-immunogenic but which can react with the products of a specific immune response. Haptens are small molecules which could never induce an immune response when administered by themselves but which can when coupled to a carrier molecule. Haptens have the property of antigenicity but not immunogenicity. 4. Tolerogen,allergen