Immunochemistry: A small non-immunogenic molecule can elicit an immune response after covalent conjugation to which type of macromolecule?

Introduction:
Small molecules (haptens) are generally not immunogenic on their own. However, when covalently linked to a large, immunogenic macromolecule, they can induce specific antibody responses. This question asks you to identify the macromolecule that provides immunogenicity upon conjugation.

Given Data / Assumptions:

• Haptens are small and non-immunogenic without a protein scaffold.
• Conjugation presents the hapten in a multivalent, T-cell-help-competent context.
• Protein carriers supply T-cell epitopes required for help-dependent antibody responses.

Concept / Approach:
The correct term for the macromolecule that confers immunogenicity is the carrier. The hapten is the small molecule; the adjuvant is a formulation component that enhances responses but is not the covalently linked scaffold; mitogens and superantigens activate many lymphocytes nonspecifically and are unrelated to hapten-carrier conjugation.

Step-by-Step Solution:

Verification / Alternative check:
Classical experiments (e.g., dinitrophenyl conjugated to keyhole limpet hemocyanin) demonstrate robust anti-hapten responses only when a protein carrier is present.

Why Other Options Are Wrong:

• Adjuvant: boosts immunity but is not the covalent scaffold.
• Hapten: the small molecule itself, not the macromolecular partner.
• Mitogen/superantigen: cause polyclonal activation, not specific hapten responses.

Common Pitfalls:
Confusing the terms hapten and carrier or assuming adjuvants must be covalently attached.

Final Answer:
Carrier