haptencarrier

Haptencarrier, or hapten carrier, is a term used in immunology to describe a complex in which a hapten—a small molecule that is not by itself immunogenic—is covalently bound to a larger, immunogenic carrier such as a protein or polymer. The combination enhances the ability of the hapten to provoke an antibody response and to elicit T cell–dependent immunity.

The immunological basis rests on the hapten providing the antigenic determinant recognized by B cells, while the carrier supplies T-helper epitopes. When a B cell binds the hapten portion of the conjugate, it internalizes the entire complex, processes carrier-derived peptides, and presents them to T helper cells. This interaction provides the signals required for B cell activation, class switching, affinity maturation, and the formation of memory B cells. Without a carrier, many haptens fail to induce robust or lasting immunity.

Common carriers include proteins such as keyhole limpet hemocyanin (KLH), bovine serum albumin (BSA), tetanus toxoid, and CRM197 (a non-toxic mutant of diphtheria toxin). Polysaccharides from bacterial capsules are often conjugated to these carriers to create conjugate vaccines. Linkage methods frequently involve covalent bonds through amino or carboxyl groups using chemistries like EDC/NHS coupling, periodate oxidation, or other bifunctional linkers.

Applications of haptencarrier conjugates are prominent in vaccine development, notably in conjugate vaccines that protect against encapsulated bacteria, and in diagnostic reagents or research tools. Limitations can include carrier-induced epitopic suppression, where pre-existing immunity to the carrier dampens responses to the hapten, influencing carrier selection and vaccine design.