Hapten—Carrier Interactions and Their Role in the Production of Monoclonal Antibodies against Hydrophobic Haptens

The coupling of haptens to carrier proteins is required for the generation of antihapten antibody response. To date, different polypeptides (such as gelatin, albumin, and keyhole limpet hemocyanin) have been used to increase the immune response against haptens. Different methods of conjugation have also been used to increase the specificity of the antibody response. Our results, obtained through an analysis of the antibody response at both the polyclonal and the monoclonal levels, show that carrier proteins specifically modulate the antibody titer, the specificity of the response, the fusion efficiency, and the number of specific clones. Moreover, the affinity constants of both serum and randomly selected hybridomas directed against different haptens have been found to be exclusively modulated by carrier proteins. In addition, the results show that the carrier protein should be selected considering its possible physicochemical interaction with haptens. Data obtained suggested that any carrier is suitable for hydrophilic haptens, while the choice of the carrier for hydrophobic haptens is critical in obtaining a specific immune response. The use of specific carriers allowed the production of highly specific antibodies: even IgMs, obtained by using these carriers, were able to specifically react with hydrophobic haptens; the case of some IgM monoclonal antibodies specifically reacting with protoporphyrin IX is reported.