Effect of Carrier Protein Size on Hapten Immunogenicity and Antibody Affinity in Mice

Hapten immunogenicity and affinity of the antihapten response represent critical characteristics in the assessment of vaccine efficacy and quality of antibody production. The phenomenon is influenced by a multitude of factors, including the inherent characteristics of the hapten itself, the manner in which the hapten is expressed within the hapten-carrier conjugate structure, and the properties that the carrier exhibits. The preceding studies, which involved the comparison of protein carriers, did not yet resolve the role of the carrier size. The present paper examines the influence of carrier protein size on hapten immunogenicity and the affinity of the resulting antihapten antibodies. A series of novel metronidazole derivatives, designed as model haptens, were synthesized to prepare conjugates with mono-, di-, tri-, and tetramers of bovine serum albumin (BSA). The prepared immunogen constructs were designed to be equivalent in terms of hapten loading and presentation. The only distinguishing factor between the constructs was their varying carrier sizes. This approach aimed to assess the impact of carrier size in a murine immunization model. The results demonstrate that administration of even BSA dimer or larger conjugates resulted in a substantial augmentation in antihapten antibody titer and expedited generation and maturation. Thus, an enlarged protein carrier in comparison with conventional conjugate enhanced the immunogenicity of the hapten and the affinity of the antihapten antibodies produced. The study hypothesizes that using larger protein carriers could be a valuable strategy for developing vaccine candidates, particularly for weakly immunogenic haptens.