Epitopic suppression in synthetic vaccine models: analysis of the effector mechanisms.

The induction of an immune response against synthetic peptides usually requires the use of an immunogenic carrier. The use of tetanus toxoid (TT) has been proposed for this purpose as it is highly immunogenic and has been used extensively in humans. Previous studies have demonstrated that an epitope-specific suppression of IgG antibody responses occurs when mice previously primed with TT are subsequently immunized with SODP, a haptenic epitope linked to TT. In the present investigation, we characterized the effector populations which regulate anti-SODP antibody responses in TT/TT-SODP immunized mice. In vitro studies showed that epitopic suppression did not arise due to nonspecific suppressor phenomena. Coculture experiments demonstrated that epitopic suppression was partially mediated by suppressor T cells which specifically inhibited the anti-hapten but not the anti-carrier antibody response. The majority of these T cells were shown to possess the Lyt-2+ phenotype. Apart from the T suppressor population we demonstrated a deficiency at the B-cell level which contributed to the total suppressive effect. Epitopic suppression, therefore, resulted from the effects of dual specific suppressor mechanisms.