Mechanism of adjuvant activity of dental plaque: in vitro activation of residual helper T-cell precursors in T-cell-deficient murine spleen cell cultures.

The immunoenhancing activity of a water-soluble extract of dental plaque (DP), which contains a mixture of microbial antigens, has been investigated. DP was tested for its capacity to augment the in vitro antibody-forming cell (AFC) response to sheep erythrocyte by adherent spleen cells from thymectomized, lethally irradiated, and bone marrow-transplanted (TxB) mice. Although DP was found to induce a small polyclonal AFC response, most of the increase in AFC induced by DP was antigen dependent. The latter enhancing effect is an indicator of the adjuvanticity of DP. This adjuvant activity of DP was T-cell-dependent, since removal of the residual prethymic and/or thymic-derived lymphocytes (T-cells) by anti-T-cell serum (anti-theta) and guinea pig complement abrogated the capacity of DP to augment the in vitro AFC response. This view was further supported by the synergistic restorative effect obtained by culturing anti-theta-treated adherent spleen cells with both DP and a population of unactivated T-cells that by themselves were unable to significantly enhance AFC responsiveness. Moreover, DP was found to be mitogenic for thymocytes. The cumulative results suggest that the adjuvant activity of DP is dependent on both the T- and B-cell-activating components present in DP.