Helper Cells in Vitro

The cellular immune reactions to hapten-protein conjugates (in the generation of hapten-specific primary and secondary humoral responses) display a significant dependence upon carrier recognition (reviewed in reference 1). Experimental models, particularly the adoptive transfer of immunocompetent cells into irradiated hosts (2-5), have established that the cooperative interactions involved require a thymus-derived (T) lymphocyte (6) with specificity for the carrier protein (7-9) to induce an optimal response by hapten-primed, antibody-forming precursors (B cells). In vivo methods for generating carrier-reactive T-helper cells include preimmunization with free carrier before immunization with hapten-carrier conjugate (10, 11), adoptive transfer of carrier primed cells (6-9), and the use of thymus-derived cells obtained from spleens of irradiated mice injected with thymocytes and carrier (12-14). These cells, or products derived from them, have been analyzed in vlvo (12-15) and in vitro (16-18) The critical role of the macrophage in a variety of T-cell responses (19-25) suggests that an in vitro system in which macrophage-thymocyte synergy is used might be devised for generating carrier-reactive T cells. Cultured, adherent cells have been shown to substantially preserve thymocyte viability and function in vitro (26), and have been used to selectively enrich antigen-reactive T cells from mice primed in vivo (27). Until recently it has not been possible to generate carrmr-reactive T-helper cells in vitro. In 1973, Kontianen and Feldmann (28) reported the induction of carrier-specific helper T cells in vitro by using spleen and lymph node cells as a source of unprimed T cells. Subsequently, Erb and Feldmann (29-31) have obtained evidence that interaction between macrophages and T cells is essential to the generation of carrier-specific T-helper cells. A detailed examination of the cellular requirements, antigen specificity, or mode of action of T-helper cells generated in wtro has not been reported.