The Requirement of Ia-Positive Accessory Cells for the Induction of Hapten-Reactive Cytotoxic T Lymphocytes in vitro

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Abstract
The antigen-presenting mechanism to hapten-reactive cytotoxic T cells was studied by using fractionated responder T cells, hapten-modified syngeneic stimulator cells, and accessory cells. When the effect of various treatments on the stimulatory activity by spleen cells in the induction of cytotoxic T cells was studied by coculturing TNP-modified spleen cells and nylon wool column-purified T cells, the stimulatory activity was associated with the spleen cell population adhering to plastic dishes, Sephadex G-10, and nylon wool, and was sensitive to anti-Ia serum and complement treatment. The activity was resistant to anti-Th B serum and anti-Thy 1 serum and complement treatment. In order to figure out the role of Ia antigens for induction of cytotoxic T cells, Ia-negative tumor cells were used as stimulator cells with TNP-modification, and the effect of addition of spleen cells containing Ia-positive cells to the system was studied. The addition of accessory cells restored the induction of TNP-reactive cytotoxic T cell activity under conditions in which the TNP-modified tumor cells alone could not induce cytotoxic T cells to stimulate nylon wool column-purified T cells. In this system, not only syngeneic but also allogeneic spleen cells had the accessory activity. Anti-Ia serum could inhibit the induction of cytotoxic T cells when added continuously to the culture, and this inhibition was specific for the accessory cells added, but not for the responder T cells or stimulator cells. Thus, Ia-positive accessory cells seem to play a crucial role in the induction of cytotoxic T cells in vitro. The possible role of Ia-positive accessory cells is discussed in the context of cellular interactions in the antigen-recognition mechanism of cytotoxic T cells.