Accessory signals in murine cytolytic T cell responses. Dual requirement for IL-1 and IL-6.

We have examined the nature of the accessory factors required for the development of primary murine CTL in accessory cell-depleted allogeneic mixed lymphocyte cultures. None of the known macrophage-derived factors was active by itself but the combination of IL-1 and IL-6 induced cytolytic responses equivalent to those of unfractionated cultures. Experiments with purified T cell subsets and antibodies blocking the action of IL-2 and IL-4 demonstrated that IL-1 and IL-6 acted directly on CD8+ cells capable of growth factor production. Analysis of the respective roles of IL-1 and IL-6 indicated that IL-6 acts before IL-1 and is capable apparently by itself to induce responsiveness to IL-2. By contrast, production of IL-2 required the additional presence of IL-1.