Responsiveness of T cells to mutant major histocompatibility complex class I antigen. II. Role of stimulator-type accessory cells with reference to interleukin 1 production.

Mechanisms of the activation of T cells responding to major histocompatibility complex (MHC) class I antigen were investigated with special reference to interleukin 1 (IL-1) production from stimulator-type accessory cells. For this purpose, we used mainly fractionated Lyt-2+T cells of C57BL/6 (B6) mice as responder cells and irradiated spleen cells or those deprived of adherent cells of B6.C-H-2bm1 (bm1) mice as stimulator cells. Lyt-2+ T cells of B6 mice proliferated in the presence of irradiated whole spleen cells of bm1 mice but did not to Sephadex G-10 column-passed bm1 spleen cells. The unresponsiveness in the latter case was overcome by the supplement of recombinant IL-1 and/or IL-2 in the culture medium. These interleukins were shown to promote the proliferative response of B6 Lyt-2+ T cells in the presence of stimulator-type T or B cells. Both interleukins also facilitated the generation of cytotoxic T cells from B6 Lyt-2+ cells to H-2Kbm1 antigen in the mixed lymphocyte culture deficient in stimulator-type accessory cells. IL-1 was shown to enhance the expression of IL-2 receptor on the responding Lyt-2+ T cells as assessed by flow cytometry. IL-1 binding to responding T cells were also assayed by means of iodinated IL-1 and was shown to increase significantly on responding Lyt-2+ cells. Overall results indicate that accessory cells might play dual roles in the activation of Lyt-2+ T cells responding to allogeneic MHC class I antigen: direct presentation of the antigen to responder T cells and production of IL-1. Both signals are essentially required for Lyt-2+ T cells responding to allogeneic MHC class I antigen to initiate proliferation and also to differentiate into cytotoxic T cells.