Class I restricted interaction between suppressor and cytolytic cells in the response to minor histocompatibility antigens

Inoculation of 10⁸ unirradiated, minor H antigen incompatible spleen cells into recipients leads to a failure of the induction of cytolytic T lymphocytes (CTL) specific for these antigens. In contrast, a strong CTL response against minor H antigens is obtained when the inoculated cells are irradiated or treated with Thy-1-, Lyt-1- or Lyt-2-specific antibody and complement. Thus the failure of CTL induction is probably due to suppression mediated by radiosensitive, Lyt-1⁺2⁺ T cells in the immunizing inoculum. We demonstrate here that the inoculated cells must share class I MHC loci with the recipients for the suppression to occur. Thus, the interaction between the suppressor T (Ts) cells and their targets (presumably the CTL precursors) is restricted by class I molecules. A disparity at class II loci between the inoculated cells and the recipients overrides the class I-restricted suppression, possibly through a positive allogeneic effect. The simplest interpretation of the class I restriction of Ts cell-target cell interaction is that the CTL precursors recognize minor H antigens in the context of class I molecules on the surface of the Ts cells themselves.