Genetic and stimulator cell requirements for generation and activation of minor histocompatibility antigen-specific memory cytotoxic T-lymphocyte precursors

By adding IL-2 (supernatant of culture of concanavalin A-activated rat spleen cells) on Day 3 of mixed leucocyte cultures (MLC) we managed to fully activate multiple minor histocompatibility antigen (MIHA)-specific cytotoxic T-lymphocyte precursors (CTLp). In this newly developed system we studied genetic and stimulator cell requirements for the generation and activation of MIHA-specific memory CTLp. Memory CTLp were activated to generate effector CTL in MLC only when major histocompatibility complex (MHC)-compatible MIHA-allogeneic cells were used as stimulators. In contrast, memory CTLp were generated in mice that were primed by injection of either MHC-compatible or incompatible MIHA-allogeneic spleen cells. A surprisingly small number (10⁴) of MHC-disparate cells cross-primed mice effectively. For priming, no special accessory cell types were required as stimulators, and 10⁴ adherent cell-depleted spleen cells primed mice as well. These results contrasted to another finding that sonication-disrupted 10⁶ stimulator cells did not prime mice effectively, and antigens shed from 10⁷ live stimulator cells failed to sensitize host antigen-presenting cells for priming. It is suggested from these results that the mode of recognition of MIHA by virgin CTLp is unique or that an as yet unknown unusual stimulation pathway works for the priming.