Suppression of antigraft immunity by preimmunization. V. Characterization of suppressor T memory cells

We have previously shown that after intravenous (i.v.) immunization of mice with allogeneic spleen cells, two populations of suppressor T (Ts) cells may occur that can suppress delayed-type hypersensitivity (DTH) to alloantigens: Ts effector cells that transiently occur in the spleen, and long-lived, recirculating Ts cells that occur in thoracic duct lymph and can be transferred by parabiosis. In this study, we investigated whether the latter Ts cells fulfill the criteria for memory T lymphocytes, such as induction by doses of antigen lower than required for T effector cell induction, accelerated onset of activity after reactivation and an increased activity as compared with virgin T cells. The Ts cells accounting for the long-lasting state of suppression of DTH to alloantigens indeed fulfilled these criteria. These Ts memory cells displayed the Thy-1+, L3T4-, Lyt-1+2+ phenotype.