Ability of pure resting CD8+ human T cells to respond to alloantigen.

The ability of highly purified resting human CD8 cells to respond to alloantigens in vitro was examined. Necessary conditions for induction of interleukin 2 receptors (IL-2R), IL-2 production, proliferative responses, and various effector functions were determined. Allogeneic non-T cells induced IL-2R expression in a high proportion of resting CD4 and CD8 cells, but only CD4 cells produced detectable amounts of IL-2. CD8 cells also became IL-2 responsive upon stimulation with purified resting allogeneic CD4 or CD8 cells, indicating that HLA class I+, II- cells alone may initiate activation of resting CD8 cells. The activated CD8 cells needed the presence of simultaneously activated CD4 cells or exogenous IL-2 to be able to synthesize DNA. Effector functions like cytotoxicity, mixed lymphocyte culture (MLC) suppression, or gamma interferon (IFN-gamma) production were also only detectable when the CD8 cells were activated in the presence of IL-2.