Antigen Is Required for the Activation of Effector Activities, whereas Interleukin 2 Is Required for the Maintenance of Memory in Ovalbumin-specific, CD8+ Cytotoxic T Lymphocytes

The mechanisms that maintain memory in T cells are not completely understood. We have investigated the role of antigen and interleukin (IL)-2 in the growth and maintenance of CD8+ T cells using a cytolytic T cell line specific for ovalbumin (OVA)257-264 presented by H-2Kb. This line does not secrete IL-4 or IL-2; hence, stimulation with the OVA-transfected EL4 line (E.G7-OVA) does not induce proliferation without addition of exogenous growth factors. Furthermore, this line can be maintained continuously by weekly addition of irradiated, splenic filler cells and IL-2, with or without E.G7-OVA. Although IL-2 induced proliferation of these cytotoxic T lymphocytes (CTLs), production of interferon γ and tumor necrosis factor α required stimulation of the CTL with E.G7-OVA. The kinetics of lymphokine secretion after stimulation by E.G7-OVA were the same whether the CTL had been maintained with or without antigen (Ag). In addition, both CTL lines killed E.G7-OVA target cells within 4 h. Thus, the effector functions of these CTLs were rapidly induced by T cell receptor (TCR) occupancy. CTLs cultured with or without Ag also served as memory T cells when parked for 100 d in unirradiated, syn