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J. Exp. Med.,
Volume 187, Number 1, January 5, 1998 49-57
By
From the Departments of Ophthalmology, Pathology, and the Winship Cancer Center, Emory
University School of Medicine, Atlanta, GA 30322
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
and tumor necrosis factor
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, syngeneic recipients without OVA. In the absence of OVA, the precursor frequency was identical in spleens of normal and
2-microglobulin knockout recipients, but
significantly less in IL-2 knockout mice. The decline of memory in the absence of IL-2 supports data from other investigators, suggesting that cell cycling is important to the maintenance
of CD8+ T cell memory. These data also suggest that stimulation of OVA-specific CTLs by
lymphokines seems to be more important to maintaining memory than stimulation of TCRs
by cross-reactive peptides complexed to class I molecules.
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