Signaling Alterations in Activation-Induced Nonresponsive CD8 T Cells

Abstract

Costimulation-dependent production and autocrine use of IL-2 by activated CD8 T cells results in initial clonal expansion, but this is transient. The cells quickly become anergic, unable to produce IL-2 in response to Ag and costimulation, irrespective of the form of costimulation. This activation-induced non-responsiveness (AINR) differs from “classical” anergy in that it results despite the cells receiving both signal 1 and signal 2. AINR cells can still proliferate in response to exogenous IL-2, but can no longer produce it. Other TCR-mediated events including cytolytic function and IFN-γ production are not affected in the AINR state. To characterize the mechanism(s) responsible for lack of IL-2 production in CD8 T cells in the AINR state, microspheres bearing immobilized anti-TCR Abs or peptide-MHC complexes, B7-1, and ICAM-1 were used to provide well-defined stimuli to the cells. Comparison of normal and AINR cells revealed that in AINR cells extracellular signal-regulated kinase (ERK) is upregulated more transiently, Janus kinase activation is substantially reduced, and activation of p38 is eliminated. PMA and ionomycin restored proliferation and IL-2 production in AINR cells, indicating a signaling defect upstream of Ras and protein kinase C. Inhibitors of ERK (PD98059) and of p38 kinase (SB202190) blocked IL-2 mRNA expression and proliferation of both peptide-MHC/B7-1/ICAM-1-stimulated normal cells and PMA/ionomycin-stimulated AINR cells. Together these results demonstrate that activation of at least ERK and p38 is essential for IL-2 production by CD8 T cells and that up-regulation of these mitogen-activated protein kinases, along with Janus kinase, is defective in AINR cells.

Galectin-1 Tunes TCR Binding and Signal Transduction to Regulate CD8 Burst Size

“…The addition of exogenous IL-2 can reverse AINR, which has been characterized to result from impaired TCR-induced MAPK activation (including ERK) and IL-2 production (47)(48)(49). We found that cultures of stimulated gal-1-deficient CD8 cells produce more IL-2 than their wild-type counterparts.…”

“…Previous studies by Mescher and colleagues (47)(48)(49) have identified a period of activation-induced nonresponsiveness (AINR) in CD8 T cells 2-4 days after initial TCR engagement, wherein CD8 T cells become unable to produce IL-2 or proliferate in response to secondary TCR engagement. The addition of exogenous IL-2 can reverse AINR, which has been characterized to result from impaired TCR-induced MAPK activation (including ERK) and IL-2 production (47)(48)(49).…”

Molecular basis for checkpoints in the CD8 T cell response: Tolerance versus activation

“…Defects in activation of all three of these MAPKs were seen in AINR CD8 T cells [68]. Initial activation of ERK (1 min) was comparable in normal and AINR cells, but activity declined much more rapidly in AINR cells.…”

“…Treatment of AINR cells with phorbol myristic acetate (PMA), an activator of ras and PKC, and ionomycin, a calcium ionophore, activated ERK, JNK and p38 and stimulated IL-2 production and proliferation by the cells, and the proliferation was inhibited by ERK and p38 inhibitors [68]. These results suggest that cells in the AINR state are unable to activate p21 ras via TCR and CD28 signaling, although this has not yet been directly demonstrated.…”

“…Signaling in naïve and AINR CD8 T cells was studied in vitro using artificial APC having just peptide-MHC Ag complex or anti-TCR mAb immobilized alone on microspheres to provide signal 1, or along with immobilized B7-1 to provide signals 1 and 2 [68]. ERK was activated in response to just TCR engagement, and activation was increased little, if at all, when B7-1 was present (Fig.…”