Abstract
After specific activation, CD8+ cytotoxic T lymphocytes (CTLs) enter a refractory state termed activation-induced nonresponsiveness (AINR) that is characterized by the inability of T cells to respond to a secondary stimulus. Here, we show that T cell receptor triggering results in rapid degradation of the src-family protein kinase lck through a mechanism that is proteasome- and lysosome-independent, sensitive to cysteine protease inhibitors, and distinct from the pathways involved in degradation of ZAP-70 kinase or zeta-chain of the CD3 complex. Pharmacologic blockade of lck degradation, as well as transfection of refractory cells with an lck expression vector, increased responsiveness of CTLs to repeated antigenic challenge. The development or maintenance of AINR was not affected by exogenously added IL-2, whereas IL-15 or IFN-alpha restored both lck expression and responsiveness of preactivated CTLs. Our results suggest that lck degradation plays an important role in the development of AINR in human CTLs and that this condition can be reverted by pharmacologic agents or lymphokines that prevent lck degradation or induce its expression.