T cell receptor reconstitution fails to restore responses of T cells rendered hyporesponsive by tumor necrosis factor

Expression and function of the antigen T cell receptor (TCR) play a central role in regulating immune responsiveness. Accordingly, targeting the expression of TCR or its associated CD3 subunits profoundly influences T cell development and adaptive immunity. Down-regulation of the invariant TCR chain has been documented in a wide variety of chronic inflammatory and infectious diseases, and is thought to contribute to the paradoxical immune suppression observed in these diseases. Previously, we reported that prolonged exposure of T cell hybridoma clones to tumor necrosis factor (TNF) induces nondeletional and reversible hyporesponsiveness to TCR engagement, associated with down-regulation of TCR chain expression, impaired TCR CD3 complex assembly, and attenuation of TCR-induced membrane proximal tyrosine phosphorylation. Here, we have tested whether receptor specific T cell responses are rescued in TNF-treated T cell hybridomas by retroviral-mediated expression of -chimeric (C2 ) receptors or wildtype TCR . Expression of C2 receptors at the cell surface is relatively refractory to chronic TNF stimulation. However, C2 receptor function depends on association with endogenous TCR chains, whose expression is down-regulated by TNF, and so C2 receptor specific responses are attenuated in TNF-treated T cells. Unexpectedly, overexpression of wild-type TCR maintains cell surface TCR CD3 complex expression but fails to rescue receptor proximal signaling in TNF-treated T cells, suggesting the existence of hitherto unrecognized mechanisms through which TNF regulates T cell responsiveness. We provide additional evidence that TNF also uncouples distal TCR signaling pathways independently of its effects on TCR expression.