T-CELL LONG-TERM HYPORESPONSIVENESS FOLLOWS ANTIGEN RECEPTOR ENGAGEMENT AND RESULTS FROM DEFECTIVE SIGNAL-TRANSDUCTION

T cell receptor (TCR)-mediated stimulation of T hybridomas leads to ce ll activation and lymphokine production that is followed by a long-ter m hyporesponsiveness. To investigate the biochemical events involved i n the induction and maintenance of this antigen receptor hyporesponsiv eness or anergy, we have expressed a G protein/PLC beta 1-coupled musc arinic subtype 1 acetylcholine receptor in a murine T cell hybrid. Tra nsfected cells were capable of responding to both muscarinic agonists and TCR ligands by inducing interleukin-2 secretion that was sensitive to cyclosporin A and dexamethasone. Both receptors induced tyrosine k inase (TK) activity, but muscarinic stimulation did not affect tyrosin e phosphorylation of PLC gamma 1, nor did the TK inhibitor, herbimycin , block muscarinic receptor-mediated calcium mobilization. These data indicate that in T cells, the muscarinic receptor mediates T cell effe ctor functions by regulating a TK-independent proximal pathway which l ater converges with the TCR pathway. Using these cells, we have explor ed the long-term consequences of T cell stimulation via antigen or mus carinic receptors. Our results show that hyporesponsiveness specifical ly follows TCR engagement and appears to result from a defect in the e arly signal transduction initiated by TCR cross-linking. A study of TC R-mediated signaling supports this model by showing that tyrosine phos phorylation and calcium mobilization are deficient in hyporesponsive T cells.