Functional and biochemical characterization of a calcium-ionophore-induced state of unresponsiveness in a cytolytic T cell clone. |
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Authors: | G Trenn J Sykora M C Michel G Brittinger |
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Institution: | Division of Hematology, University of Essen, Germany. |
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Abstract: | To characterize the requirements for the induction of an anergic state in immunocompetent cells we examined the effect of an increase in intracellular calcium concentration on the subsequent responsiveness of cytolytic T cells to antigenic stimulation in vitro. Pretreatment of a murine cytolytic T cell clone with the calcium-ionophore A23187 resulted in the induction of an anergic state characterized by a decrease in cytolytic activity and granule exocytosis upon Ag-specific stimulation. Furthermore, IFN-gamma synthesis declined whereas de novo synthesis of a yet unidentified protein with a molecular mass of 33 kDa as well as proliferative response of cells in response to exogenous IL-2 were unaffected. This state of partial unresponsiveness 1) could be prevented by concomitant pretreatment of cells with cyclosporin A or protein synthesis inhibitors and 2) was reversible within 48 h. Biochemical analysis of TCR-induced intracellular activation revealed a block in signal transduction before the activation of protein kinase C because cellular unresponsiveness could be bypassed by the phorbol ester PMA plus the calcium-ionophore A23187. However, phosphatidylinositol turnover was markedly inhibited in unresponsive cells that also did not show a calcium influx on stimulation with concanavalin A. We conclude that a rise in intracellular calcium in cytolytic T cells might not only be necessary for cellular activation but may also trigger the induction of a partial unresponsiveness to antigenic stimulation due to an inhibition in the early phase of signal transduction. |
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