THE CALCIUM CURRENT ACTIVATED BY T-CELL RECEPTOR AND STORE DEPLETION IN HUMAN-LYMPHOCYTES IS ABSENT IN A PRIMARY IMMUNODEFICIENCY

Stimulation of antigen receptors of lymphocytes triggers a transitory release of Ca2+ from internal stores and the opening of a transmembran e Ca2+ conductive pathway, The latter underlies the sustained increase of intracellular free calcium concentration, and it seems to be a key event in the Ca2+-dependent biochemical cascade leading to T cell pro liferation, Alternatively, pharmacological depletion of internal store s by itself activates Ca2+ influx, This has led to the hypothesis that antigen-triggered Ca2+ influx is secondary to Ca2+ release from inter nal stores, However, the precise relationship between antigen and Ca2 release-activated Ca2+ currents remains unclear, particularly since n either of them has been electrophysiologically recorded in normal lymp hocytes. Using the whole-cell and the perforated configurations of the patch clamp technique on peripheral blood lymphocytes, we found that a law amplitude Ca2+-selective current was triggered when intracellula r stores were depleted by stimuli such as the intracellular perfusion of inositol triphosphate or thapsigargin and the extracellular perfusi on of ionomycin, A similar current was elicited by the cross-linking o f the T cell receptor-CD3 complex, This current displayed an inward re ctification below 0 mV and was completely blocked by the divalent cati on Cd2+, It was very selective for Ca2+ over Na+ and insensitive to ch anges in chloride concentration, The physiological relevance of this c onductance was investigated with the analysis of abnormal Ca2+ signali ng in lymphocytes from a patient suffering from a primary immunodefici ency associated with a defective T cell proliferation Using fura-2 vid eo imaging, an absence of Ca2+ influx was established in the patient's lymphocytes, whereas the Ca2+ release from internal stores was normal , This was the case whether cells were stimulated physiologically thro ugh their antigen receptors or with store depleting pharmacological ag ents, Most importantly, no Ca2+-selective current was elicited in thes e cells, Our data strongly suggest that the Ca2+ release-activated cur rent underlies the sustained Ca2+ influx during antigenic stimulation and that it plays a key role in the immune function.