CA2-CELLS GRADUALLY INCREASES WITH PEPTIDE CONCENTRATION (ANALOG SIGNALING)( MOBILIZATION IN PHYSIOLOGICALLY STIMULATED SINGLE T)

We have investigated Ca2+ mobilization in single T cells stimulated wi th their physiological Ligand, i.e. antigenic peptide bound to major h istocompatibility complex (MHC) molecules on antigen-presenting cells (APC). Fibroblasts expressing I-E(d) class II molecules were pulsed wi th a peptide derived from the lambda 2(315) immunoglobulin light chain . Onto such antigen-pulsed fibroblasts were sedimented cloned Th1 cell s loaded with Fura-2. Changes in cytosolic Ca2+ concentration in singl e T cells were continually monitored by use of an imaging system based on fluorometry. Ca2+ mobilization was both peptide-specific and MHC-r estricted. Within seconds of the initial APC-T cell contact, a Ca2+ sp ike could be observed. The Ca2+ response gradually declined over a 25- min period, during which oscillations were noted. Various parameters c haracterizing the magnitude of the Ca2+ response (latency, increase ra te, max and mean Ca2+ increase, frequency and period of oscillations) all correlated with the amount of peptide used for pulsing the fibrobl asts. Thus, Ca2+ mobilization in single T cells appears not to be an a ll or none phenomenon. Rather, activation is incremental (analog signa ling), the degree of Ca2+ mobilization probably being related to the n umber of stimulatory peptide-MHC complexes on the surface of the APC. The extent of calcium mobilization and lymphokine production (interleu kin (IL)-2, IL-3, interferon-gamma) correlated, at least at the popula tion level.