Early steps of lymphocyte activation bypassed by synergy between calcium ionophores and phorbol ester

Abstract

Although it has been proposed that the activation of T lymphocytes is mediated by an early rise in cytosolic calcium concentration, it has not been possible to mimic antigen- or mitogen-induced mouse lymphocyte activation by calcium ionophores that bypass receptor-mediated processes. There is now evidence from other systems that the rise in cytosolic calcium which follows receptor triggering is preceded by the breakdown of phosphatidylinositol bisphosphate into 1,2-diacylglycerol and inositol trisphosphate. The latter is known to cause release of calcium from intracellular stores. The cellular target for the former is now widely accepted to be protein kinase C. Therefore, ligand-induced cellular response follows a rise in cytosolic calcium concentration and protein kinase C activation. Here we confirm that the calcium ionophores A23187 and ionomycin do not activate mouse T lymphocytes. However, either one in combination with the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA), which is structurally related to 1,2-diacylglycerol, induces in lymphoid cell populations the expression of receptors for interleukin-2 (IL-2), the secretion of IL-2 and cell proliferation as measured by 3H-thymidine uptake. The growth-promoting effect of IL-2 on an exogenous IL-2-dependent clone could not be substituted for by ionomycin either alone or with TPA. Thus, the combination of calcium ionophores and TPA bypasses the requirement for antigen- or lectin-induced signal at the onset of lymphocyte activation.

Variation in the Cd3ζ (Cd247) Gene Correlates with Altered T Cell Activation and Is Associated with Autoimmune Diabetes

“…Activated T cells of NOD origin were reported to express higher levels of ICOS (32). Although Ctex constitutes the major locus involved in the control of CTLA-4 expression, we observed that this locus does not influences ICOS protein expression in NOD mice (Supplemental Fig.…”

“…5D, 5E). As shown in The phorbol ester PMA and the calcium ionophore ionomycin fully trigger activation of T cells, bypassing the cross-linking of the TCR/CD3 complex (32). Therefore, we reasoned that the addition of PMA plus ionomycin should improve the impaired T cell activation observed in NOD T cells if it was conferred by the NOD allele of Cd3z.…”

Inhibitors of arachidonic acid lipoxygenase impair the stimulation of inositol phospholipid hydrolysis by the T lymphocyte mitogen phytohaemagglutinin

“…DAG stimulates protein kinase C whereas IP3 mediates elevation of cellular Ca2+ concentrations [3]. Cascades of biochemical processes consequent to these early events eventually synergize in securing commitment of the lymphocyte to mitosis [4].…”

B Cell Receptor Basal Signaling Regulates Antigen-Induced Ig Light Chain Rearrangements

“…52 and 53), and ionomycin, a calcium ionophore that activates downstream calcium-dependent signaling pathways (54). Combinations of PMA and ionomycin have long been used to initiate activation signals in lymphocytes (55,56).…”