Biochemical Events Involved in IgE-Dependent Mediator Release

Abstract

Biochemical events involved in IgE-dependent mediator release were analyzed using rat peritoneal mast cells, IL-3-dependent mouse mast cell line PT-18 cells, bone marrow-derived mouse mast cells, and cultured human basophils. The results revealed that bridging of IgE receptors initiates activation of a variety of membrane-associated enzymes, such as serine protease, phospholipase C, methyltransferases, and adenylate cyclase, resulting in the stimulation of phosphatidylinositol (PI) turnover, and a transient increase in phospholipid methylation and intracellular cAMP. Mobilization of intracellular Ca2+ was detected by Quin-2 fluorescence within 5 sec after antigen challenge. Stimulation of PI turnover results in an accumulation of 1,2-diacylglycerol (DAG) in the plasma membrane and the release of inositol triphosphate (IP3) into the cytoplasm. IP3 triggers mobilization of intracellular Ca2+, and DAG in turn activates protein kinase C. An increase in intracellular cAMP activates cAMP-dependent protein kinase. Evidence was obtained that GTP-binding protein is not involved in the transduction of IgE-mediated triggering signals for mediator release. Although the sequence of enzymes activated by receptor bridging is not clear, the results suggest that the mobilization of intracellular Ca2+ and PI turnover play a central role in the biochemical cascade involved in the IgE-dependent mediator release from mast cells and basophils.