Monomeric IgE Stimulates NFAT Translocation Into the Nucleus, a Rise in Cytosol Ca2+, Degranulation, and Membrane Ruffling in the Cultured Rat Basophilic Leukemia-2H3 Mast Cell Line

Abstract

Mast cells are key regulators in allergy and inflammation, and release histamine, cytokines, and other proinflammatory mediators. In the classical view, IgE acts merely to prime mast cells, attaching to FcεRs but not evoking any cell signaling response until cross-linked by the presence of a multivalent allergen. However, several recent studies have reported that IgE alone can promote cell survival and cytokine production in the absence of cross-linking by allergen. In this study we demonstrate that acute addition of monomeric IgE elicits a wide spectrum of responses in the rat basophilic leukemia-2H3 mast cell line, including activation of phospholipases Cγ and D, a rise in cytosol Ca2+, NFAT translocation, degranulation, and membrane ruffling within minutes. Calcium transients persist for hours as long as IgE is present resulting in the maintained translocation of the transcription factor NFAT to the nucleus. Removal of IgE reverses the signaling processes. Our results indicate that, far from simply preparing the cells for a response to allergen, monomeric IgE can stimulate signaling pathways that lead to degranulation, membrane ruffling, and NFAT translocation. The mechanism of activation is likely to be via aggregation of the FcεR1 because activation by IgE can be inhibited with monovalent hapten.

Cutting Edge: Death of a Dogma or Enforcing the Artificial: Monomeric IgE Binding May Initiate Mast Cell Response by Inducing Its Receptor Aggregation

“…An important insight into the events induced upon mIgE binding was that addition of monovalent haptens (for which the mIgE used is specific) abrogated the cells' responses (4,8,14). This additionally supported the intriguing possibility that Fc⑀RI-bound mIgEs may undergo aggregation by binding to their Ag recognition site of an epitope on their own structure or of another cell surface component.…”

“…IgE binding was generally considered to just endow the Fc⑀RI with specific Ag recognition capacity or affect its cell surface expression levels. However, this model has been challenged recently by a series of reports suggesting that monomeric IgE (mIgE) 2 binding to the Fc⑀RI does initiate its stimulus-response cascade, resulting in several important cellular activities (3)(4)(5)(6)(7)(8). The first two independent studies (3,4) reported that mIgE binding prolonged survival of mouse mast cells under growth factor-limiting conditions.…”

“…In contrast, Asai et al (3) did not detect any signaling events or significant cytokine secretion. Several more recent articles attracted additional interest as they reported that mIgE binding even induces secretion of granule-stored mediators by the rat mast cells of the RBL-2H3 line, as well as by bone marrow-derived cultured mast cells (BMCMCs) (7,8). Moreover, Kitaura et al (5,6) reported that binding of different monoclonal mIgE induces a spectrum of cell activation events that varied widely depending on the particular IgE mAb used and provided some evidence that these events are a result of Fc⑀RI aggregation.…”

Protective Role of STAT6 in Basophil-Dependent Prurigo-like Allergic Skin Inflammation

“…Supernatants were precipitated with 55% saturated ammonium sulfate and dialyzed in PBS. Monomeric IgE was prepared by removing aggregates by ultracentrifugation at 60,000 3 g for 1 h at 4˚C (28).…”

Negative Signaling in Fc Receptor Complexes

“…An exposure of mast cells to IgE in the absence of antigen was indeed reported 1) to up-regulate the expression of membrane FcεRI (Hsu and MacGlashan, 1996;MacGlashan et al, 1997), 2) to increase the survival of mast cells in the absence of growth factors (Asai et al, 2001;Kawakami and Galli, 2002), and 3) to induce cytokine secretion (Kalesnikoff et al, 2001;Pandey et al, 2004;Kohno et al, 2005). The effect of monomeric IgE on mast cell survival and cytokine secretion was found to depend on the FcRγ ITAM (Kohno et al, 2005), but not the up-regulation of FcεRI expression.…”