Membrane IgE Binds and Activates FcεRI in an Antigen-Independent Manner

Abstract

Interaction of secretory IgE with FcεRI is the prerequisite for allergen-driven cellular responses, fundamental events in immediate and chronic allergic manifestations. Previous studies reported the binding of soluble FcεRIα to membrane IgE exposed on B cells. In this study, the functional interaction between human membrane IgE and human FcεRI is presented. Four different IgE versions were expressed in mouse B cell lines, namely: a truncation at the Cε2-Cε3 junction of membrane IgE isoform long, membrane IgE isoform long (without Igα/Igβ BCR accessory proteins), and both εBCRs (containing membrane IgE isoforms short and long). All membrane IgE versions activated a rat basophilic leukemia cell line transfected with human FcεRI, as detected by measuring the release of both preformed and newly synthesized mediators. The interaction led also to Ca2+ responses in the basophil cell line, while membrane IgE-FcεRI complexes were detected by immunoprecipitation. FcεRI activation by membrane IgE occurs in an Ag-independent manner. Noteworthily, human peripheral blood basophils and monocytes also were activated upon contact with cells bearing membrane IgE. In humans, the presence of FcεRI in several cellular entities suggests a possible membrane IgE-FcεRI-driven cell-cell dialogue, with likely implications for IgE homeostasis in physiology and pathology.

Antitumor IgE Adjuvanticity: Key Role of FcεRI

“…1B). When IgE-loaded tumor cells were incubated with the rat basophilic cell line RBL-2H3, expressing FcRI, degranulation and mediator release were triggered via FcRI cross-linking, as previously reported for membrane IgE (30). IgE on tumor cells induced a ␤-hexosaminidase release Ͼ60% of the maximum release obtained upon cell lysis with Triton X-100.…”

“…Overall, this work embodies a major step forward in the development of an IgE-based cellular vaccine, together with a better understanding of the in vivo importance of FcRI involvement. The exploitation of the knowledge on the IgE-FcRI interaction (1,30,42,48), together with the experimental systems established in this study, should allow further progress in the application of IgE adjuvanticity. The proof of principle that surface IgE is a powerful adjuvant in antitumor immunity has been established.…”

“…Human IgE loading was conducted incubating tumor cells with NIP-OSu (4-hydroxy-5-iodo-3-nitrophenylacetyl-hydroxysuccinimidyl ester; Cambridge Research Biochemicals), 0.2 mg/10 6 cells in 10 mM sodium phosphate (pH 7.2) (10 6 cells/ml) for 45 min at room temperature. Following a 10 min blocking reaction with RPMI 1640 medium supplemented with 10% FCS and washing, cells were incubated 45 min at 4°C in PBS containing 5% BSA with 20 g/ml purified chimeric anti-NIP (4-hydroxy-5-iodo-3-nitrophenylacetyl) human IgE mAb secreted by a stably transfected J558L cell clone, as previously reported (30).…”

The Extracellular Membrane-Proximal Domain of Human Membrane IgE Controls Apoptotic Signaling of the B Cell Receptor in the Mature B Cell Line A20

“…Also, for the -isotype, signal transduction was proposed to be different from other isotypes, including interactions of the cytoplasmic tail with specific cellular proteins (6,32). Moreover, it was recently reported that IgE ϩ cells could directly interact and trigger degranulation, in an Ag-independent manner, with mast cell and basophils expressing the FcRI (33).…”

Cutting Edge: IgE Plays an Active Role in Tumor Immunosurveillance in Mice

“…Although we failed to isolate tumor-specific hybridomas from either spleen or bone marrow of KN1 mice that rejected the tumors, we produced evidence of the existence of tumor-reactive IgE by a functional assay we previously developed (18). N2C cells were incubated with sera from tumor-challenged WT, FceRIa-KO, KN1, and DM mice and mixed with RBL-2H3 rat basophilic leukemia cells.…”