Insights into immunoglobulin E receptor signaling from structurally defined ligands.
The asymmetrical structure of bent immunoglobulin E (IgE) bound to its high-affinity receptor, Fc epsilon RI, suggests a possible role for this configuration in the regulation of signaling mediated by cross-linking of Fc epsilon RI on the surface of mast cells and basophils. Indeed, the presence of bound IgE strongly influences the capacity of cross-linked Fc epsilon RI dimers to trigger mast cell degranulation, implicating orientational constraints by bound IgE. Bivalent ligands that cross-link by binding to bivalent IgE can form linear and cyclic chains of IgE/Fc epsilon RI complexes, and these exhibit only limited capacity to stimulate downstream signaling and degranulation, whereas structurally analogous trivalent ligands, which can form branched networks of cross-linked IgE/Fc epsilon RI complexes, are more effective at cell activation. Long bivalent ligands with flexible spacers can form intramolecular cross-links with IgE, and these stable 1:1 complexes are very potent inhibitors of mast cell degranulation stimulated by multivalent antigen. In contrast, trivalent ligands with rigid double-stranded DNA spacers effectively stimulate degranulation responses in a length-dependent manner, providing direct evidence for receptor transphosphorylation as a key step in the mechanism of signaling by Fc epsilon RI. Thus, studies with chemically defined oligovalent ligands show important features of IgE receptor cross-linking that regulate signaling, leading to mast cell activation.
Holowka
David
D
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853-1301, USA. dah24@cornell.edu
Sil
Dwaipayan
D
Torigoe
Chikako
C
Baird
Barbara
B
D000818:Animals; D004247:DNA / Q000737:chemistry / Q000276:immunology; D006801:Humans; D007073:Immunoglobulin E / Q000276:immunology*; D008024:Ligands; D017455:Receptors, IgE / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000276:immunology*; D015398:Signal Transduction
D008024:Ligands; D017455:Receptors, IgE; D007073:Immunoglobulin E; D004247:DNA