Distinct Aggregation of β- and γ-Chains of the High-affinity IgE Receptor on Cross-Linking

Abstract

The high-affinity IgE receptor (Fc∊RI) on mast cells and basophils consists of a ligand-binding α-chain and two kinds of signaling chains, a β-chain and disulfide-linked homodimeric γ-chains. Crosslinking by multivalent antigen results in the aggregation of the bound IgE/α-chain complexes at the cell surface, triggering cell activation, and subsequent internalization through coated pits. However, the precise topographical alterations of the signaling β- and γ-chains during stimulation remain unclarified despite their importance in ligand binding/signaling coupling. Here we describe the dynamics of Fc∊RI subunit distribution in rat basophilic leukemia cells during stimulation as revealed by immunofluorescence and immunogold electron microscopy. Immunolocalization of β- and γ-chains was homogeneously distributed on the cell surfaces before stimulation, while crosslinking with multivalent antigen, which elicited optimal degranulation, caused a distinct aggregation of these signaling chains on the cell membrane. Moreover, only γ- but not β-chains were aggregated during the stimulation that evoked suboptimal secretion. These findings suggest that high-affinity IgE receptor β- and γ-chains do not co-aggregate but for the most part form homogenous aggregates of β-chains or γ-chains after crosslinking.