Distinct aggregation of β- and γ-chains of the high-affinity IgE receptor on cross-linking

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