Relationship of IgE receptor topography to secretion in RBL-2H3- mast cells

In RBL-2H3 rat leukemic mast cells, cross-linking IgE-receptor complexes with anti-lgE antibody leads to degranulation. Receptor cross-linking also stimulates the redistribution of receptors on the cell surface, a process observed here by labeling the anti-lgE with 15 nm protein A-gold particles that are visible by back-scattered electron imaging in the scanning electron microscope. We report that anti-lgE binding stimulates the redistribution of IgE-receptor complexes at 37°C from a dispersed topography to distributions dominated sequentially by short chains, small clusters, and large aggregates of cross-linked receptors. Cells incubated with 1 μg/ml anti-IgE, a concentration that stimulates maximum net secretion, redistribute receptors into chains and small clusters during a 15 min incubation period. At 3 and 10 μg/ml anti-IgE, net secretion is reduced and the majority of receptors redistribute rapidly into clusters and large aggregates. The addition of Fab fragments with the high anti-IgE concentrations, to reduce cross-linking, delays receptor aggregation and enhances secretion. The progression of receptors from small clusters to large aggregates is prevented in cells treated with dihydrocytochalasin B to prevent F-actin assembly. These results establish that characteristic patterns of receptor topography are correlated with receptor activity. In particular, they link the formation of large receptor aggregates to reduced signalling activity. Cytoskeleton-membrane interaction is implicated in the formation or stabilization of the large receptor clusters.