Cross-linking of IgE-receptor complexes by rigid bivalent antigens >200 Å in length triggers cellular degranulation

Abstract

We have examined the effect of cross-linking IgE-receptor complexes with variable receptor-receptor distances on the transmembrane signaling that leads to degranulation of rat basophilic leukemia cells. Linear polymers of the biotin-binding protein avidin were generated with bis biotin-1,12-diamidododecane, and a dinitrophenyl-biotin conjugate was bound at each end of the polymers to form a series of rigid bivalent haptens of well-defined length. The polymers were fractionated by size with nondenaturing PAGE, electroeluted, and tested for their ability to stimulate degranulation of rat basophilic leukemia cells sensitized with anti-DNP IgE. We found that hexamers of avidin (of length ≥240 Å) were as effective in triggering degranulation as dimers (of length ~80 Å), while the monomeric avidin antigen (of length ~40 Å) elicited a poorer degranulation response from the cells. The mechanism by which aggregation of cell surface receptors can initiate signal transduction is discussed in light of these results.