Cross-linking of IgE-receptor complexes by rigid bivalent antigens greater than 200 A in length triggers cellular degranulation

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, electro-eluted, 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 greater than or equal to 240 A) were as effective in triggering degranulation as dimers (of length approximately 80 A), while the monomeric avidin antigen (of length approximately 40 A) 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.