Concanavalin A induced histamine release from human basophils in vitro

The site of interaction for concanavalin A (Con-A)-induced histamine release from human basophils was studied in vitro. Blocking the epsilon one determinant (D leads to 1) of IgE with high concentrations of monomer (Fab) anti-Depsilon1 does not significantly inhibit the quantity of histamine released by suboptimum concentrations of Fc specific anti-IgE. This indicates that the monomer anti-Depsilon1 does not have the capacity to sterically hinder the bridging of all of the determinants in the Cepsilon3 and Cepsilon4 domains (Fc'-epsilon-region) of IgE. The monomer anti-Depsilon1 does effectively inhibit release induced by suboptimum concentrations of Con-A. The data indicate that for suboptimum concentrations, Con-A activation is IgE mediated and takes place in the proximity of Depsilon1 and not at the membrane receptor for IgE.