Activation of Rat Basophilic Leukemia Cells by ϵBP, an IgE-Binding Endogenous Lectin

IgE-binding protein (ϵBP) is a β-galactoside-binding animal lectin identified by its affinity for IgE. We have reported that ϵBP also binds the mast cell high-affinity IgE receptor (FcϵRI), via lectin-carbohydrate interaction. We have now studied the physiological significance of ϵBP-IgE-FcϵRI interactions in mast cell activation using rat basophilic leukemia (RBL) cells as the model system. We report here that both unsensitized and IgE-sensitized RBL cells are activated upon exposure to ϵBP-coated surfaces. Activation of RBL cells by the lectin ϵBP can be significantly inhibited by appropriate saccharides. Exposure of RBL cells to ϵBP-coated surfaces caused cell spreading similar to that caused from adherence to fibronectin-coated surfaces. However, ϵBP by itself caused mediator release whereas fibronectin only potentiated antigen-mediated activation of RBL cells. Under appropriate conditions, ϵBP, therefore, has the potential to activate mast cells culminating in augmentation of an inflammatory response.