Activation of Rat Basophilic Leukemia Cells by ε{lunate}BP, an IgE-Binding Endogenous Lectin

IgE-binding protein (ε{lunate}BP) is a β-galactoside-binding animal lectin identified by its affinity for IgE. We have reported that ε{lunate}BP also binds the mast cell high-affinity IgE receptor (Fcε{lunate}RI), via lectin-carbohydrate interaction. We have now studied the physiological significance of ε{lunate}BP-IgE-Fcε{lunate}RI 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 ε{lunate}BP-coated surfaces. Activation of RBL cells by the lectin ε{lunate}BP can be significantly inhibited by appropriate saccharides. Exposure of RBL cells to ε{lunate}BP-coated surfaces caused cell spreading similar to that caused from adherence to fibronectin-coated surfaces. However, ε{lunate}BP by itself caused mediator release whereas fibronectin only potentiated antigen-mediated activation of RBL cells. Under appropriate conditions, ε{lunate}BP, therefore, has the potential to activate mast cells culminating in augmentation of an inflammatory response.