EPSILON-BP, A BETA-GALACTOSIDE-BINDING ANIMAL LECTIN, RECOGNIZES IGE RECEPTOR (FC-EPSILON-RI) AND ACTIVATES MAST-CELLS

IgE-binding protein (epsilonBP) was originally identified in rat basop hilic leukemia (RBL) cells by virtue of its affinity for IgE. EpsilonB P is now known to be a beta-galactoside-binding lectin containing an S -type carbohydrate recognition domain. It is identical to a macrophage surface antigen, Mac-2, and lectins designated as CBP35, L-34, and RL -29, for which various functions have been suggested. Studies from oth er groups as well as ours have indicated that epsilonBP is secreted by cells such as macrophages and is present in extracellular fluids. We demonstrated previously that binding sites for epsilonBP are present o n the surface of RBL cells. In this report, we show that epsilonBP bin ds to a small number of glycoprotein species on the surface of RBL cel ls. Significantly, one of these glycoproteins is the high-affinity IgE receptor (FcepsilonRI). Preliminary studies showed that epsilonBP cau ses mediator release from RBL cells, possibly through cross-linking of FcepsilonRI. The results suggest a function of epsilonBP as an activa tor of mast cells.