THE RECEPTOR WITH HIGH-AFFINITY FOR IGE ON RAT MAST-CELLS IS A FUNCTIONAL RECEPTOR FOR RAT IGG2A

Rat mast cells express high-affinity receptors for IgE (Fc epsilon RI) and low-affinity receptors for IgG (Fc gamma R). In this study, the c apacity of Ige to activate the rat basophilic leukemia (RBL-2H3) and r at peritoneal mast cells was investigated. Immune complexes formed wit h purified rat IgG and antigen as well as chemically cross-linked rat IgG induced histamine release from RBL-2H3 cells. This stimulation was inhibited by pre-incubation of the cells with saturating concentratio ns of monomeric IgE. With chemically cross-linked rat IgG of each subc lass, only IgG2a stimulated histamine release from RBL-2H3 cells and t his release was also inhibited by prior saturation of the Fc epsilon R I with monomeric IgE. Identical results were obtained with rat periton eal mast cells. In binding experiments, IgE and cross-linked rat IgG2a bound to rat Fc epsilon RI transfected into CHO cells. Monomeric rat IgG2a, cross-linked rat IgG1, IgG2b, IgG2c and rabbit IgG did not bind to Fc epsilon RI. Stimulation of RBL-2H3 cells with aggregated IgG2a induced phosphorylation of tyrosines in the beta and gamma subunits of the Fc epsilon RI. Thus, although RBL-2H3 and rat peritoneal mast cel ls have Fc gamma R, the IgG-mediated stimulation of these cells for hi stamine release was by the Fc epsilon RI. Altogether, these data demon strate that the rat Fc epsilon RI is a functional receptor with low af finity for rat IgG2a.