An IgE-dependent secretory response of mast cells can be induced by a glycosphingolipid-specific monoclonal antibody

The signal transduction pathway of the type 1 Fc epsilon receptor (Fc epsil on RI) has been proposed to be spatially constrained to plasma membrane mic rodomains enriched in glycosphingolipids and cholesterol. These domains are proposed to serve as platforms that enhance the efficiency of the antigen- receptor stimulus-response coupling process. Here we describe a monoclonal antibody (mAb) designated 2B5, raised by immunizing mice with rat mucosal-t ype mast cell (line RBL-2H3) membranes, which binds to glycosphingolipids a nd causes a dose-dependent secretory response of these cells. This secretor y response to mAb 2B5 requires binding of IgE to the Fc epsilon RI on these cells, although direct interactions between IgE and mAb 2B5 are excluded. The bound IgE- or Fc epsilon RI-specific mAb did not affect binding of mAb 2B5 or its Fab fragments to the RBL-2H3 cells and only a limited interferen ce with the binding of IgE to the Fc epsilon RI by mAb 2B5 was observed. Bi nding of mAb 2B5 to the RBL-2H3 cells induced a distribution of fluorescent ly labeled IgE similar to that produced by antigen-induced aggregation of t he IgE-Fc epsilon RI. Thus we suggest that mAb 2B5 binds to cell surface gl ycosphingolipids that are probably associated with the Fc epsilon RI-IgE co mplexes and causes their aggregation, thereby initiating the cascade leadin g to the cell's secretory response.