ANTIBODIES SPECIFIC TO MEMBRANE-COMPONENTS OF RAT MAST-CELLS ARE CROSS-REACTING WITH HUMAN BASOPHILS

Murine monoclonal antibodies (mAbs) have previously been raised by us with specificity to the following plasma membrane components of rat mu cosal mast cells (RBL-2H3 subline): (1) the alpha-subunit of the type I Fc epsilon receptor, (Fc epsilon RI); (2) a newly described membrane glycoprotein, distinct from any of the Fc epsilon RI subunits, yet af fecting the cell's secretory response to Fc epsilon RI clustering and hence named mast cell functional antigen (MAFA), and (3) a glycolipid, GD(1b) present in the RBL-2H3 cell's plasma membrane. The cross-react ivity of these mAbs with human basophils (from both allergic and nonal lergic children) was now examined by three different protocols: (1) by microscopy (light and dark field) of double stained basophils by tolu idine blue and by fluorescein-labeled anti-mouse antibodies as seconda ry ligands binding to the mAbs; (2) by flow cytometry (using directly labeled mAbs), and (3) by monitoring the binding of the I-125-radiolab eled mAbs. In order to exclude the possibility of the (intact) mAbs bi nding to the Fc(gamma) receptors, also present on human basophils, Fab and (Fab')(2) fragments derived from the above respective mAbs were e mployed wherever necessary. The results show that the above described murine mAbs fragments do bind specifically to basophils obtained from allergic and nonallergic children. These antibodies may thus also be e mployed as tools for studying the human basophils function.