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 mucosal 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 affecting the cell's secretory response to Fc epsilon RI clustering and hence named mast cell functional antigen (MAFA), and (3) a glycolipid, GD1b present in the RBL-2H3 cell's plasma membrane. The cross-reactivity of these mAbs with human basophils (from both allergic and nonallergic children) was now examined by three different protocols: (1) by microscopy (light and dark field) of double stained basophils by toluidine blue and by fluorescein-labeled anti-mouse antibodies as secondary ligands binding to the mAbs; (2) by flow cytometry (using directly labeled mAbs), and (3) by monitoring the binding of the 125I-radiolabeled mAbs. In order to exclude the possibility of the (intact) mAbs binding to the Fc gamma receptors, also present on human basophils, Fab and (Fab')2 fragments derived from the above respective mAbs were employed 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 employed as tools for studying the human basophils function.