Possible interactions between the Fcε receptor and a novel mast cell function-associated antigen

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Abstract
We have recently described a monoclonal antibody, mAb G63, which identifies a novel membrane component of mast cells. This antigen is a glycoprotein with an apparent molecular mass of 28–40 kd, and is present on the surface of rat mucosal and serosal mast cells. Its density on cells of the mucosal mast cell line RBL-2H3 is 1 − 2 × 104 copies per cell. Crosslinking of this membrane protein by the intact mAb G63 results in a pronounced inhibition of the FcεsRl-medlated secretion of RBL-2H3 cells. Here we show that crosslinking this novel membrane component inhibits biochemical processes initiated by FcεRl aggregation, such as the hydrolysis of phosphatidylinositides, the influx of Ca2+ ions, and the synthesis and release of de novo formed inflammatory mediators. Furthermore, by fluorescence microscopy, we show that crosslinking of FcεsRl-IgE complexes by multlvalent antigen results in redistribution of the membrane component recognized by G63, leading to its co-localization with the aggregated FcεsRl. This localization is inhibited by NaN3, but not by colchicine or cytochalasin D. FcεRl crosslinking also promotes internallzation of this novel membrane component. Taken together these data suggest that the mast cell membrane component recognized by mAb G63 is involved in the FcεRl-medlated stimulation of these cells, and thus can be considered a mast cell function-associated antigen (MAFA).

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