mAb BGD6, a mast cell lineage marker, binds to a 110kDa protein unrelated to FcεRI

Mast cells (MC) are multifunctional immune cells implicated in allergy and inflammation. They originate from committed precursors in the bone marrow and migrate as progenitor cells through the blood stream reaching peripheral tissues and maturing under the influence of microenvironment. The MC specific monoclonal antibody, mAb BGD6, binds to a 110 kDa protein on the surface of rodent MCs. mAb BGD6 recognizes MCs in all maturation stages, including committed MC precursors that do not express FcεRI on their surface. Our aim was to evaluate the physiological effects of mAb BGD6 binding on mast cells. Various concentrations of mAb BGD6 failed to degranulate RBL‐2H3 cells in both β‐hexosaminidase and histamine release assays. Also, the antibody's binding to the cell surface did not cause the release of the lipid mediator LTB4. The binding of mAbBGD6 to mast cell precursors as well as its lack of effect on the release of preformed and lipid mediators are consistent with the hypothesis that the 110kDa protein is not associated with FcεRI. We further investigated the involvement of mAb BGD6 surface binding on the activation of the transcription factors NFAT and NFkB. Using reporter cell lines for the activation of these factors, mAb BGD6 displayed no effect on NFAT, but resulted in some activation of NFkB suggesting that mAb BGD6 is activating a pathway other than FcεRI. This research is supported by FAPESP, Sao Paulo, Brazil.