Further characterization of FcgammaRII and FcgammaRIII expression by cultured human mast cells

We have reported that resting human mast cells exhibit minimal expression for FcgammaRI, and that interferon-gamma will upregulate this expression. The expression of FcgammaRII and FcgammaRIII by human mast cells remains to be fully examined. To investigate FcgammaRII and FcgammaRIII expression, we determined mRNA and protein expression of FcgammaRII and FcgammaRIII in human peripheral blood CD34+ derived cultured mast cells by RT-PCR and flow cytometry. The expression of FcgammaRII and FcgammaRIII in intact and permeabilized mast cells was also compared. We measured histamine release to monitor mast cell degranulation following cross-linking of FcgammaRII. We found by RT-PCR that resting human mast cells exhibit mRNA for FcgammaRIIA, FcgammaRIIb1, FcgammaRIIb2 and FcgammaRIII but not FcgammaRIIC. FACS analysis of Fcgamma receptors in intact versus permeabilized mast cells showed expression of FcgammaRII to be 42.2 +/- 3.9% and this was unchanged by permeabilization. FcgammaRIII protein expression was minimal and this was also unchanged by permeabilization. Aggregation of FcgammaRII on human mast cells led to no significant degranulation as evidenced by histamine release. In addition to FcgammaRI expression, human mast cells express FcgammaRIIA, FcgammaRIIb1, FcgammaRIIb2 and FcgammaRIII mRNA, and significant surface expression of FcgammaRII. Aggregation of FcgammaRII on cultured human mast cells in this model was not followed by histamine release.