Further Characterization of FcγRII and FcγRIII Expression by Cultured Human Mast Cells

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Abstract
Background: We have reported that resting human mast cells exhibit minimal expression for FcγRI, and that interferon-γ will upregulate this expression. The expression of FcγRII and FcγRIII by human mast cells remains to be fully examined. Methods: To investigate FcγRII and FcγRIII expression, we determined mRNA and protein expression of FcγRII and FcγRIII in human peripheral blood CD34+ derived cultured mast cells by RT-PCR and flow cytometry. The expression of FcγRII and FcγRIII in intact and permeabilized mast cells was also compared. We measured histamine release to monitor mast cell degranulation following cross-linking of FcγRII. Results: We found by RT-PCR that resting human mast cells exhibit mRNA for FcγRIIA, FcγRIIb1, FcγRIIb2 and FcγRIII but not FcγRIIC. FACS analysis of Fcγ receptors in intact versus permeabilized mast cells showed expression of FcγRII to be 42.2 ± 3.9% and this was unchanged by permeabilization. FcγRIII protein expression was minimal and this was also unchanged by permeabilization. Aggregation of FcγRII on human mast cells led to no significant degranulation as evidenced by histamine release. Conclusions: In addition to FcγRI expression, human mast cells express FcγRIIA, FcγRIIb1, FcγRIIb2 and FcγRIII mRNA, and significant surface expression of FcγRII. Aggregation of FcγRII on cultured human mast cells in this model was not followed by histamine release.