Fc receptor beta subunit is required for full activation of mast cells through Fc receptor engagement

The high-affinity IgE receptor (Fc epsilon RI) and the low-affinity IgG rec eptor (Fc gamma RIII) on mast cells are the key molecules involved in trigg ering the allergic reaction. These receptors share the common beta subunit (FcR beta) which contains an immunoreceptor tyrosine-based activation motif and transduces the signals of these receptors' aggregation. In rodents, Fc R beta is essential for the cell surface expression of the Fc epsilon RI, I n humans, the FcR beta gene was reported to be one of the candidate genes c ausing atopic diseases. However, the role of FcR beta in vivo still remains ambiguous. To elucidate the functions of FcR beta, we developed the mice l acking FcR beta [FcR beta(-/-)]. The FcR beta(-/-) mice lacked the expressi on of the Fc epsilon RI on mast cells and IgE-mediated passive cutaneous an aphylaxis (PCA) was not induced in FcR beta(-/-) mice as was expected. In t hese mice, the expression of IgG receptors on mast cells was augmented but the IgG-mediated PCA reaction was attenuated. Although with bone marrow-der ived cultured mast cells from FcR beta(-/-), adhesion to fibronectin and Ca 2+ flux upon aggregation of IgG receptors were enhanced, mast cells co-cult ured with 3T3 fibroblasts exhibited impaired degranulation on receptor aggr egation. These observations indicate that FcR beta accelerates the degranul ation of mature mast cells via the IgG receptor in connective tissues.