A mouse Fcγ-Fcε protein that inhibits mast cells through activation of FcγRIIB, SH2 domain–containing inositol phosphatase 1, and SH2 domain–containing protein tyrosine phosphatases.

Background: A human Fcγ-Fcε fusion protein (GE2) designed to inhibit FcεRI signaling by coaggregating FcεRI with the inhibitory receptor FcγRIIB has been shown to inhibit mast cell activation and block cutaneous anaphylaxis. A critical issue remained as to whether the mechanism of GE2 inhibition is competition for IgE binding or inhibitory signaling through FcγRIIB. Objective: Our aim was to define the in vitro and in vivo mechanism of action of a mouse homolog of GE2 (mGE) and to assess the potential of human GE2 (hGE2) for therapeutic administration. Methods: The in vitro activity of mGE on mediator release and signaling pathways was characterized in IgE-sensitized bone marrow–derived mast cells (BMMCs). The in vivo activity of mGE was examined in mouse passive cutaneous and passive systemic anaphylaxis models, and the therapeutic activity of hGE2 was evaluated in Ascaris suum–sensitized cynomolgus monkeys. Results: mGE inhibited release of histamine and cytokines by BMMCs from wild-type mice but not by BMMCs from FcγRIIB-deficient mice. In mice mGE blocked IgE-dependent anaphylaxis mediated by mast cells with sustained efficacy. In BMMCs mGE decreased spleen tyrosine kinase and extracellular signal-regulated kinases 1/2 phosphorylation and induced FcγRIIB phosphorylation and the subsequent recruitment of SH2 domain–containing inositol polyphosphate 5′ phosphatase (SHIP) 1 and SH2 domain–containing protein tyrosine phosphatase (SHP) 1/2 phosphatases. When administered therapeutically, hGE2 protected sensitized monkeys from local anaphylaxis for 3 weeks. Conclusion: mGE-mediated inhibition of mast cell activation is associated with inhibitory signaling through FcγRIIB that results from activation of SHIP-1 and SHP-1/2 phosphatases. [Copyright &y& Elsevier]