The combination of low IgE and decreased mast cell numbers rendered the OVA IgG-treated animals completely resistant to anaphylaxis, with no signs of hypothermia, a cardinal physiologic feature of anaphylaxis in mice, or elevated levels of plasma mast cell protease-1 (MMCP-1), a granule protease and marker of mast cell activation analogous to tryptase in humans. The gene discussed is IGHE; the disease is anaphylaxis.