Pe anti fcεri

The monoclonal Fel d 1-specific IgE and IgG antibodies used in these experiments have been described previously (14) . They have been genetically engineered to be expressed as either human or mouse antibodies and were produced in CHO cells (Evitria AG, Zürich, Switzerland) and purified by affinity chromatography over a protein L or protein G Sepharose column (GE Healthcare) respectively. The monoclonal Fel d 1-specific IgE F127 was chosen for subsequent activation and binding assays in this study. For activation assays, the mast cells were stained with FITC anti-CD63 (BD Bioscience, NJ, USA) antibodies. Marker expressions were assessed with APC anti-c-kit (Biolegend, San Diego, CA, USA), PE anti-FcεRI (Biolegend) and IgE binding with APC anti-IgE (Miltenyi Biotec, Bergisch Gladbach, Germany). Mast cell binding of Fel d 1 was assessed by staining with the FITC-labelled monoclonal mouse anti-Fel d 1 IgG recognizing the non-overlapping epitope G078 (14) .