Mouse immunization and sampling
BALB/c mice (Envigo, Huntingdon, UK) were used at 8 to 12 weeks and kept at the central animal facility (Murtenstrasse 31, Bern, Switzerland). All animals were treated for experimentation according to protocols approved by the Swiss Federal Veterinary Office. Prof. J. Ravetch kindly provided CD23-/- mice. FcγRIIb -/- mice (Jackson Laboratory, Bar Harbor, Maine, MA, USA) were purchased at 6 weeks and bred in our facility. All animals were acclimatized to the facility for at least one week.
IgE-Fel d 1 complexes were formed for immunizations by incubating 25µg IgE and 5µg Fel d 1 for 1h at 37°C dissolved in 100µl PBS before intravenous (i.v.) injection into mice.
To analyze IgE clearance, mice were injected with or without 25µg anti-IgE IgG or anti-IgE IgG(PNG) 1h before receiving 25µg IgE intravenously. Blood from tail veins was collected using Microtainer® serum tubes (BD Biosciences, Franklin Lakes, NJ, USA) or in PBS containing 10mM EDTA (Sigma-Aldrich, St Louis, Mo, USA). Blood was collected from naïve mice, 30 minutes, 2 hours, and 24 hours after IgE injection.