RBL-2H3 cells (Cell Bank, RIKEN BioResource Center, Tsukuba, Japan) were cultured in Dulbecco’s modified Eagle’s medium supplemented with 10% heat-inactivated fetal bovine serum, 100 U/mL penicillin, and 100 g/mL streptomycin at 37 °C in a humidified atmosphere containing 5% CO2.