1. Department of Veterinary Internal MedicineGraduate School of Agricultural and Life SciencesUniversity of Tokyo1‐1‐1 Yayoi Bunkyo‐kuTokyo113‐8657Japan
2. Department of ImmunologyNational Institute of Infectious Diseases1‐23‐1 Toyama, Sinjuku‐kuTokyo162‐8640Japan