1. Department of Microbiology and Immunology, Keio University School of Medicine, Shinjuku-ku, Tokyo, Japan
2. Next Generation Science Institute, Morinaga Milk Industry Co., Ltd., Zama, Kanagawa, Japan
3. Laboratory of Animal Food Function, Graduate School of Agricultural Science, Tohoku University, Aobaku, Sendai, Japan
4. Livestock Immunology Unit, International Education and Research Center for Food Agricultural Immunology, Graduate School of Agricultural Science, Tohoku University, Aobaku, Sendai, Japan
5. Electron Microscope Laboratory, Keio University School of Medicine, Shinjuku-ku, Tokyo, Japan
6. Department of Animal Science, School of Veterinary Medicine, Kitasato University, Aomori, Japan