1. From the Center of Molecular Immunology and Infectious Diseases, Departments of Veterinary and Biomedical Sciences (M.X., K.Y., N.X.) and Nutrition (C.K.M.), Pennsylvania State University, University Park; Department of Molecular and Cell Biology, University of California, Berkeley (N.G., D.H.R.); and Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA (G.K.S., G.S.). Current address for N.G. is Division of Cell and Molecular Biology, Imperial College, London,...