1. Departments of Immunology and Molecular Biology, The Scripps Research Institute, La Jolla, California 920371;
2. Special Pathogens Branch, Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia 303332; and
3. Pathology Division, U.S. Army Medical Research Institute of Infectious Diseases, Fort Detrick, Maryland 217023