1. Laboratory of Immunoregulation, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892.
2. Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892.
3. Department of Pathology, George Washington University Medical Center, Washington, DC 20037.
4. Department of Pathology, Northwestern University Medical School, Chicago, IL 60611.
5. Armed Forces Institute of Pathology, Washington, DC 20306-6000.
6. Section of Neurovirology, Infectious Diseases Branch, National Institute of Neurological and Communicative Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.