1. From the Research Service, Albuquerque Veterans Administration Medical Center, Albuquerque, New Mexico 87108
2. Department of Molecular Genetics and Microbiology, University of New Mexico, Albuquerque, New Mexico 87131
3. Department of Pathology, University of New Mexico, Albuquerque, New Mexico 87131
4. Department of Laboratory Medicine, University of California, San Francisco, San Francisco, California 94143
5. Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213