1. New York Veteran Affairs Medical Center and Department of Pathology, New York University School of Medicine, New York, New York
2. Department of Immunology, Chelsea and Westminster Hospital, London SW 10 9NH, UK
3. Henry M. Jackson Foundation and Division of Retrovirology, Walter Reed Army Institute of Research, Rockville, Maryland 20850
4. Laboratory of Cellular Physiology and Immunology, Rockefeller University, New York, New York 10021