1. Department of Medicine, Weill Medical College of Cornell University, New York, New York 10021
2. Department of Immunology, DNAX Research Institute of Molecular and Cellular Biology, Palo Alto, California 94304
3. Laboratory of Cellular Physiology and Immunology, The Rockefeller University, New York, New York 10021
4. Department of Pathology, New York University School of Medicine, New York, New York 10016