1. Center for Blood Research, 800 Huntington Avenue, Boston, Massachusetts 02115, Departments of Biochemistry and Urology, University of Washington, Seattle, Washington 98195, Department of Pulmonary and Critical Care Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115, Department of Dermatology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, and Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02115