1. Department of Internal Medicine and Clinical Investigation, Institut Jules Bordet, Brussels, Belgium, and the Department of Blood Transfusion of the University Hospitals, Brussels, Belgium.
2. Hematology Research Laboratory, Massachusetts General Hospital, Boston, Mass.
3. Service de Médecine, Hôpital Universitaire Brugmann, Brussels, Belgium.
4. Service de Médecine et d'Investigation Clinique, Institut Jules Bordet, Brussels, Belgium.
5. Service dc Médecinc et d'Investigation Clinique, Institut Jules Bordet, Brussels, Belgium.