1. T. G. Diacovo, Center for Blood Research and Department of Cardiology, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA, and Division of Newborn Medicine, Department of Pediatrics, Tufts University School of Medicine, Boston, MA 02111, USA.
2. K. D. Puri, T. A. Springer, U. H. von Andrian, Center for Blood Research and Department of Pathology, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA.
3. R. A. Warnock, Department of Pathology, Stanford University, Stanford, CA 94305, USA.