1. J. M. M. den Haan, J. Pool, E. Blokland, C. Reinhardus, R. Offringa, E. Goulmy, Department of Immunohematology and Bloodbank, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, The Netherlands.
2. L. M. Meadows, T. L. Bishop, J. Shabanowitz, Department of Chemistry, University of Virginia, Charlottesville, VA 22901, USA.
3. W. Wang and V. H. Engelhard, Department of Microbiology and the Beirne Carter Center for Immunology Research, University of Virginia, Charlottesville, VA 22908, USA.
4. D. F. Hunt, Departments of Chemistry and Pathology, University of Virginia, Charlottesville, VA 22901, USA.