1. Department of Immunohaematology, University Hospital, Leiden, Netherlands.
2. Department of Chemistry, University of Virginia, Charlottesville, VA 22903, USA.
3. Department of Microbiology and Beirne Carter Center for Immunology Research, University of Virginia, Charlottesville, VA 22908, USA.
4. Departments of Chemistry and Pathology, University of Virginia, Charlottesville, VA 22903, USA.