1. Department of Cell Biology, University Medical Center, Institute of Biomembranes and Center for Biomedical Genetics, 3584 CX Utrecht, Netherlands
2. Department of Immunohaematology and Blood Transfusion, Leiden University Medical Center, 2300 RC Leiden, Netherlands
3. Department of Biotechnology and Bioscience, University of Milano-Bicocca, 20126 Milan, Italy
4. Howard Hughes Medical Institute, University of Washington, School of Medicine, Seattle, WA 98195