Theoretical Biology & Bioinformatics, Utrecht University, Utrecht, The Netherlands.|Department of Pathology, Harvard Medical School, Boston, Massachusetts, United States of America.|Lymphocyte Biology Section, National Insitutes of Health, Bethesda, Maryland, United States of America.|Department of Pathology, Harvard Medical School, Boston, Massachusetts, United States of America.|Institute for Anatomy, University of Lübeck, Lübeck, Germany.|Theoretical Biology & Bioinformatics, Utrecht University, Utrecht, The Netherlands.|Theoretical Biology & Bioinformatics, Utrecht University, Utrecht, The Netherlands, Division of Immunology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.