1. Center for Molecular Medicine, Department of Medicine, Karolinska University Hospital, Karolinska Institutet, SE-17176 Stockholm, Sweden.
2. Department of Immunobiology, Yale University School of Medicine, New Haven, CT 06520, USA.
3. Department of Medical Biosciences/Physiological Chemistry, Umeå University, SE-90187 Umeå, Sweden.
4. Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06520, USA.