1. Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut, USA
2. Department of Microbiology and Immunology, University of Illinois at Chicago College of Medicine, Chicago, Illinois, USA
3. Department of Molecular Biophysics and Biochemistry, W. M. Keck Foundation Biotechnology Resource Laboratory, Yale University School of Medicine, New Haven, Connecticut, USA
4. Howard Hughes Medical Institute, Chevy Chase, Maryland, USA