1. Immunobiology Program, Department of Medicine, Given Medical Building, University of Vermont, Burlington, VT 05405
2. Howard Hughes Medical Institute and Program in Molecular Medicine, Department of Biochemistry and Molecular Biology, University of Massachusetts Medical School, Worcester, MA 01605
3. Department of Molecular Pathology, Institute of Pathology, University of Würzburg, D-97080 Würzburg, Germany
4. Department of Biology, University of North Carolina at Charlotte, Charlotte, NC 28223