1. Institute for Genetics, University of Cologne, Germany.
2. Bristol-Myers Squibb, Pharmaceutical Research Institute, Seattle, WA 98121, USA.
3. Institute of Experimental Immunology, Department of Pathology, University of Zurich, CH-8091 Zurich, Switzerland.
4. Department of Microbiology and Immunology, University of California, San Francisco, CA 94143, USA.