1. Department of Microbiology and Immunology, Stanford University School of Medicine,Stanford, CA 94305-5402,USA
2. Molecular and Cell Biology, University of Aberdeen, Institute of Medical Sciences,Foresterhill, Aberdeen AB25 2ZD,UK
3. Zeneca Pharmaceuticals, Alderley Park, Macclesfield SK10 4TG,UK
4. Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases,Hamilton, MT 59840,USA