1. MRC Virology Unit, Institute of Virology, University of Glasgow, Church Street, Glasgow G11 5JR, UK
2. The Institute of Infection, Immunity and Inflammation, School of Molecular Medical Sciences, The University of Nottingham, Queen's Medical Centre, Nottingham NG7 2UH, UK
3. Department of Pathology, Stanford University School of Medicine, Stanford, CA 94305, USA