1. Faculty of Medicine, University of Southampton, Southampton, United Kingdom.
2. VA San Diego Healthcare System and Veterans Medical Research Foundation, San Diego, California, USA.
3. Department of Microbiology, Immunology and Tropical Medicine, The George Washington University, Washington, District of Columbia, USA.
4. Department of Pathology and University of California San Diego, La Jolla, California, USA.
5. Department of Medicine, University of California San Diego, La Jolla, California, USA.