1. Cardiovascular Research Institute, University of California, San Francisco, CA 94158–9001, USA.
2. Immunology Program, Stanford University, Stanford, CA 94305, USA.
3. Department of Microbiology and Immunology, University of California, San Francisco, CA 94158–9001, USA.
4. Department of Physiology and Department of Medicine, University of California, San Francisco, CA 94158–9001, USA.