1. Department of Immunology and Microbial Science, The Scripps Research Institute, La Jolla, California 92037
2. DuPont Central R&D, Experimental Station, E328/203 L, Wilmington, Delaware 19880-0328
3. Department of Microbiology & Immunology, Loyola University Chicago, Maywood, Illinois 60153
4. Department of Biological Chemistry, David Geffen School of Medicine and California NANOSystems Institute, University of California, Los Angeles, California 90095