1. Department of Microbiology, Immunology and Molecular Genetics, University of California Los Angeles, 609 Charles E. Young Drive East, Los Angeles, CA 90095, USA.
2. Medical Scientist Training Program, David Geffen School of Medicine at the University of California Los Angeles, 23-385 Center for the Health Sciences, Box 957041/MC:704117, Los Angeles, CA 90095, USA.