1. Department of Microbiology and Immunology, University of Iowa, Iowa City, IA 52242, USA
2. Graduate Program in Immunology, University of Iowa, Iowa City, IA 52242, USA
3. Department of Virology, Immunology, and Microbiology, National Emerging Infectious Diseases Laboratories, Boston University, Boston, MA 02118, USA
4. Department of Pathology and Laboratory Medicine, University of Wisconsin School of Medicine and Public Health, Madison, WI 53726, USA