1 Laboratory of Immunoregulation, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland. Electronic address: roccojm@nih.gov.
2 Division of Infectious Diseases, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania.
3 Laboratory of Immunoregulation, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland.