1. Department of Immunology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105.
2. Hartwell Center, St. Jude Children's Research Hospital, Memphis, Tennessee 38105.
3. Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, Tennessee 38105.
4. Department of Pediatrics, University of Tennessee, Memphis, Tennessee 38103.
5. Department of Pathology, University of Tennessee, Memphis, Tennessee 38103.
6. Department of Microbiology and Immunology, University of Melbourne, Melbourne, Vic 3010, Australia.