1. Department of Pathology, University of North Carolina, Chapel Hill, NC 27599-7525, USA.
2. Department of Pediatrics, University of North Carolina, Chapel Hill, NC 27599-8180, USA.
3. Department of Internal Medicine, Durham Veterans Affairs Medical Center, Durham, NC 27710, USA.
4. Department of Medicine, University of North Carolina, Chapel Hill, NC 27599-7035, USA.
5. Departments of Oral Biology and Medical Microbiology and Immunology, Ohio State Health Sciences Center, Columbus, OH 43210-1239, USA.
6. CRC Beatson Laboratories, Bearsden, Glasgow, G61 1BD, UK.