1. Division of Gastroenterology and Institute of Infections and Immunity; University of Nottingham; Nottingham NG7 2UH United Kingdom
2. Division of Infectious Diseases; Vanderbilt University, and Veterans Affairs Medical Center; Nashville TN 37232-2605
3. Department of Biomedical Science and Human Oncology, Section of General Pathology; University of Bari; 70124 Bari Italy
4. IRIS; Chiron S.p.A; 53100 Siena Italy