1. Department of Microbiology-Immunology; Northwestern University Medical School; 320 E. Superior St., Searle 6-573 Chicago IL 60611
2. Department of Microbiology and Immunology, Chandler Medical Center; University of Kentucky; 800 Rose St. Lexington KY 40536
3. Abteilung für Transfusionsmedizin; Universitätsklinikum Tübingen; Otfried-Müller-Str. 4/1 D-72076 Tübingen Germany