1. From the Department of Microbiology and Immunology, University of Melbourne, Parkville, Victoria, Australia 3052; the Alfred Hospital, Prahran, Victoria, Australia 3181; the Department of Plastic Surgery, St. Vincent's Hospital, Melbourne, Victoria, Australia 3065; and the AIDS Pathogenesis Research Unit, Macfarlane Burnet Centre for Medical Research, Fairfield, Victoria, Australia 3078