1. Department of Pathology, University of Birmingham, Birmingham B15 2TT, U.K.
2. Second Department of Internal Medicine, Tohoku University School of Medicine, Aoba‐ku, Sendai 980, Japan
3. Department of Pathology, University of Sheffield Medical School, P.O. Box 596, Beech Hill Road, Sheffield S10 2UL, U.K.
4. Department of Histopathology, King's College School of Medicine and Dentistry, London SE5 8RX, U.K.