1. C. A. Mallick-Wood, L. I. Richie, A. C. Hayday, Department of Molecular, Cell, and Developmental Biology and Section of Immunobiology, Yale University, New Haven, CT 06520, USA.
2. J. M. Lewis and R. E. Tigelaar, Department of Dermatology and Section of Immunobiology, Yale University, New Haven, CT 06511, USA.
3. M. J. Owen, Imperial Cancer Research Fund, Lincoln's Inn Fields, London WC2A 3PX, UK.