Contents

10 April 1998
Vol 280, Issue 5361

About The Cover

An immune system given free rein is lethal. The road-blocks built into the system or introduced by pathogens are the topic of several Articles starting on 237 and the Editorial on 179a. Mutations of the immune system reveal developmental checkpoints and define mechanisms to turn lymphocytes off, such as the use of death receptors (red). Viruses (yellow) excel in putting up roadblocks to avoid detection, for example, by inhibiting major histocompatibility molecules (green) from moving to the cell surface. [Illustration: Katharine Sutliff]