Apoptosis, or programmed cell death, is of central importance for the regulation of the immune system. Articles in this special issue on cell death and immunity look at recent developments in this field. The term apoptosis was first used in the early 1970s to describe a form of cell death that is distinct from necrosis, the term being derived from the ancient Greek for falling of leaves — a concept that has inspired our cover this month.

Cytotoxic T lymphocytes and natural killer cells use common pathways to kill virus-infected or transformed cells. Judy Lieberman describes recent insights into the mechanisms of granule-mediated cytotoxicity, focusing on how granzymes activate apoptosis through caspase-independent pathways. But some viruses, such as HIV-1, have evolved ways to manipulate the cellular apoptotic machinery to their advantage, as discussed by Marie-Lise Gougeon.

Cell death is also essential during development. In the thymus, the processes of negative selection ensure that potentially self-reactive T cells are deleted. Our current understanding of the mechanisms that control these cell-death pathways in the thymus is outlined by Ed Palmer. Naohiro Inohara and Gabriel Nuñez focus on NOD proteins, a growing family of cytosolic proteins that are involved in immune responses and apoptosis.

This is our first joint project with Nature Immunology, which has a special issue on the same theme this month. Together, we have produced a web focus on cell death and immunity (http://www.nature.com/focus/celldeathimm), which is freely accessible until the end of June. This contains reviews from both journals, as well as original research papers, reviews and highlights from the Nature Publishing Group.