Repairing for death

The targets of cytotoxic T lymphocytes (CTLs) determine their own mode of death, say Dennis Keefe, Judy Lieberman, and colleagues (Harvard Medical School, Boston, MA). The dying cells patch themselves up so that rapid and messy necrosis is avoided in favor of a more lengthy and controlled apoptosis.The CTLs deliver their insult in the form of perforin, a pore-forming protein that helps get proteases called granzymes into the target cell. The Boston group showed that perforin addition to a target cell induced a Ca²⁺ transient and a massive plasma membrane repair response. Similar Ca²⁺-induced responses, in which lysosomal and other membranes are recruited to patch up plasma membrane holes, are known to be induced by mechanical damage to cell membranes.

Blocking the rise in Ca²⁺ and thus the repair response resulted...