Apoptosis promoters spur cell division

Two cell-killing proteins also have a nurturing side, say Russell Jones, Craig Thompson (University of Pennsylvania, Philadelphia, PA), and colleagues. Although the proteins prod lymphocytes to commit suicide, they also prompt the cells to proliferate—and might do the same for a variety of cell types.

The two proteins, Bax and Bak, are part of the apoptotic machinery in T lymphocytes. Weeding out excess T cells turns down the immune response after a pathogen has been defeated. Mice that lack Bax and Bak in blood cells often fall victim to infections, suggesting that the two proteins are also involved in lymphocyte activation.

The researchers found that T cells missing Bak and Bax divided slowly after stimulation. Injecting bacteria into mice lacking both proteins in their lymphocytes didn't...