Is war necessary (for transplant success)?

If immune cells are an army, then a graft transplant is a foreign invasion. New work by Yu et al. on page 1851 shows that antigen-presenting cells (APCs) from the graft are rapidly killed by the host's first line of defense: natural killer (NK) cells. But far from hindering the chance of graft survival, this battle actually improves it.

NK cells are known to improve the chance of graft survival, but how they do this was unknown. Li's team wanted to know what happens to graft APCs when NK cells are absent.

Using mice that lacked a full-blown rejection response (because they lacked lymphocytes), the team were able to follow the fate of donor APCs for longer than would normally be possible. They found that in the absence of NK cells, donor...