Shared resources between the neural and immune systems: semaphorins join the ranks.

The semaphorin family of molecules contains members known to deliver guidance cues to migrating axons during development. Semaphorins also have been identified on the surface of hematopoietic cells and, interestingly, in the genomes of certain lytic viruses. Recent studies indicate that semaphorins bind with high affinity to at least two different receptor families and are biologically active on immune cells as well as neuronal cells.