In yeterday's online of edition of Nature Neuroscience, researchers at Children's Hospital in Boston reported the discovery of a new growth factor that stimulated the growth of nerve fibers in the brain and spinal cord. This new factor, oncomodulin, induced in vitro a 5-7 fold increase in regeneration of axons from retinal ganglion cells. This protein is secreted by macrophages as an extremely acidic calcium-binding protein. Oncomodulin is found in both fetal placenta and neoplastic tissues. In their previous studies, the researchers fortuitously discovered that injury to the optic nerve activated axon growth. The activation process was initiated by macrophage infiltration to the tissue injury site as a result of inflammation. The nerve fibers respond to oncomodulin when intracellular levels of cyclic-AMP are increased. (It should be noted that these findings support the concept that in wound and tissue repair the inflammatory response results in debridement of the damaged tissues by phagocytic cells such as macrophages. Another interpretation of the data may be that infiltration of phagocytic cells leads to activation of resident undifferentiated stem cells to regenerate axons.)