Inflammatory cells and their products contribute to neuronal survival and axonal regeneration after injury. Following sciatic nerve transection in rats, macrophages accumulate in the corresponding dorsal root ganglion, potentially supplying neurotrophic support to nerve cell bodies, and enhancing axonal regeneration. Growth factors characterized for their functions in the haematopoietic and immune systems also act on neurons and vice versa, by sharing common subunits among receptors for cytokines and neurotrophic factors.