Likewise, numerous neurotrophic factors and cytokines are known to support the survival of neurons and axons, including nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, neurotrophin-4/5, glial cell line-derived neurotrophic factor, CNTF (Ransohoff et al., 2002; Sofroniew et al., 2001) , insulin-like growth factor-1 (Kaspar et al., 2003) , vascular endothelial growth factor (Lambrechts et al., 2003) , hepatocyte growth factor (Sun et al., 2002) , cardiotrophin-like cytokine/cytokine-like factor 1 (Forger et al., 2003; Ransohoff et al., 2002) , and other immune cell-derived factors (Yin et al., 2003) .