Is IL-6 both a cytokine and a neurotrophic factor?

The article by Hirota et al. (pp. 2627-2634) provides interesting evidence for the action of Interleukin-6 (IL-6) in the nervous system, but is it appropriate to consider IL-6 a neurotrophic factor; and, if so, what does this mean? The last decade has seen the discovery of a large number of neurotrophic and neural differentiation factors in both the peripheral and central nervous system. Examples of peptides with interesting activities in the nervous system include BDNF, NT-3, CNTF, GDNF, bFGF, aFGF, IL-3, IL-2, LIF, and others. The molecular characterization of growth factors has led to the realization that these peptides can play different roles in the nervous system and that they can also play important roles in many other