Interleukin-6 (IL-6): a possible neuromodulator induced by neuronal activity.

IL-6 and its receptor(s) are found in the CNS in health and disease. Cellular sources are glial cells and neurons. Glial production of IL-6 has intensively been studied, but comparatively little is known about the induction of IL-6 in neurons. Emerging evidence suggests that IL-6 possesses neurotrophic properties. Recent data show that neuronal IL-6 expression is induced by excitatory amino acids or membrane depolarization. This implicates that IL-6 is produced not only under pathological conditions but may play a critical role as a physiological neuromodulator that is induced by neuronal activity and regulates brain functions. In the following article, the authors review the current data on IL-6 expression in neurons, with special reference to the induction of IL-6 by neuronal activity. They discuss its direct and indirect effects as a neuromodulator and speculate about the possible function of IL-6 as a physiological regulatory molecule and as a neuroprotective agent in brain pathology.