Functional IL-4 receptors on mouse astrocytes: IL-4 inhibits astrocyte activation and induces NGF secretion.

IL-4 is a Th2-derived cytokine which plays an important role in the function of various immunocompetent cells as well as in the pathophysiology of various CNS disorders. In this study we characterized the expression of IL-4R in cultured astrocytes and explored the effects of IL-4 on the function of these cells. We found that astrocytes express the mRNA of both the membrane-bound and the soluble forms of the IL-4R, whereas they do not secrete IL-4. IL-4 inhibited both NO production and iNOS expression induced by LPS stimulation and decreased the secretion of TNF-alpha and the expression of ICAM-1. In contrast, IL-4 induced the secretion of NGF by astrocytes and synergized with LPS and TNF-alpha in this effect. These results suggest an important role for IL-4 as an immunosuppressive and a neurotrophic factor in the CNS.