Induction of nitric oxide synthase in cytokine‐stimulated human astrocytes by interleukin‐12 P40 monomer

Abstract

Excessive production of IL‐12 participates in the neuroinflammatory disease process of Multiple Sclerosis (MS). IL‐12 is composed of two different subunits – p40 and p35. However, it has been found that p40 but not that p35 is expressed in excessive amount in the CNS of MS patients. However, the biological significance of this overexpression of p40 in the CNS of patients with MS is not known. The present study underlines the importance of human IL‐12 (p70, the heterodimeric form) and p40 monomer in inducing the expression of iNOS in IFN‐g‐stimulated human astrocytes. IL‐12, p40 or IFN‐γ alone was poor inducer of NO production in human U373MG astrocytoma cells. However, the combination of either IL‐12 and IFN‐γ or p40 and IFN‐γ but not that of the IL‐12 and p40 markedly induced the production of NO. This induction of NO production was accompanied by an induction of iNOS protein and mRNA. Similar to U373MG astrocytoma cells, IL‐12 or p40 also induced the production of NO in human primary astrocytes. Although IFN‐γ alone was a weak inducer of NF‐κB activation, it efficiently induced the activation of CCAAT/enhancer‐binding protein (C/EBP)b and g‐activation site (GAS). On the other hand, p40 alone induced the activation of NF‐κB and C/EBPb but not that of GAS suggesting that p40 alone cannot induce the expression of iNOS probably due to its inability to induce the activation of GAS. This study delineates a novel role of IL‐12 p70 or IL‐12 p40 monomer in inducing the expression of iNOS in human astrocytes which may participate in the pathogenesis of neuroinflammatory diseases.Acknowledgements: This study was supported by NIH grants (NS39940 and AG19487).