Expression of the inducible isoform of nitric oxide synthase in the central nervous system of mice correlates with the severity of actively induced experimental allergic encephalomyelitis

A cytokine-mediated excessive increase in nitric oxide (NO) by macrophages or glial cells via an inducible isoform of NO synthase (iNOS) has been proposed to play an important role in demyelinating diseases. To further investigate the role of iNOS in demyelination, experimental allergic encephalomyelitis (EAE), a known animal model of multiple sclerosis (MS) in mice, was chosen in this study. A semiquantitative reverse transcriptase-polymerase chain reaction (RT/PCR) analysis revealed an increase in the mRNA levels of iNOS and cytokines known to induce iNOS or inflammatory cytokines (interleukin (IL)-1α, IL-1β, IL-2, IL-6, interferon (IFN)-γ, tumor necrosis factor (TNF)-α and TNF-β) in the spinal cord corresponding to the severity of the disease without significant change in the mRNA levels of immunoregulatory cytokines (IL-4, IL-10 and transforming growth factor (TGF)-β) during the course of EAE. An immunohistochemical examination of the spinal cord using an iNOS-specific antibody showed iNOS-positive cells to be mainly inflammatory cells with a higher frequency of iNOS-positive cells at the peak of EAE than in the early phase. These iNOS-positive cells at the peak appeared to be composed of infiltrating macrophages and most of them were located in the necrotic area. These results suggested that cytokine-induced excessive NO via iNOS by macrophages caused tissue damage in the central nervous system in EAE.