INDUCIBLE NITRIC-OXIDE SYNTHASE IN THEILERS MURINE ENCEPHALOMYELITIS VIRUS-INFECTION

We investigated the role of inducible nitric oxide synthase (iNOS) in Theiler's murine encephalomyelitis virus (TMEV) infection of susceptib le (SJL) and resistant (C57BL/6 [B6]) strains of mice. TMEV is an exce llent model of virus-induced demyelinating disease, such as multiple s clerosis (MS). Precious studies of others have suggested that NO may p lay a role in the pathogenesis of demyelinating disease. The presence and level of iNOS were determined in the brains and spinal cords of SJ L and B6 TMEV-infected mice by the following methods: (i) PCR amplific ation of iNOS transcripts, followed by Southern blotting with an iNOS- specific probe, and (ii) immunohistochemical staining with an anti-iNO S-specific affinity-purified rabbit antibody, iNOS-specific transcript s were determined in the brains and spinal cord of both SJL and B6 TME V-infected mice on days 0 (control), days 3, 6, and 10 (encephalitic s tage of disease), and days 39 to 42, 66, and 180 (demyelinating phase) postinfection (p.i.), iNOS-specific transcripts were found in the bra ins and spinal cords of both SJL and B6 TMEV-infected mice at 6, 10, a nd 39 (SJL) days p.i., but they were absent in mock-infected mice and in TMEV-infected SJL and B6 mice at 0, 3, 66, and 180 days p.i. Immuno histochemical staining confirmed the presence of iNOS protein in both TMEV-infected SJL and B6 mice at days 6 and 10 p.i., but not at days 0 , 3, 66, and 180 days p.i. Weak iNOS staining was also observed in TME V-infected SJL mice at 42 days p.i. iNOS-positive staining was found i n reactive astrocytes surrounding areas of necrotizing inflammation, p articularly in the midbrain. Weak iNOS staining was also observed in c ells of the monocyte/macrophage macrophage lineage in areas of parench ymal inflammation and necrosis (mesencephalon) and in leptomeningeal a nd white matter perivascular infiltrates of the spinal cord. Rod-shape d microglia-like cells and foamy macrophages (myelin-laden) were iNOS negative. These results suggest that NO does not play a direct role in the late phase of demyelinating disease in TMEV-infected mice.