Monocyte inducible nitric oxide synthase in multiple sclerosis: regulatory role of nitric oxide

Immunophenotypic analysis of peripheral blood leukocytes from patients with multiple sclerosis (MS) showed a profile reflecting a state of activation and differentiation of monocytes. A subset of CD16+ monocytes with high HLA-DR expression was more prominent in patients with MS than in healthy subjects. The presence of the inducible form of nitric oxide synthase (iNOS) in these differentiated and activated monocytes freshly obtained from patients with MS was demonstrated by immunocytochemistry and flow cytometry analysis with two different antibodies. Incubation of lymphomononuclear cells from healthy volunteers in the presence of an immunomodulating peptide (NVLGAPKKLNESQAV) led to stimulation and maturation of monocytes manifested by changes in phenotype and an increase in both iNOS mRNA and protein, as well as HLA-DR expression. In this case also iNOS was expressed mainly on subsets of CD16+ monocytes with high HLA-DR expression. NO produced by human monocytes seems to have a function in the upregulation of membrane HLA-DR. These results are suggestive of a role for monocytic iNOS in the autoimmune response underlying the pathogenesis of multiple sclerosis.