Immunological studies on patients with optic neuritis without evidence of multiple sclerosis.

We studied 6 patients with idiopathic optic neuritis (ON) after a mean follow-up period of 12 years. No evidence of multiple sclerosis (MS) was found on clinical grounds, nor by magnetic resonance imaging (MRI) or evoked responses. Levels of spontaneous proliferation, serum gamma-interferon (IFN-gamma) and lymphocyte MHC locus II antigen were similar in ON and in 6 patients with progressive MS, but different in healthy controls. This suggests that similar immunological conditions in vivo prevail after an idiopathic ON and in MS. A normal PHA-induced interleukin-2 receptor expression and lymphocyte proliferation but a low IFN-gamma secretion and MHC locus II antigen expression were observed. This suggests that an ON and MS defect is expressed after an interleukin-2 receptor ligand but before IFN-gamma secretion. Our findings also suggest that immunological factors do not explain the neuropathological confinement of the lesions in ON but the protective influence may rather be exerted by some as yet undefined genetic influence or may be explained by the different etiology of ON and MS.