The CD8+ T cell model of action by GA. MHC class I restricted CD8⁺ T cell responses to GA, which are significantly lower at baseline in MS patients than in healthy controls, increase significantly following treatment, as seen in the greater number of IFN-γ–positive, GA responsive CD8⁺ T cells. GA treatment is proposed to restore CD8⁺ suppressor function, which is dependent upon IFN-γ secretion. The mechanism for CD8⁺ suppression of the immune response is unknown. Shown in the figure is a CD8⁺ T cell migrating to the CNS, regulating a CD4⁺ autoreactive T cell.