CNS-specific CD4⁺ and CD8⁺ T-cell responses in a patient with MS. CFSE-based proliferation assays were performed on PBMC specimens from 8 healthy individuals and 43 untreated patients with MS (RRMS, n = 17; PPMS, n = 20; SPMS, n = 6). (A) Selected responses from a patient with MS in the presence (or absence) of indicated antigenic peptide pools. These data represent gated CD3⁺ T cells that are further gated for CD4⁺/CD8^- or CD8⁺/CD4^- T cells. CFSE staining is shown on the x-axis and CD8 staining on the y-axis. The CD8^- populations in the dot plots represent gated CD4⁺ T cells. The gray populations to the right represent nondividing cells. The numbers next to the darker populations represent the proliferating fraction of CD4⁺ T cells (black) and CD8⁺ T cells (dark gray) (ie, the proportion of gated CD4⁺ T cells or CD8⁺ T cells that were proliferating on day of analysis). Values for background proliferation are calculated from the “No Antigen” tubes. Δ proliferating fraction (ΔPF) is the difference between specific proliferation and the background, whereas the stimulation index (SI) is the ratio of specific proliferation to the background. A response with a ΔPF of at least 1.00% and an SI of at least 2.0 was considered positive. (B) CD4⁺ (left) and CD8⁺ (right) T-cell responses of the same patient to all the indicated antigens, plotted as ΔPF (background subtracted). The positive responses are indicated with a “+” sign.