Figure 2. JCV index.

(A) Fifty samples of natalizumab-treated patients with multiple sclerosis were assessed twice for their anti-JCV antibody index (JCV index) with an R² of 0.89. Eight of these 50 samples (16%) showed 2 different risk associations with the thresholds JCV−/+, JCV index 0.4, 0.9, 1.2, and 1.5 in the 2 assessments. (B) JCV index value distributions of a longitudinal cohort of 525 patients at the start and end of the period of observation of 14.8 months. (C) Serial assessment of JCV index values of 525 patients alongside their natalizumab therapy (2–7 JCV serology assessments). Red lines indicate the thresholds 0.4, 0.9, and 1.5. (D) Serial assessment of JCV index values. Only patients whose index values changed by more than 30% over time and whose PML risk group changed are shown (0–0.4 [green], 0.4–0.9 [yellow], 0.9–1.5 [orange], >1.5 [red]). JCV = John Cunningham virus.