CD27 and systemic sclerosis: To this end, topo I-reactive CD27+ B cells (200 cells from 58 anti-topo I antibody-positive SSc patients) were divided into the low-affinity group (80 cells) and high-affinity group (120 cells), according to IgG anti-topo I antibody titers (Figure 2A): titers of IgG anti-topo I antibodies in the low-affinity group were 2–4 SD above the background, whereas titers of the high-affinity group were 6–8 SD above it.