CD27 and systemic sclerosis: We found that only topo I-APC+ topo I-PE+ CD27+ CD19+ cells from anti-topo I antibody-positive SSc patients produced IgG anti-topo I antibodies with an average titer of +6 SD or higher, but these B cells from healthy individuals or anti-CENP antibody-positive SSc patients did not produce IgG anti-topo I antibodies (Figure 1B).