Among SSc patients a significant positive linear correlation was found between serum IgG levels and percentage of naive B cells (r = 0.472; p < 0.001) (Figure 3 panel A) and a significant negative linear correlation was observed between serum IgG levels and percentage of IgM-memory (r = −0.327; p < 0.05), switched-memory (r = −0.478; p < 0.001), double-negative (r = −0.310; p < 0.05), and CD21low B cells (r = −0.389; p < 0.01) (Figure 3 panel B). This evidence concerns the gene CD40LG and systemic sclerosis.