Flow cytometry analysis revealed a significant higher proportion of circulating CD19+ CD138+ plasma cells in 23 SLE patients (0.22 (0.12, 0.33) %) compared to those in 23 healthy controls (0.08 (0.05, 0.12) %, p<0.0001) (Figure 3C), and percentages of CD19+ CD138+ cells was positively correlated with percentages of CXCR5+ PD1+/CD4+ cells in SLE patients (Pearson r = 0.45, p = 0.031) (Figure 3D). Here, SDC1 is linked to systemic lupus erythematosus.