TNFRSF17 and systemic lupus erythematosus: Additionally, the surface expression of BCMA on plasmablasts in SLE negatively correlated with serum BAFF levels (r = −0.41, p = 0.002), whereas BCMA expression on B cells significantly correlated with serum BAFF concentrations (r = 0.49, p = 0.013) (Figure 2E).