CD38 and systemic lupus erythematosus: Corresponding with data from the Act1-/- mouse, SLE patient serum 25(OH)D3 was negatively correlated with memory B cells (CD19+IgD-CD27+CD38-) (p < 0.01) (Figure 6A,C), while there was no correlation between serum 25(OH)D3 and levels of naïve B cells (CD19+IgD+) (p = 0.16) or plasmablasts (CD19+IgD-CD27+CD38+) (p = 0.091) (Figure 6B,D).