CD19 and systemic lupus erythematosus: Expression of p-STAT3 and STAT3 proteins was detected at higher levels in sorted CD19+CD5+CD1dhigh B cells from MRL/lpr mice than in sorted cells from B6 mice (Figure 4B), and this finding suggests that activation of STAT3 may contribute to the expansion of B10 cells in lupus-prone MRL/lpr mice.