CD40 and systemic lupus erythematosus: Intriguingly, lupus MDSCs significantly promoted R848-induced expression of CD86 and CD40 on BMDMs and the secretion of IL-12 and TNF-α by BMDMs, whereas neutralizing S100A9 markedly reversed the promoting effect of lupus MDSCs on R848-induced expression of CD86 and CD40 on BMDMs (Fig. 4F, G) and the secretion of IL-12 and TNF-α by BMDMs (Fig. 4H, I).