Especially in active SLE patients (SLEDAI-2k ≥ 6 with a clinical SLEDAI-2k (excluding laboratory results) score ≥ 4), Mcl-1 expression was decreased after stimulation with CpG for 6 days, which supports previous studies showing that active SLE is associated with reduced cytokine production, proliferation and activation upon stimulation with a TLR9 agonist compared to healthy controls [23]. Here, TLR9 is linked to systemic lupus erythematosus.