QA increases heme-mediated inhibition of B-cell activation. (A-B) Fold change in plasma cell frequency in 7-day stimulated purified naïve HD B cells in the presence of 2.5 μM QA, AQ, CQ, or DHA without or with 5 μM heme relative to untreated but stimulated cultures (A), or different doses of QA plus 2.5 μM or 5 μM heme (B). (C) Levels of HO-1 expression (MFI) in proliferated B cells of 7-day stimulated B cells treated with different doses of QA without or with 5 μM heme. (D) Fold change in HO-1 expression in stimulated B cells in the presence of 2.5 μM QA, AQ, CQ, or DHA without or with 5 μM free heme relative to untreated but stimulated cultures. (E) Fold change in plasma cell frequency in stimulated purified naïve B cells from allo-positive and allo-negative patients in the presence of different doses of QA plus 2.5 μM or 5 μM heme. Data represent means ± standard error of the mean. *P < .05 vs control group; **P < .01 vs control group.