Role of HO-1 and CO on DC activation. BM-DCs were cultured for 24 hours with the graded concentrations of CoPPIX (A) or CORM-2 (B) in the presence of LPS (●) or vehicle alone (○). The culture supernatants were examined for the indicated cytokines. The cell viability was examined by PI uptake (mean ± SD, n = 3). (C) BM-DCs were pretreated for 1 hour with hemoglobin at the indicated concentrations, and then cultured for 24 hours with LPS in the presence of CoPPIX (left panel) or CRA (right panel; mean ± SD, n = 3). Asterisks indicate statistically significant (*P < .05; **P < .01) differences compared with the nontreated control samples.