HO-1 (haem oxygenase-1) is a stress-inducible enzyme that plays a protective role in inflammation. Pro-inflammatory mediators, including lipopolysaccharide and cytokines, induce HO-1 expression. The 5'-flanking region of the HO-1 gene contains binding sites for the transcription factors that regulate inflammation, including nuclear factor-kappaB and activator protein 1. However, these do not appear to mediate lipopolysaccharide-induced HO-1 gene expression. in response to haem and antioxidants, murine HO-1 is regulated by the transcription factor Nrf2 (NF-E2-related factor 2). This transcription factor may also be important in the regulation of HO-1 by pro-inflammatory stimuli.