Heme oxygenase-1 in lesions of rat experimental autoimmune encephalomyelitis and neuritis.

The enzyme heme oxygenase-1 (HO-1) is reducing heme to the gaseous mediator carbon monoxide, to iron and the antioxidant biliverdin. The inducible expression of HO-1 is considered a protective cellular mechanism against reactive oxygen intermediates. Further, carbon monoxide (CO) is a regulator of cGMP synthesis, of NO-synthetases and cyclooxygenases, thereby indirectly modulating reactive processes. Here we report expression of HO-1 in rat experimental autoimmune encephalomyelitis (EAE) and neuritis (EAN). With both models, similar results were obtained: HO-1 was localized predominantly to infiltrating, monocytic, but only rarely to ramified microglial cells or astrocytes surrounding the inflammatory lesions. Prominent expression by monocytic cells was seen from day 11 after immunization correlating with the development of neurologic disease. Further, local expression is persistent for long after cessation of neurologic signs. Thus, HO-1 could be considered a factor in the formation and resolution of inflammatory autoimmune lesions of the nervous system.