*Article* **Effect of Heme Oxygenase-1 Depletion on Complement Regulatory Proteins Expression in the Rat**

**Maria G. Detsika 1,\*, Eirini Theochari 2, Kostas Palamaris 2, Harikleia Gakiopoulou <sup>2</sup> and Elias A. Lianos <sup>3</sup>**


**Abstract:** Heme oxygenase has been implicated in the regulation of various immune responses including complement activation. Using a transgenic rat model of HO-1 depletion, the present study assessed the effect of HO-1 absence on the expression of complement regulatory proteins: decay accelerating factor (DAF), CR1-related gene/protein Y (Crry) and CD59, which act to attenuate complement activation. Protein expression was assessed by immunohistochemistry in kidney, liver, lung and spleen tissues. DAF protein was reduced in all tissues retrieved from rats lacking HO-1 (*Hmox1*−/−) apart from spleen tissue sections. Crry protein was also reduced, but only in *Hmox1*−/<sup>−</sup> kidney and liver tissue. C3b staining was augmented in the kidney and spleen from *Hmox1*−/<sup>−</sup> rats, suggesting that the decrease of DAF and Crry was sufficient to increase C3b deposition. The observations support an important role of HO-1 as a regulator of the complement system.

**Keywords:** complement; heme oxygenase (HO)-1; complement regulatory proteins
