Complement C5a/C5aR1 axis is a key inflammatory pathway, unleashed upon HO-1 inhibition and treatment with heme. (A) Plasma (C5a; measured by ELISA). (B-E) C5aR1 gene expression measured by QuantiGene in liver (B), heart (C), kidney (D), and lung (E). C5a is powerful anaphylatoxin generated after complement cascade activation, which signals through its main receptor C5aR1 on a variety of cells, mainly neutrophils, inflammatory monocytes, macrophages, and endothelial cells. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001. ns, not significant.