Hx protects macrophages from heme overload. (A-B) Heme content in the spleen and in splenic myeloid cells (CD11b⁺ granulocytes, monocytes, and ferromagnetic macrophages) from untreated (NT) and heme-treated (+heme) (hemin 70 μmol/kg; 1 hour after injection) wild-type (Wt) and Hx-null (Hx^−/−) mice (n = 3). (C-G) HO-1, L-ferritin, and FPN mRNA and protein expression in splenic myeloid cells (granulocytes, monocytes, and macrophages) isolated from the spleen of untreated (NT) or heme-treated (hemin 70 μmol/kg; 6 hours after injection) wild-type and Hx-null mice. In C and F, HO-1 and FPN mRNA levels were analyzed by qRT-PCR (NT: n = 5; heme: n = 6). Representative western blots of HO-1, L-ferritin, and FPN are shown in D, E, and G (NT: n = 3; heme: n = 6). (H) qRT-PCR analysis of IL-6 mRNA expression in splenic myeloid cells isolated from the spleen of untreated (NT) or heme-treated wild-type and Hx-null mice (hemin 70 μmol/kg; 6 hours after injection) (untreated, NT: n = 3; heme: n = 6). Values represent mean ± SEM. *P < .05; **P < .01; ***P < .001. mRNA levels measured by qRT-PCR are expressed in relative quantity (RQ) to the untreated (NT) sample (RQ = 1); densitometric analysis is reported in arbitrary units (AUs), as the ratio to the untreated (NT) sample (AU = 1).