Lack of macrophage Fpn1 diminishes the hypoferremic response to LPS. Sex-matched 2-month-old Fpn1^flox/flox and Fpn1^LysM/LysM mice were injected intraperitoneally with LPS at 5 μg per gram of body weight. After LPS injection, the animals were killed at the times indicated, and tissue and blood were harvested for analysis. (A-D) Serum iron (A), UIBC (B), total iron-binding capacity (TIBC; C), and transferrin saturation (D) were measured at 0, 3, and 24 hours after injection with LPS. (E) Spleen nonheme iron concentrations. (F) Total nonheme iron content in the spleen (n = 6 per group). (G) Liver nonheme iron concentrations. (H) Relative Hamp1 mRNA levels in the liver of Fpn1^flox/flox and Fpn1^LysM/LysM mice were measured by quantitative RT-PCR. Results were normalized to the internal control β-actin and presented as relative expression level calculated by the 2^ΔΔC_t method. Data are mean ± SEM. (I) Serum IL-6 concentrations measured 0, 1.5, and 3 hours after LPS treatment. (J) Serum TNF-α concentrations measured 0, 1.5, and 3 hours after LPS treatment. Data are mean ± SEM; n = 6 per group (3 male, 3 female). *P < .05. †P < .001.