Accelerated S. aureus–induced skin infection in FXII-deficient mice is rescued by human FXII. WT, F12^−/− mice, and F12^−/− mice reconstituted once with a dose of 2 µg human FXII per gram of body weight (F12^−/−+FXII) were injected subcutaneously with 1 × 10⁹ CFU S. aureus bioluminescent strain Xen29 (n = 10 per group). (A) Representative S. aureus in vivo bioluminescence on a pseudocolor scale overlaid on top of a greyscale image of WT, F12^−/−, and F12^−/−+FXII mice. (B) Bacterial counts as measured by in vivo bioluminescence of S. aureus demonstrated as mean total flux (photons per second) in a logarithmic scale. (C) Mean total size of the skin lesion in cm² ± SEM. (D–G) Bacterial burdens observed in kidneys (D), spleens (E), lungs (F), and livers (G) of WT, F12^−/−, and F12^−/−+FXII mice at day 5 after infection. Values are CFUs ± SEM within the entire organ as determined by serial dilutions of tissue homogenates. *P < 0.05 and **P < 0.01 versus WT (B and C) or F12^−/− (D–G). P values were determined using Student’s t test (B and C) or one-way ANOVA (D–G).