Defective S. aureus polyP-mediated fibrin formation and impaired fibrous abscess capsule integrity in F12 ^−/− mice. (A–H) WT, F12^−/− mice were subcutaneously inoculated with 3 × 10⁶ CFU S. aureus, and abscesses were removed 30 h after infection. Representative photographs of skin sections stained with (A–D) H&E or (E–H) fibrin-specific antibody 59D8 are shown. Dashed lines and black arrows denote abscess capsule and fibrin staining around the abscess, respectively. Scale bars represent 50 µm. (I) Quantification of fibrin staining given in % relative to WT mice. (J) Integrity of abscess capsule measured from immunohistochemistry sections by gaps within the discontinuous fibrin layer of the abscess capsule given relative to the abscess perimeter. (K) Number of S. aureus detected in the peripheral zone of the abscess given in relative to bacteria counts detected in WT mice, set to 100%. Images were analyzed with ImageJ software. Each symbol represents an individual animal. (L) PolyP was extracted from S. aureus by anion exchanger chromatography, separated on polyacrylamide/urea gel and visualized by DAPI-negative staining. Synthetic polyP with mean chain lengths of 39, 97, and 383 phosphate monomers served as molecular size standard. Purified polyP was loaded without and after incubation with PPX (10 U/ml for 2 h). A representative gel of n = 3 is shown. (M) Real-time thrombin generation in normal human plasma stimulated with S. aureus–derived polyP in the absence or presence of PPX_Δ12 (1 mg/ml). Plasma deficient in FXII (FXII def.) or FXI (FXI def.) and buffer-stimulated normal plasma was blotted for comparison. Representative thrombin generation curves of a series of n = 3. (N) Citrated whole mouse blood, readjusted to physiological Ca²⁺ and Mg²⁺ concentrations, was perfused over a surface coated with 3 × 10⁶ CFU S. aureus at a venous (100 s⁻¹) shear rate. Representative phase-contrast images of thrombi formed during perfusion of WT, F12^−/−, F11^−/−, or PPX_Δ12 -treated WT blood are shown. Surface covered area by all thrombi in % is given in the lower right corner. A representative experiment of n = 3 is shown. Source data are available for this figure: SourceData F4.