Subcutaneous infection of wild-type and fXIII^−/− mice with S pyogenes. H&E–stained representative tissue sections from noninfected (A-B) and infected (24 hours after infection; C-D) wild-type (A,C) and fXIII^−/− (B,D) mice are shown. Infected animals show signs of inflammation (white arrows) and tissue damage (black arrows). The scale bar indicates 500 μm. Giemsa-stained biopsies from the inflamed area of wild-type (E) and fXIII^−/− mice (F) are shown. Arrowheads point to infiltrating inflammatory cells (macrophages/neutrophils). The scale bar indicates 25 μm. Scanning electron micrographs depict biopsies from wild-type (G) and fXIII^−/− (H) mice. Arrows indicate bacteria entrapped and clustered within the fibrin meshwork in wild-type mice (G) and scattered throughout the infection area in fXIII^−/− animals (H). Scale bars indicate 10 μm in the figure and 1 μm in the insets. (I) aPTT measured in plasma from noninfected and infected wild-type and fXIII^−/− mice (24 hours after infection). Data are presented as mean values of plasma samples obtained from 3 or 5 noninfected and 9 infected animals obtained from 3 independent experiments. *P < .05; **P < .01.