Infiltration of innate immune cells into the muscle after injury.

<p><b>(A)</b> At indicated time points after injury or sham treatment, digested tissues of the gastrocnemius muscles were stained with fluorescent antibodies against Gr-1, CD11b, and CD11c. Region I depicts CD11c⁺Gr-1^– cells, and region II depicts Gr-1⁺CD11c^– neutrophilic granulocytes. Monocytes/macrophages (mono/mac) were identified as CD11b⁺ cells (region IV) among gated CD11c^–Gr-1^– total muscle cells (region III). Numbers indicate the percentage of gated cells. The dot plots from sham-treated muscle are representative of dot plots from all sham-treated muscles at any time point. The dot plot for the isotype control is shown for time point 4d after injury and is representative for muscles from sham and injured mice at any time point. <b>(B)</b> The absolute number of granulocytes, monocytes/macrophages, and CD11c⁺ cells per muscle was determined. Median (horizontal lines), 25^th to 75^th percentile (extension of boxes), and range (error bars) of n = 6–8 mice per group are shown. Asterisks indicate statistically significant differences that were detected with the Kruskal-Wallis test followed by Dunn’s post hoc test. <b>(C)</b> Localization of granulocytes in the skeletal muscle 24 h after sham treatment or injury. Representative sections of skeletal muscle underwent immunofluorescent staining against Gr-1 (green) and laminin-2 (red) and were examined using laser scanning microscopy as described in Materials and Methods. Nuclei are visualized in blue. Scale bar = 50 μm **, p <0.01; ***, p <0.005 sham treatment vs. injury. iso, isotype.