Fig. 7: Mesothelial EGFR expression of human patients with bacterial peritonitis is increased.

a–d Biopsies from human patients. Patients either underwent surgery due to acute appendicitis (c, d) or for elective abdominal surgery such as tumor surgery (a, b). Formalin fixed and paraffin-embedded samples were stained with anti-human epidermal growth factor receptor (EGFR), anti-human cytokeratin and anti-human calretinin. (a) and (c) both show an overview. Scale bar: 5 mm. (b) and (d) show magnifications of (a) and (c) respectively, Scale bar: 20 µm. e Mean EGFR expression was quantified in all patients. Outlier in red color represents an elective-surgery case that turned out to be a perforated tumor with potential bacterial contamination (not excluded for statistical testing). P = 0.00075. f Automated quantification of mesothelial cell roundness. P = 0.00013. g Linear regression shows a correlation between mean mesothelial EGFR expression and mean mesothelial roundness (R² = 0.68, p < 0.0001). h Area with suspected appendiceal adhesion covered up with granulation tissue. Magnification shows the abundance of EGFR positive cells in granulation tissue. Scale bar: 100 µm. The images shown in (a–d) are representative of the quantification shown in (e–f). The images shown in (h) are representative of the appendicitis group of patients. Data are presented as mean and individual symbols. Data are representative of n = 7 for Elective and n = 11 for Appendicitis group. Patient demographics according to Supplementary Table 1. Indicated statistical differences in (e) and (f) by Wilcoxon test (two-sided). R-squared and p-value in (g) by linear regression. Source data are provided as a Source Data file. ***P < 0.001. OD: optical density.