Fig. 4

Establishment of the murine metritis model system and mMSC therapy. Imaging of intrauterine transcervical infusion (A-B). E. coli strain 8-3B43/pKB4985 mCherry expressing bacteria originally isolated from a natural case of clinical post-partum bovine metritis in a dairy cow (C). Comparative growth curves in LB of utero pathogenic (8-3B43 and 22-0B1) and mammary pathogenic (P4 and P4-NR) E. coli strains (D). Bacterial colonization observed following E. coli challenge was significantly reduced by MSC treatment of challenged mice (E). Metritis was scored (F) using H&E stained sections (G-J). Metritis is characterized by massive infiltration of neutrophils into the endometrium and lumen (black arrows in G-H and yellow arrow in I). Representative images of fluorescence staining using DAPI (blue) phalloidin (cyan in H and red in I), anti-murine CD45 antibodies (red in I), anti-murine Ly6G (green in I). Fluorescing mCherry bacteria interacting with luminal neutrophils and endometrial epithelial cells are visible in (J). Some challenged mice were also treated with mMSCs and disease was evaluated by metritis score (F). In scatter plots (E and F), each data point represents a single uterine horn and each experimental group was compared to the normal control group. Statistical significance was determined by non-parametric Mann–Whitney two-independent-samples test using GraphPad Prism 6 (GraphPad Software, Inc.) and P value of 0.05 or less was considered significant. Scale bars; 200 µm (G), 50 µm (H-I) and 20 µm (J). Figure (A) was created with BioRender.com