Fig. 3

Histopathological analysis of MSC–treated animals after K. pneumoniae infection. Lungs were harvested, fixed in formalin, and embedded in paraffin and 2 μm sections were prepared and stained with hematoxylin and eosin (a, b, d) or Giemsa (c) for histopathological analyses of MSC-treated versus mock-treated (NaCl) controls animals after K. pneumoniae infection (d2 p.i.). a K. pneumoniae induced suppurative and necrotizing pneumonia with a similar distribution of lung lesions in both groups. b, c Infected NaCl-treated controls showed severe suppurative and necrotizing pleuritis (b, arrowhead) and steatitis (c), admixed with myriads of bacteria, whilst MSC-treated animals displayed neither pleuritic, steatitis nor bacteria on the lung surface or in the mediastinal fat tissue. d In K. pneumoniae-infected NaCl-treated controls, neutrophils and histiocytes were predominantly located at the interstitium of the lungs (arrowhead) whereas in MCS-treated lungs, neutrophils were also present in alveolar spaces (arrowhead) consistent with suppurative bronchopneumonia. Representative images are shown (n = 3 experiments). Bar (a), 2 mm. Bar (b, d), 50 μm. Bar (c), 20 μm