-induced liver injury and liver recovery after UCMSCs transplantation. (A) Haematoxylin and eosin stain. After 24 hours from CCl4 injection confluent coagulative submassive necrosis affected 43.3% of the liver. The margins of representative necrotic area (N) are indicated by arrows. (B) Haematoxylin and eosin stain. After 5 days from CCl4 administration the necrotic area (N, indicated by arrows) was still wide and there was a conspicuous inflammatory infiltrate. After 8 days there were not necrotic areas and numerous cellular clusters were evident (head arrows). See Additional file 1: Figure S1 for higher magnification. UCMSCs transplantation in CCl4-treated mice reduced the amount of inflammatory cells and necrosis area after 5 days. Necrosis, inflammatory recruited cells and cellular cluster were completely absent after 8 days and histological pattern was becoming similar to control healthy mice parenchyma (see Additional file 2: Figure S2). (C) Necrosis quantification at day 5. Scale bar: 100 μm.