EPO and bronchopulmonary dysplasia: Hematoxylin and eosin-stained sections of lung tissue demonstrated that alveolar structure was markedly abnormal after neonatal mice were exposed to high oxygen for 14 days (Figure 1B), furthermore, degree of alveolarization measured by radial alveolar counts (Figure 1C) and alveolar septum thickness (Figure 1D) were significantly improved in the MSCs, EPO and MSCs+EPO groups compared with BPD group, especially in the MSCs+EPO group (P < 0.05).