Hypoxia-preconditioned mesenchymal stem cell transplantation downregulates expression of inflammatory factors in the bleomycin-induced pulmonary fibrosis mouse model. Quantitative real-time RT-PCR was performed to analyze the expression of inflammatory factors (A) interleukin (IL)-6 and (B) pro-IL-1β in the lung tissues of animals that received normoxia-preconditioned mesenchymal stem cells (NP-MSCs), hypoxia-preconditioned mesenchymal stem cells (HP-MSCs) or phosphate-buffered saline (PBS) for 18 days following bleomycin (BLM) administration on day 3. Values are normalized to the GAPDH values and expressed relative to the PBS group. *P < 0.05, **P < 0.01. Each dot represents an individual mouse with the mean shown for n > 5 per group. (C) Western blot analysis of pro-IL-1β and IL-1β in whole lung tissues from each group. Ctrl, control.