Polymorphonuclear myeloid-derived suppressor cells protect against hyperoxia-induced bronchopulmonary dysplasia in neonatal mice through suppression of excessive inflammatory response.

Background: Bronchopulmonary dysplasia (BPD), which primarily affects premature infants, is characterized by impaired lung development, reduced alveolarization, and chronic inflammation, leading to long-term respiratory complications. However, clinical prevention treatment of BPD remains challenging. Because immune cells may have a role in BPD pathogenesis and prevention, we investigated whether polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) protect against hyperoxia-induced BPD in a neonatal mouse model.

Methods: Neonatal C57BL/6 mice were exposed to either normoxia (21 % oxygen) or hyperoxia (85 % oxygen) since birth. Lung development was analyzed on postnatal days 3, 7, and 14 by using histological techniques [hematoxylin and eosin (H&E) staining and radial alveolar count (RAC) measurement]. Moreover, we used flow cytometry to identify lung myeloid-derived suppressor cell (MDSC) subsets. PMN-MDSCs' therapeutic potential at key developmental stages was evaluated through adoptive transfer experiments. PMN-MDSC transplantation outcomes in the lung tissues were assessed through histological analysis, immunofluorescence staining for alveolar and vascular markers, and proinflammatory cytokine measurement.

Results: Hyperoxia-exposed mice exhibited considerable lung damage, including enlarged and irregular alveoli, low RACs, and decreased body weights compared with normoxic controls. Hyperoxia reduced PMN-MDSC numbers but increased monocytic MDSC numbers. PMN-MDSC transplantation preserved alveolar structure and increased alveolar and pulmonary vessel numbers. Immunofluorescence staining confirmed enhanced alveolar and vascular development. Finally, PMN-MDSCs reduced proinflammatory cytokine levels in lung tissues.

Conclusions: PMN-MDSCs may protect against hyperoxia-induced lung injury by promoting alveolar and vascular development and reducing inflammation in neonatal mice. Further research elucidating precise mechanisms underlying the protective effects of PMN-MDSCs and their potential for clinical translation is warranted.