Fig. 1

Osteopontin prevents acute lung injury caused by extracellular histones. a Survival curves of wild-type (WT) and osteopontin (OPN)^−/− mice after intranasal instillation of calf thymus histones (CTH; 50 µg/g of body weight). Survival was monitored for 7 days (only the course during the first 72 h is shown in the figure). n = 6 per group; ***P = 0.0007 between groups. b Survival curves of OPN^−/− mice after intranasal instillation of CTH in buffer alone or together with recombinant mOPN. The survival was monitored for 7 days (only the course during the first 72 h is shown in the figure). n = 8 per group; ***P = 0.0007 between groups. c Survival curves of WT mice after intravenous injection of CTH (75 µg/g of body weight) in buffer alone or together with OPN (100 µg/mice). The survival was monitored for 24 h (only the course during the first 2 h is shown in the figure). n = 4 per group; **P = 0.0069 between groups. d The concentrations of OPN in the bronchoalveolar lavage fluid (BALF) of WT mice 0, 4, 8, and 16 h after instillation of CTH. n = 6 per group; *P = 0.002, ****P < 0.0001 between groups. e, f To assess lung injury, lactate dehydrogenase (LDH; reflecting cytotoxicity) and alveolar albumin (reflecting capillary leakage) levels were determined in BALF using ELISA after histone-induced lung injury in WT and OPN^−/− mice, respectively. n = 8 per group; ****P = < 0.0001, **P = 0.0022 between groups. g The levels of AST in plasma were assessed in order to reflect the effects on overall organ damage following histone-induced lung injury. n = 6 per group; *P = 0.035 between groups. h A blinded evaluation of the tissue injury was performed on hematoxylin & eosin-stained slides using a lung injury scoring system, showing increased lung injury in OPN^−/− mice. n = 6 per group; **P = 0.0022 between groups. i Representative hematoxylin & eosin staining and scanning electron microscopy images of lung sections, showing differences in lung damage when comparing WT and OPN^−/− mice, as indicated on each panel. Scale bars = 100 μm. j Heat map representation of cytokine profiles in BALF of WT and OPN^−/− mice after histone-induced lung injury. Inflammatory mediators were measured using multiplex bead assay 16 h after intranasal instillation of CTH. k Bar graph representation of selected key pro-inflammatory mediators. Data are mean ± SEM; n = 9 per histone-exposed group, n = 5 per control group