Endothelial Lyn contributes to increased lung permeability and higher mortality rate of Lyn^−/−mice in response to LPS challenge. (A) Expression of Lyn in bone marrow cells from Lyn^+/+ (WT→WT, n = 5) and Lyn^−/− (WT→ Lyn^−/−, n = 6) mice repopulated with Lyn^+/+ donor bone marrow cells was detected by western blot with a rabbit polyclonal antibody against Lyn. Bone marrow cells from a Lyn^−/− mouse were used as a control. β-actin was detected by western blot with mouse monoclonal antibody (Sigma) to verify equal loading. (B) Expression of Lyn in bone marrow cells from wild-type mice repopulated with Lyn^−/− donor bone marrow cells was detected by western blot with a rabbit polyclonal antibody against Lyn. Bone marrow cells from a wild-type and Lyn^−/− mouse were used as controls. β-actin was detected by western blot with mouse monoclonal antibody to verify equal loading. (C) Lung microvascular permeability in Lyn^+/+ and Lyn^−/− mice repopulated with either Lyn^+/+ or Lyn^−/− donor bone marrow cells was measured. In some experiments, Lyn^−/− mice repopulated with Lyn^+/+ donor bone marrow cells were injected with LPS. Six hours after LPS injection, lung microvascular permeability was measured. Bars indicate means ± SD (n = 5∼7). (D) Wild-type and Lyn^−/− mice repopulated with wild-type donor bone marrow cells were challenged with LPS (8 mg/kg) via intraperitoneal injection. Survival rates were observed at 24, 48, 72, 96, and 120 hours after LPS injection. The difference in survival between WT and Lyn^−/− mice was significant (P < .001).