Lyn knockout mice have increased lung microvascular endothelial permeability and higher mortality rate in response to LPS challenge. (A) The lung capillary filtration coefficient (K_f,c) was determined in Lyn^+/+ and Lyn^−/− mice before or at 6 hours after administration of LPS (5 mg/kg body weight). Bars indicate means ± standard error (n = 5). P < .005 and .001 between wild-type littermates and Lyn^−/− mice under control or LPS administration, respectively, by unpaired 2-tailed Student t test. P < .05 by Bonferroni correction analysis of multiple comparisons. (B) Kaplan-Meier survival plots for Lyn^+/+ (WT) and Lyn^−/− (Lyn^−/−) mice. Mice were challenged with LPS (12 mg/kg) via intraperitoneal injection. The percentage of surviving animals was 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). (C) Lung microvascular permeability in Lyn^+/+ and Lyn^−/− mice before or at 6 hours after challenging with VEGF (3 μg/kg body weight). Bars indicate means ± standard deviation (SD; n = 6). P values indicated in the figure were analyzed by unpaired 2-tailed Student t test. P < .05 by Bonferroni correction analysis of multiple comparisons. (D) Lung microvascular endothelial cells isolated from Lyn^−/− and wild-type littermates were cultured and solubilized, and Lyn, c-Src, and Fyn in cell lysates were detected by western blot. β-actin was detected by western blot with mouse monoclonal antibody (Sigma) to verify equal loading. (E) VEGF in plasma from Lyn^−/− and wild-type littermates was measured by enzyme-linked immunosorbent assay (ELISA) assay with a VEGF ELISA kit (Sigma). Difference was assessed using unpaired 2-tailed Student t test, P > .5. Values are means ± SD (n = 3).