Fig. 4

Improvement of lung barrier function by Vasculotide (VT) was associated with diminished edema formation. Streptococcus pneumoniae (5 × 10⁶ colony-forming units/mouse) or sham-infected mice were intravenously (i.v.) treated with VT (500 ng) or PBS 22 h, 34 h, and 46 h postinfection (p.i.). Lungs were prepared, and bronchoalveolar lavage was performed 24 h or 48 h p.i. Human serum albumin (HSA) was i.v. administered 23 h or 47 h p.i., and HSA bronchoalveolar lavage fluid (BALF)/plasma ratio was determined by enzyme-linked immunosorbent assay to quantify permeability. For histological analysis, lungs were prepared and fixed 24 h or 48 h p.i. a and b Lung permeability was decreased 24 h and 48 h p.i. upon VT treatment. c Histological analysis revealed that infected and PBS-treated mice showed massive perivascular edema formation 24 h after infection (asterisks), which was considerably reduced by VT treatment. d At 48 h p.i., the edematous perivascular spaces in the lungs were increasingly infiltrated by neutrophils (asterisks), but without differences between the VT-treated and untreated infected groups. In the sham-infected groups, no edema formation or other pathological changes could be seen in the perivascular spaces at both time points (arrows in c and d). e PBS-treated mice showed massive alveolar edema formation 48 h after infection (asterisks), which was almost completely abolished (three of four mice) by VT treatment. f and g Semiquantitative determination of perivascular (f) and alveolar (g) edema formation confirmed these observations. a and b Values are given as mean + SEM (n = 8 for S. pneumoniae-infected groups or n = 5 for sham-infected groups). **p < 0.01 between indicated groups. c, d, and e Representative images are shown (n = 3–4); n.p. not present. Bars = 100 μm (c, d), 50 μm (e). f and g Values are given as mean + SEM (n = 3–4)