HIMF enhances Flk-1 expression in mouse lungs. Recombinant HIMF protein or BSA was intratracheally instilled into adult mice (200 ng/animal in 40 μl saline, n = 3 for each group). The vehicle controls were instilled with saline (40 μl/animal, n = 3). Twenty-four hours later, the mouse lungs were collected. (A) Immunohistochemical staining results indicated that instillation of HIMF protein, but not BSA, resulted in a significant increase of Flk-1 production, mainly located at endothelial cells of the alveolar capillaries (arrows). However, the Flk-1 staining is very weak in the alveolar septa and strong signal is only found in vascular endothelial cells (v) in both saline and BSA controls (arrows). Scale bars: 100 μm. (B) Western blot with proteins from lung homogenates indicated that Flk-1 expression was enhanced in HIMF-, but not in saline- or BSA-instilled mouse lungs. The symbol (*) indicates a significant increase from control mouse lungs instilled with saline only (P < 0.05).