Midkine is a retinoic acid-responsive, heparin binding growth factor expressed in various cell types including lung during embryogenesis. In vitro and in vivo studies demonstrated that midkine promotes angiogenesis, cell growth, cell migration and growth of the pulmonary mesenchyme during branching morphogenesis of embryonic lung but its role and expression pattern in lung in general is still unknown. In this study; cytokine and midkine expression responses of rat lung in a pneumonia model that is produced by intratracheally instilled with Klebsiella pneumoniae suspension was evaluated. Rats were exposed to 10% O2. Lung tissue midkine, TNF-a, IL-6, IL-10 levels were measured by ELISA. Midkine expression was evaluated immunohistochemically. Midkine expression was more prominent in bronchiole epithelial nucleus in healthy rats. TNF-a, IL-6 and midkine levels increased in K.pneumoniae infected rat lungs, whereas IL-10 levels were found decreased. Hypoxia and dexamethasone suppressed proinflammatory cytokine and midkine secretion responses in infected rat lungs. Midkine levels correlated with TNF-a levels. Our results showed that adult rat lung has basal midkine secretion, which was induced more by bacterial infection.

This study was supported by TUBITAK-BMBF (SBAG108S262).