Role of interleukin-6 in elastase-induced lung inflammatory changes in mice

Interleukin-6 (IL-6) is known to be involved in the pathogenesis of various inflammatory diseases, but its role in the development of pulmonary emphysema remains unclear. Wild-type (WT) and IL-6-deficient mice received either phosphate-buffered saline (PBS) or porcine pancreatic elastase (PPE) intratracheally. The development of emphysema was determined by measuring the mean linear intercept (Lm). The lung specimens were also subjected to immunohistochemistry for single-stranded DNA to detect apoptotic cells. Lung mechanics and airway responsiveness to inhaled methacholine were analyzed. Bronchoalveolar lavage (BAL) fluid was subjected to evaluation of inflammatory cell accumulation and cytokine measurement. PPE treatment caused significant increases in Lm and lung compliance, which was attenuated by IL-6 deficiency. The increases in apoptotic cells in the lung were attenuated in IL-6 null mice. Airway responsiveness was not affected by PPE challenge or IL-6 deficiency. Intratracheal PPE increased the cell counts in BAL fluid throughout the observation, which was suppressed in IL-6 null mice. In BAL fluid, PPE-induced increases in the levels of macrophage inflammatory protein (MIP)-1alpha and eotaxin were mitigated by IL-6 deficiency. PPE-induced up-regulation of matrix metalloproteinase (MMP)-12 in the lung was attenuated by IL-6 deficiency. These results indicate that IL-6 may play an important role in the development of elastase-induced lung inflammatory changes.