Time course of cigarette smoke-induced pulmonary inflammation in mice

Matrix Metalloproteinase-12 and Cathepsin D Expression in Pulmonary Macrophages and Dendritic Cells of Cigarette Smoke-Exposed Mice

An imbalance between proteinases and their inhibitors is believed to play an essential role in the development of chronic obstructive pulmonary disease (COPD) and pulmonary emphysema. COPD is mainly caused by cigarette smoking, and is characterized by an increase in inflammatory cells in small airways and lung parenchyma. We examined the mRNA expression of several proteinases in lungs of mice exposed to cigarette smoke or control air. After 1, 3 and 6 months' smoke exposure there was a significant increase of matrix metalloproteinase (MMP)-12 and Cathepsin D mRNA, compared to air-exposed mice. To determine the cellular origin of MMP-12 and Cathepsin D, we isolated dendritic cells (DCs) and macrophages from the lungs of mice. There was an increase in MMP-12 mRNA after smoke exposure in both macrophage and DC populations, whereas Cathepsin D was predominantly expressed in macrophages. Immunohistochemistry clearly revealed the expression of Cathepsin D protein in alveolar macrophages of cigarette smoke-exposed mice, in contrast to air-exposed littermates. Western blots on lung tissue demonstrated an increase of MMP-12 protein in cigarette smoke-exposed animals. These results indicate that cigarette smoke increases the expression of MMP-12 and Cathepsin D in the lungs of mice, and that not only macrophages but also DCs produce MMP-12.

Pulmonary dendritic cells

Dendritic cells (DCs) are leukocytes that are emerging as chief orchestrators of immune responses. The crucial task of DCs is the continuous surveillance of antigen-exposed sites throughout the body, and their unique responsibility is to decide whether to present sampled antigen in an immunogenic or tolerogenic way. Any misstep can either lead to a flawed immune defense or to allergy, even autoimmunity. It comes as no surprise that the lungs become increasingly the subject of DC-related investigations, as they represent a vast interface between the body and the outer world. This constitutes an enormous challenge for the immune system: "firing up" immune responses inappropriately could have devastating results for the fragile gas exchange structures. Evidence accumulates that DCs play a pivotal role in maintaining the delicate balance between tolerance and active immune response in our respiratory system. The exponentially growing body of DC-related publications is a big challenge. This article aims to provide researchers and clinicians with an up-to-date view on DC biology and its relevance to pulmonary medicine. A developing trend in the field of DCs is the shift from fundamental immunologic research toward exciting clinical insights and applications. For the pulmonary clinician, this heralds the dawn of promising therapies in various domains such as infections, allergy, and cancer.