Modulation of dendritic cells by human neutrophil elastase and its inhibitors in pulmonary inflammation

Abstract

Dendritic cells (DC) are sentinels of the immune system that display an extraordinary capacity to present antigen to naïve T cells and initiate immune responses. DCs are distributed throughout the lungs in the conducting airways of the tracheobronchial tree and in the parenchymal lung, and play a pivotal role in controlling the immune response to inhaled antigens. The respiratory surface is continually exposed to potentially injurious particulates and pathogenic organisms, to which tightly regulated innate and adaptive immunological responses are made. The airways are usually sterile in healthy individuals. However, patients with chronic obstructive pulmonary disease (COPD) and cystic fibrosis (CF) have increased susceptibility to microbial infections and increased neutrophil elastase (NE) in lung secretions. This thesis was designed to test the hypotheses that; (i) excess NE may result in a dysregulation of lung DCs function in pulmonary chronic diseases, and (ii) the natural NE inhibitors in the respiratory system are able to rescue the NE-mediated dysregulation of DCs and potentially enhance their antigen presenting activity. The data in this thesis demonstrate that purified human NE down-regulated murine bone marrow (BM)-derived DC co-stimulatory molecules (CSM; CD40, CD80 and CD86), which was due to its proteolytic activity. NE-treated LPS-matured DCs were less efficient at presenting ovalbumin (OVA) peptide to naïve OVAspecific transgenic (D011.10) T cells. In addition, immature DCs (iDC) simultaneously treated with LPS and NE failed to mature fully and produced significantly less IL-12 and TNF-α than DCs matured in the presence of LPS alone. Similarly, treatment of mature DC (mDC) with pooled and individual COPD and CF sputum samples caused a reduction in CD80 and CD86 levels (but not CD40) which positively correlated with the NE concentration present in the samples. The demonstration that NE could adversely affect DC phenotype and function suggested that augmentation of NE inhibitors could reverse this process and preserve DC function in inflammatory microenvironments. Over-expression of an NE specific inhibitor (elafin) in the lungs of mice (using either replication-deficient adenovirus [Ad] or elafin transgenic [eTg] mice) increased the number (immunofluorescence) and activation status (flow cytometric measurement) of CD11c+/MHCII+ lung DCs in in vivo models. Replication-deficient Ad vectors encoding NE inhibitors, namely elafin, secretory leukocyte protease inhibitor (SLPI) and α1-protease inhibitor (α1-PI), were also used to infect DCs in vitro, to further study the effect of these NE-inhibitors on DCs in isolation. These findings suggest that purified NE and NE-containing lung inflammatory secretions are powerful down-regulators of DC maturation, resulting in reduced capacity of these potent APCs to efficiently present antigens; whereas, NE inhibitors could boost immunity by increasing the activation state and/or number of DCs.