Introduction Inflammation in chronic obstructive pulmonary disease (COPD) is associated with increased numbers of highly activated macrophages with a reduced phagocytic capacity. Macrophages may exist as M1 “classically activated” or M2 “alternatively activated” with different phagocytic and inflammatory mediator profiles, suggesting in COPD a more persistent, M1 macrophage predominates. It is unknown whether circulating monocytes in COPD patients predetermine whether M1 macrophages will be preferentially activated, thus driving an inflammatory phenotype.
Objectives This study investigated differences between monocyte-derived macrophages (MDM) from non-smokers, smokers and COPD patients driven towards M1and M2 phenotypes.
Methods Monocytes were isolated from whole blood and cultured with GM-CSF (2 ng/ml) or M-CSF (100 ng/ml) for 12d to generate M1 and M2 MDM respectively. Cells were stimulated with LPS (0.01–100 ng/ml) for 24 h and TNFα, CXCL8 and IL-10 measured by ELISA. Phagocytosis was measured fluorimetrically following exposure to fluorescent beads, H influenzae or S pneumoniae for 4 h.
Results There were no differences in baseline release of any of the cytokines measured between subject groups. Cells released cytokines in response to LPS in a concentration-dependent manner. M1MDM derived from non-smokers and COPD patients released greater concentrations of LPS-stimulated (10 ng/ml) TNFα compared to M2 MDM. (Non-smokers: 7.4±2.3 vs 1.5±0.2 ng/ml, n=4; p<0.01; COPD: 7.0±1.8 vs 2.1±0.9 ng/ml, n=4) and significantly less IL-10 (Non-smokers: 0.4±0.2 vs 3.0±0.6 ng/ml, n=4; p<0.05; COPD: 0.3±0.04 vs 1.5±0.5 ng/ml, n=3) than M2 MDM. These differences were not apparent in cells from smokers. Both M1 and M2 MDM released LPS-stimulated CXCL8 similarly with no difference between subject groups. Phagocytosis of polystyrene beads was similar by both MDM phenotypes in all subject groups. However, there was a trend for M2 MDM to phagocytose more bacteria compared with M1 MDM which reached significance in healthy subjects (p<0.05).
Conclusions M1 and M2 MDM from non-smokers and COPD subjects showed distinct differences with respect to LPS-stimulated cytokine release and phagocytosis, however these differences were not apparent in cells from smokers without COPD. This suggests that smokers without COPD have altered circulating monocytes that do not differentiate into the pro-inflammatory M1 macrophage and may be protective against the development of COPD.
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