Monocyte sub-populations do not reflect differences in COPD macrophage phenotype

Human monocytes are characterised by expression of CD14 and CD16 into classical CD14⁺⁺CD16^- (Cθ), intermediate CD14⁺⁺CD16⁺ (Iθ) or non-classical CD14⁺CD16⁺⁺ (NCθ) subsets. Monocyte subsets may affect subsequent macrophage phenotype and hence be important in COPD. Peripheral blood monocytes from non-smokers (NS N=10), smokers (S N=8) and COPD patients (COPD N=8) were analysed by flow cytometry for CD14 and CD16 expression, or differentiated in either GM-CSF (GΦ) or M-CSF (MΦ) to create distinct monocyte-derived macrophages. Macrophages were analysed based on their LPS-stimulated TNFα output and phagocytosis of <i>S.pneumoniae</i> (SP). There was no difference in % monocyte subset distribution between subject groups; <b>Cθ</b> NS: 75±2, S: 73±5, COPD: 72±4, <b>Iθ</b> NS: 12±1, S: 11±2, COPD: 14±5, <b>NCθ</b> NS: 4±1, S: 4±1, COPD: 5±1. NS MΦ phagocytosed 230% more SP compared to NS GΦ (p&lt;0.001), 125% more in S MΦ (p&lt;0.01) and 60% more in COPD MΦ compared to their GΦ equivalents. There was a significant difference in LPS-induced-TNFα between NS GΦ (6±1ng/ml) and NS MΦ (1.7±0.1ng/ml) (p&lt;0.01). This difference was reduced when comparing S GΦ (7±1ng/ml) to S MΦ (3±0.4ng/ml), and even further when comparing COPD GΦ (8±2ng/ml) to COPD MΦ (7±2ng/ml). Although no differences were seen in monocyte subsets, there were significant functional differences between GΦ and MΦ. COPD Φ also showed hyper-inflammation and impaired phagocytosis regardless of their differentiation conditions. These data suggest that differentiation, not monocyte subset, dictates differences in macrophage phenotype and that this process is altered in COPD, generating dysfunctional macrophages.