Activation and polarization of circulating monocytes in severe chronic obstructive pulmonary disease

Abstract

Background: The ability of circulating monocytes to develop into lung macrophages and promote lung tissue damage depends upon their phenotypic pattern of differentiation and activation. Whether this phenotypic pattern varies with COPD severity is unknown. Here we characterize the activation and differentiation status of circulating monocytes in patients with moderate vs. severe COPD.

Methods: Blood monocytes were isolated from normal non-smokers (14), current smokers (13), patients with moderate (9), and severe COPD (11). These cells were subjected to analysis by flow cytometry to characterize the expression of activation markers, chemoattractant receptors, and surface markers characteristic of either M1- or M2-type macrophages.

Results: Patients with severe COPD had increased numbers of total circulating monocytes and non-classical patrolling monocytes, compared to normal subjects and patients with moderate COPD. In addition, while the percentage of circulating monocytes that expressed an M2-like phenotype was reduced in patients with either moderate or severe disease, the levels of expression of M2 markers on this subpopulation of monocytes in severe COPD was significantly elevated. This was particularly evident for the expression of the chemoattractant receptor CCR5.

Conclusions: Blood monocytes in severe COPD patients undergo unexpected pre-differentiation that is largely characteristic of M2-macrophage polarization, leading to the emergence of an unusual M2-like monocyte population with very high levels of CCR5. These results show that circulating monocytes in patients with severe COPD possess a cellular phenotype which may permit greater mobilization to the lung, with a pre-existing bias toward a potentially destructive inflammatory phenotype.

Keywords: COPD; Monocyte activation; Polarization; Systemic inflammation.

Conflict of interest statement

Ethics approval and consent to participate

The study was conducted in accordance with the amended Declaration of Helsinki. Institutional Review Board approval was obtained from the Temple University Institutional Review Board, and all subjects signed written informed consent.

Competing interests

The authors declare that they have no competing interests.

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Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures

Fig. 1

Representative flow cytometric analyses for PBMCs. Normal (a), smoker (b), moderate COPD (COPD-M) (c), and severe COPD (COPD-S) (d) were stained for expression of CD14 and CD16. Based on staining intensity, classical monocytes (CD14 + CD16-), intermediate monocytes (CD14 + CD16+), and non-classical monocytes (CD14DIMCD16+), as well as the total numbers of monocytes were identified

Fig. 2

The numbers of peripheral blood monocytes are significantly increased in severe COPD patients. The total number of blood monocytes (a), and the numbers of classical monocytes (b), intermediate monocytes (c) and non-classical monocytes (d) cells are presented. The percentages of classical monocytes and non-classical monocytes are also presented. The percentages of each population were determined relative to the total number of monocytes, and data are presented for the classical (e), non-classical (f), and intermediate (g) monocyte sub-populations. Data are presented as box plots with the mean (red line) and median (black line). The box delineates the interquartile range, and the vertical line represents the interquartile range. * = p < 0.05 and ** = p < 0.01 relative to the normal

Fig. 3

Altered composition of monocyte sub-populations in smokers and COPD patients. Classical (a, c, e, and g) and non-classical (b, d, f, h) monocytes were stained for CD163 (a, b), CD25 (c, d), CD206 (e, f), and IL-13Rα1 (g, h) expression. The data are presented as the percentage of total classical or non-classical monocytes for each group. *** = p < 0.001 are relative to the normal

Fig. 4

Increased CD163 and CD206 expression density in classical and non-classical monocytes in COPD patients. Classical (a, c, e) and non-classical (b, d, f) monocytes were stained for CD163 (a, b), CD206 (c, d), and CD25 (e, f) expression. The degree of expression is reported as the MFI

Fig. 5

Reduced numbers of CD206 + CCR5+ monocytes with increased inflammatory phenotype in severe COPD. CD206 + CCR5+ classical (a, c, e, g) and CD206 + CCR5+ non-classical (b, d, f, h) monocytes were also stained for CD14 (c, d), CD163 (e, f) and CCR5 (g, h) expression. The degree of expression is reported as the MFI

Fig. 6

Elevated expression of CCR5 in CD206 + CCR5+ monocytes in severe COPD. Panels a and b are representative histograms of CCR5 expression on CD206 + CCR5+ classical and non-classical monocytes shown in Fig. 5. Results are representative of the 11 COPD-S patients