Alveolar macrophage size is increased in COPD patients compared to controls

Background: Lung macrophage numbers are increased in COPD. Subpopulations of pulmonary macrophages have been identified based on anatomical location and/ or size and granularity. These subpopulations display differences in phenotype and function. We investigated differences in lung macrophage size in the alveolar compared to interstitial regions, and compared COPD patients to controls. Methods: Lung tissue blocks were obtained from 13 non-smokers (NS), 17 smokers (S) and 9 COPD patients (COPD) undergoing lung resection for treatment of lung carcinoma. Sections were cut and dual labelled for immunofluorescence with CX3CR1 and CD14. Dual labelled cells located in the alveolar spaces were defined as alveolar macrophages (AM) and those located in the alveolar walls or peripheral tissue were defined as interstitial macrophages (IM). Macrophage diameter was measured. Results: The median diameter of AMs was significantly greater in both COPD patients and S compared to NS (Table 1) (p<0.001 for both comparisons). The median diameter of the AM population was significantly larger than IM population for NS, S and COPD patients (Table 1) (p<0.001 for all comparisons). Table 1 NS S COPD P value IM diameter 13.2 (4.6-15.8) 11.5 (8.7-15.8) 11.7 (7.6-16.9) 0.0035 AM diameter 17.1 (2.9-27.4) 23.7 (14.1-25.6) 23.6 (13.4-25.7) <0.0001 P value <0.0001 <0.0001 <0.0001 Data show median (range) macrophage diameter (μm) Conclusion: Smoking increases the size of alveolar, but not interstitial, macrophages; this may be associated with functional changes. Alveolar and interstitial macrophages are phenotypically different based on size.