Alveolar presence of red blood cells correlates with alveolar macrophage iron levels in COPD

ackground: Pulmonary iron levels are increased in COPD patients. The number of iron positive alveolar macrophages correlates with increased COPD severity, which may be due to iron deposition from cigarette smoke or from red blood cells. We hypothesized that COPD patients have increased numbers of red blood cells in the alveolar space leading to increased macrophage iron levels.

Methods: Lung sections from 7 non-smokers (NS), 19 smokers (S) and 27 COPD patients were analysed to measure the percentage of alveolar space covered by red blood cells (RBC). In a subset (n=27) alveolar macrophage iron levels were also quantified using Perls staining and the Golde iron staining intensity score.

Results: The percentage of alveolar space occupied by RBCs is increased in COPD compared to NS and S. GOLD stage III patients had a significant increase compared to NS and S (Table 1). A similar trend was observed for alveolar macrophage iron levels (Golde Score) with GOLD stage III patients showing increased iron (Table 1). The alveolar macrophage iron levels showed a significant positive correlation with the percentage of alveolar space occupied by RBCs (r=0.40, p=0.03).

Conclusions: COPD patients have increased alveolar RBC likely due to microhaemorrhage. Phagocytosis of RBCs by macrophages may increase iron levels, altering macrophage function.