Proliferating alveolar macrophages in BAL and lung function changes in interstitial lung disease

In interstitial lung disease, the number of alveolar macrophages (AMs) can be increased. This may be caused by recruitment of precursor cells from peripheral blood and/or local proliferation in the lung. We therefore analysed proliferation, by studying both the expression of the nuclear proliferation antigen, Ki67, and the deoxyribonucleic acid (DNA) content, using the Feulgen reaction followed by cytometry. The patients had interstitial lung disease, i.e. sarcoidosis (n = 20), extrinsic allergic alveolitis (n = 20), idiopathic lung fibrosis or lung involvement in collagen-vascular disease (n = 19). In all patient groups there was a significant increase in proliferating AMs compared to healthy controls (4.2 versus 1.4% Feulgen, 2.1 versus 0.5% Ki67), with a significant correlation between these two parameters. A positive correlation was also found in bronchoalveolar lavage (BAL) between numbers of lymphocytes and proliferating cells in sarcoidosis and in fibrosis. In fibrosis, numbers of eosinophils and proliferating cells were also positively correlated. Our main finding was, however, a positive correlation between numbers of proliferating cells (Feulgen) and lung function parameters, especially vital capacity and oxygen tension (PO2) at rest, in patients with sarcoidosis and lung fibrosis. By contrast, in extrinsic allergic alveolitis, no correlation could be observed between proliferating cells and cell population or lung function. Our results suggest that local proliferation of macrophages is an important element in interstitial lung disease.

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