Biomedical Engineering Reference
In-Depth Information
6
Macrophages
Peter J. Barnes
National Heart and Lung Institute, Imperial College School of Medicine,
London, U.K.
I.
INTRODUCTION
Alveolar macrophages play a critical role in innate and acquired immunity,
in the defense of the respiratory tract against pathogens, and in the clear-
ance of inhaled particles. They also play an important role in the inflamma-
tory response and there is increasing evidence that they play a pivotal role in
the pathophysiology of COPD. Because of the extraordinary diversity of
macrophage responses they can account for most of the known features
of COPD (1-5) (Fig. 1).
II.
INCREASED MACROPHAGE NUMBERS IN COPD
There is a marked increase in the numbers of macrophages in airways, lung
parenchyma, BAL fluid and sputum of smokers and patients with COPD. A
careful morphometric analysis of macrophage numbers in the parenchyma
of patients with emphysema showed a 25-fold increase in the numbers of
macrophages in the tissue and alveolar space compared with normal
smokers approximately matched for cigarette exposure (6). Furthermore,
macrophages are localized to sites of alveolar wall destruction in patients
with emphysema (7,8). Indeed, there is a correlation between macrophage
numbers in the airways and the severity of COPD (9).
Clusters of macrophages are also found around small airways and
associated with peribronchiolar fibrosis in respiratory bronchiolitis (RB)
(10). This is exclusively seen in smokers and ex-smokers and may persist
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