GSF scientists examine the role of small sputum macrophages in the widespread disease chronic obstructive bronchitis

COPD (chronic obstructive pulmonary disease) is one of the most common fatal diseases worldwide. In Germany alone, there are about 3-5 million patients affected. COPD includes both chronic obstructive bronchitis and emphysema. Both represent irreversible changes of the central and lower respiratory tract which are accompanied by coughing, mucus production and difficulty in breathing.

The increased production of mucus is induced by the immigration of neutrophilic granulocytes and macrophages. This can be further accompanied by the destruction of the bronchial epithelium and the alveolar septae and thus lead to emphysema. The disease progresses in episodic bursts; although it cannot be cured, early diagnosis and appropriate therapy allow it to bring the symptoms under control.

Macrophages play a central role in the air passages and the lung periphery (the alveoli). Macrophages originate in the bone marrow. Before entering the blood stream, these cells differentiate through precursor myelomonocytes to monocytes which migrate into the tissues and are then called macrophages. One of the major tasks of macrophages is to take up foreign particles, like bacteria, viruses, and aerosol particles, by phagocytosis.

Light microscope investigations of the leucocyte populations in induced sputum showed that in COPD patients up to 84% of the cells are neutrophils with macrophages comprising only 15%, whereas in healthy people macrophages form the majority (60%) of the leucocytes and only 36%, are neutrophils. The GSF clinical cooperation group “Inflammatory Lung Diseases” led by Marion Frankenberger has now succeeded in identifying a discrete new population of macrophages, smaller than the macrophages seen previously, among the cells in induced sputum from COPD patients.

The scientists have named this population “small sputum macrophages”. In healthy controls, this population constitutes only a small proportion, around 7%, of all macrophages, whereas in COPD patients it can rise to 90% of all macrophages during an acute episode. The first results indicate that the small sputum macrophages can contribute to the differential diagnosis of COPD and asthma, since they are only slightly increased in asthma patients compared to controls.

The inflammatory process in COPD remains poorly understood. It is possible that the small sputum macrophages play a central role in the pathogenesis of COPD. These cells exhibit characteristics of strongly activated inflammatory cells and might therefore play a crucial role in the inflammation of the respiratory tract in COPD.