[Pathogenetic aspects of sarcoidosis. Importance of local complement synthesis in alveolar macrophages]

Sarcoidosis is a multisystem granulomatous disorder of unknown etiology. Markers of activity include elevated serum ACE levels, interleukin 2-receptors, hypercalcemia, hypercalciuria, intrathoracic uptake of radioactive gallium, retinal vascular leakage, and an increased T4/T8 ratio in bronchoalveolar lavage fluid. The three main pathological features of sarcoidosis are alveolitis, granuloma formation and fibrosis. The cells harvested by bronchoalveolar lavage in sarcoidosis are representative of the local inflammatory reaction seen in the lung. Alveolar macrophages have the potential to synthesize the components of the functional alternative and terminal pathways of complement. The alveolar macrophages from sarcoidosis patients produce more complement than their healthy counterparts. Complement participates in the normal metabolism of immune complexes and has the ability to modulate immune responses via complement receptors present on virtually all cell types. On the other hand, through enhanced levels of complement factors, an increased number of activated macrophages in the lung may contribute to a changed immune response, which may be of significance for the granulomatous inflammation seen in sarcoidosis and may also contribute to the tissue damage seen in sarcoid fibrosis.