[RU 41740: mode of action on the respiratory system]

Alveolar macrophages are issued from circulating monocytes and stand at the cross-road of all antixenic defences of the lung. They are obtainable for in vitro studies by alveolar lavage, and their properties have been determined during the last few years. Synthesis activity and secretion of inflammation mediators, enzymes, enzyme inhibitors, free radicals and factors of cell co-operation are responsible for the defence of the lungs. The phagocytic activities of alveolar macrophages and their ability to promote cell co-operation make them cells that are capable of antigenic presentation, a fundamental step in the development of immunological defence mechanisms. The effectiveness of RU 41740 in respiratory infections is due to its action on deep lung cells, and in particular alveolar macrophages. This compound has been shown to recruit cells (which is a sign of macrophage activation), to increase enzymatic activities, phagocytosis and release of free radicals and to promote interleukine 1 secretion. These activities have been demonstrated in in vitro studies as well as in animal and human studies.