Macrophage reaction in rabbit lung following inhalation of iron chloride

Groups of eight rabbits were inhalation-exposed to iron, 1.4 +/- 0.7 mg/m3 (low Fe), or 3.1 +/- 1.8 mg/m3 (high Fe) as FeCl3 or to filtered air (controls) for 2 months, 5 days/week and 6 hours/day. The alveolar macrophages were increased in number in both exposed groups. Noduli of granular macrophages were found in lungs of all the rabbits in the high-Fe group, in one from the low-Fe group, and in one control rabbit. Especially in the high-Fe group there were prominent changes in the macrophages such as enlarged lysosomes containing fibrous-looking structures, iron-rich inclusions, and densely packed, 5-nm electron-dense granules. The number of cells filled with surfactant-like inclusions as well as a smooth surface was increased in the high-Fe group and the macrophages had enhanced phagocytic capacity. There was an increase in the phospholipid concentration and in the volume density of type II cells in the high-Fe group but the level of phosphatidylcholines was not significantly changed. The fact that Fe3+ affected mainly the alveolar macrophages might be due to the relatively high concentration of iron in these cells caused by the precipitation of iron in their lysosomes.