The lower respiratory tract of cigarette smokers contains an increased amount of iron that is predominantly sequestered within alveolar macrophages (AM), but is also present in alveolar epithelial fluid. Extracellular ferritin-bound iron could potentially be released by reductants present in cigarette smoke and catalyze generation of highly reactive hydroxyl radicals capable of causing oxidant injury. To determine whether AM are a source of alveolar extracellular ferritin and iron, we assessed in vitro release of iron, ferritin, and transferrin by AM recovered by bronchoalveolar lavage (BAL) of 27 healthy subjects including nine nonsmokers (NS), nine light smokers (LS), and nine heavy smokers (HS). Release of iron in vitro over 20 h was increased in AM recovered from LS (2.24 +/- 0.21 nmol/10(6) AM/20 h, p < 0.001) and HS (3.11 +/- 0.32 nmol/10(6) AM, p < 0.001) compared with NS (1.28 +/- 0.08 nmol/10(6) AM). Release of ferritin in vitro over 20 h was also increased in AM recovered from LS (71 +/- 24 ng/10(6) AM, p < 0.05) and HS (176 +/- 35 ng/10(6), p < 0.001) compared with NS (18 +/- 3 ng/10(6) AM). AM recovered from 12 smokers (8 HS, 4 LS) contained greater than 10 nmol of iron per 10(6) cells. These iron-loaded AM released a greater percentage of cell ferritin stores in vitro over 4 h (8.4% +/- 1.1, p < 0.01) than did AM from NS (3.2% +/- 0.6). Release of lactate dehydrogenase (LDH) over 4 h was substantially less (2.9% +/- 0.3, p < 0.001) than ferritin release.(ABSTRACT TRUNCATED AT 250 WORDS)