Phagocytosis of particulate air pollutants by human alveolar macrophages stimulates the bone marrow

Epidemiologic studies have shown an association between the level of ambien t particulate matter, 10 mm (PM10) and cardiopulmonary mortality. We have s hown that exposure of rabbits to PM10 stimulates the bone marrow. In this s tudy, we determined whether human alveolar macrophages (AMs) that phagocyto se atmospheric PM10 produce mediators capable of stimulating the bone marro w. AMs incubated with PM10 for 24 h produced tumor necrosis factor-alpha in a dose-dependent manner (86.8 +/- 53.29 pg/ml with medium alone; 1,087.2 /- 257.3 pg/ml with 0.1 mg/ml of PM10; P < 0.02). Instillation of the super natants from AMs incubated with 0.1 mg/ml of PM10 into the lungs of rabbits (n = 6) increased circulating polymorphonuclear leukocyte (PMN) and band c ell counts as well as shortened the PMN transit time through the bone marro w (87.9 +/- 3.3 h) compared with unstimulated human AMs (104.9 +/- 2.4 h; P < 0.01; n = 5 rabbits). The supernatants from rabbit AMs incubated with 0. 1 mg/ml of PM10 (n = 4 rabbits) caused a similar shortening in the PMN tran sit time through the bone marrow (91.5 +/- 1.6 h) compared with human AMs. We conclude that mediators released from AMs after phagocytosis of PM10 ind uce a systemic inflammatory response that includes stimulation of the bone marrow.