The effect of repeated exposure to particulate air pollution (PM10) on thebone marrow

Studies have shown that exposure to ambient particulate matter is related t o an increased cardiopulmonary morbidity and mortality. The present study w as designed to measure the effect of repeated exposure to urban air particl es (PM,,) on the rate of production and release of polymorphonuclear leukoc ytes (PMN) from the bone marrow into the peripheral blood. Rabbits exposed to PM,, (5 mg) twice a week for 3 wk, were given a bolus of 5'-bromo-2'-deo xyuridine (BrdU) to label dividing cells in the marrow that allows us to ca lculate the transit time of PMN in the bone marrow mitotic and postmitotic pools. The PM10 exposure (n = 8) causes a persistent increase in circulatin g band cells (p < 0.05) and a shortening of the transit time of PMN through the postmitotic pool in the marrow (64.4 +/- 2.2 h to 56.3 +/- 2.2 h, p < 0.05) if compared with vehicle-exposed control subjects (n = 6). PM,, expos ure increases the bone marrow pool of PMN particularly the mitotic pool of PMN (p < 0.05). The PM,, were distributed diffusely in the lung and caused a mild mononuclear inflammation. The percentage of alveolar macrophages con taining PM10 correlated significantly with the bone marrow PMN pool size (t otal pool r(2) = 0.56, p < 0.012, mitotic pool r(2) = 0.61, p < 0.007) and the transit time of PMN through the postmitotic pool (r(2) = -0.42, p < 0.0 43). We conclude that repeated exposure to PM10 stimulates the bone marrow to increase the production of PMN in the marrow and accelerate the release of more immature PMN into the circulation. The magnitude of these changes w as related to the amount of particles phagocytosed by alveolar macrophages.