© 2002 British Occupational Hygiene Society Published by Oxford University Press DOI: 10.1093/annhyg/mef607 Effect of Crystalline Silica Particles on PMN Release

Previous studies have shown that immature polymorphonuclear leukocytes (PMNs) newly released from the bone marrow on pulmonary inflammation may preferentially sequester in the lung and cause endothelial damage in the lung microvessels, which may contribute to the observed decrease in lung function. The aim of this study was to determine changes in PMN release from the bone marrow induced by crystalline silica. Japanese white rabbits were exposed to crystalline silica (Min-U silica, 50 mg) (n = 6) intratracheally. The systemic inflammatory response was measured as changes in circulating 5′-bromo-2-deoxyuridine (BrdU)-positive PMN (PMNBrdU) newly released from the bone marrow. Silica exposure caused a shortening transit time of PMN through the bone marrow, especially in their last division in the mitotic pool, than in the control (P < 0.02). A BAL study 48 h after instillation of crystalline silica showed that the number of PMN and PMNBrdU recovered by lavage was significantly greater than from the control (P < 0.05). We conclude that, as with other inflammatory sources such as cigarette smoking, ambient particulate matter or pneumococcal pneumonia, crystalline silica instillation into the lung induces immature PMN from bone marrow and may contribute to the observed pulmonary lesion