Sputum neutrophils are elevated in smelter workers, and systemic neutrophils are associated with rapid decline in FEV1

Objectives

In a previous study on smelter workers we, found significant relationship between exposure to dust and accelerated annual decline in forced expiratory volume in 1 s (FEV₁). In this cross-sectional study at the end of a follow-up, we aimed to investigate the possible association between annual decline in FEV₁ and markers of airways, and systemic inflammation in smelter workers.

Methods

Employees (n=76 (27 current smokers)) who had been part of a longitudinal study (9–13 years) that included spirometry (>6 measurements) and respiratory questionnaires, performed induced sputum, exhaled NO and had blood drawn. Participants with annual decline in FEV₁≥45 mL were compared with participants with annual decline <45 mL; also 26 non-exposed controls were included.

Results

Compared with non-exposed controls, smelter workers demonstrated a significantly increased percentage of neutrophils (mean (SD)) (57% (17) vs 31% (15)) and matrix metalloproteinases 8 (MMP-8) levels in sputum, and MMP-9, surfactant protein D (SpD) and transforming growth factor β (TGFb) levels in blood. A significant association in FEV₁≥45 mL was found for blood neutrophils when controlling for smoking habits (OR=1.7 (95% CI 1.0 to 2.8), p=0.045). Airway and blood protein markers were not associated with annual decline in FEV₁.

Conclusions

All workers displayed airway and systemic inflammation characterised by increased levels of neutrophils and MMP-8 in sputum, and MMP-9, SpD and TGFβ in blood compared with non-exposed controls. Blood neutrophils in particular were significantly elevated in those workers with the most rapid decline in lung function. A similar observation was not seen with airway neutrophils. In the present study, we were able to identify systemic but not airway inflammatory markers that can predict increased decline in FEV₁ in smelter workers.

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