Cytokine levels in crystalline silica exposed rock drillers

Abstract

Background: Inhaled crystalline silica may cause lung function decline. However, biological mechanisms associated with pulmonary effects in exposed workers have not been completely elucidated. Objectives: We aimed to investigate if crystalline silica exposed rock drillers had induced systemic inflammation compared to a group of referents. Methods: Serum samples were collected in 121 male rock drillers and 48 male referents after examination with spirometry in a cross-sectional study. Air samples were collected in a sub-sample of the drillers. Cumulative exposure to crystalline silica was calculated based on the measured air concentration of α-quartz and their occupational history. The interleukins IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-13, TNF and IFN(interferon)γ were measured. Results: Geometric mean current and cumulative exposure to crystalline silica were 36 µg/m3 and 234 µg/m3, respectively. The rock drillers had been exposed for 10.4 years on average. None of the cytokine concentrations differed significantly between the groups, but multiple linear regression analysis showed that IL-6 and IL-8 were negatively associated with being exposed. When stratifying the non-smoking exposed subjects into three equally large groups according to cumulative exposure, the highest exposed subjects had significantly lower concentrations of IL-12 and IL-6. IL-12 was also significantly associated with FEV1/FVC, suggesting lower concentrations by lower ratio. Conclusions: Surprisingly, there was a tendency towards lower pro-inflammatory cytokine concentrations in exposed workers. Whether these observations may be related to polarization towards M2 pulmonary macrophages remains to be elucidated.