Candidate innate immunity genes and cross shift pulmonary function changes among Western US dairy workers

Abstract

Objectives: Organic dust inhalation has been associated with adverse respiratory responses among dairy workers. Worker susceptibility may be driven by dust constituents, e.g. Gramnegative bacteria (endotoxin), Gram-positive bacteria (muramic acid); intrinsic factors, e.g. genetic traits, immune system; and extrinsic factors, e.g. smoking and work-related behaviors. The goal of this study was to characterize genetic markers related to lung disease and the endotoxin pathway by testing associations with cross-shift changes in forced expiratory volume in 1 second (FEV1) and candidate innate immunity genes. Methods: This study quantified breathing-zone personal work-shift exposures and pulmonary function among dairy workers during a variety of tasks. Inhalable dust was collected with Button samplers and analyzed for endotoxin (rFCassay). Pulmonary function tests (PFT) before and after the work shift included: forced vital capacity (FVC), FEV1 and the FEV1/FVC ratio. The maximum of three valid maneuvers was used in analyses. Venous blood samples were collected using Qiagen PAXgene tubes. Following DNA isolation (Puregene), candidate gene single nucleotide polymorphisms (SNPs) were analyzed using a custom genotyping array (Illumina GoldenGate assay on VeraCode technology). The assay was designed to include tagging SNPs for candidate genes in Hispanic populations. Genotyping data were cleaned and exported for analysis using the Illumina BeadStudio. Additive genetic modeling approaches were used to describe the distribution of SNPs and their relation to FEV1 cross-shift changes. Based on the frequency of haplotypes, genes were categorized as major (dominant) homozygous (AA), minor homozygous (bb), or heterozygous (Ab). Results: Eighty-eight participants (91% Hispanic, 88% male) had PFT and genetic results. Geometric mean levels of endotoxin were 469 EU/m3. On average, FEV1 was significantly reduced across the work shift among all dairy workers (-1.6%, 95% CI: -2.5, -0.7). No clear patterns were observed in FEV1 reductions by exposure tertiles. Differences in cross-shift reductions of FEV1 were observed across SNPs of the TLR4 (rs11536878, rs10759930 and rs1927911), TLR2 (rs3804099) and LY96 (rs7838114 and rs16938761) genes. Grouping heterozygous and minor homozygous SNPs (i.e., recessive model) may result in observable trends for CD14 SNPs. Conclusions: This is the first study characterizing candidate gene SNPs associated with the endotoxin pathway among Hispanic dairy workers. Associations with FEV1 changes were observed with SNPs for TLR4, TLR2 and LY96. The direction of the effect was not always consistent with previous literature on other populations, including northern Europeans and children. Next steps include multifactor analysis of relationships among genetic SNPs, exposure and cross-shift FEV1