Differential Response of Human Nasal and Bronchial Epithelial Cells Upon Exposure to Size-Fractionated Dairy Dust

Abstract

Exposure to organic dusts is associated with increased respiratory morbidity and mortality in agricultural workers. Organic dusts in dairy farm environments are complex, polydisperse mixtures of toxic and immunogenic compounds. Previous toxicological studies focused primarily on exposures to the respirable size fraction; however, organic dusts in dairy farm environments are known to contain larger particles. Given the size distribution of dusts from dairy farm environments, the nasal and bronchial epithelia represent targets of agricultural dust exposures. In this study, well-differentiated normal human bronchial epithelial cells and human nasal epithelial cells were exposed to two different size fractions (PM₁₀ and PM_>10) of dairy parlor dust using a novel aerosol-to-cell exposure system. Levels of proinflammatory transcripts (interleukin [IL]-8, IL-6, and tumor necrosis factor [TNF]-α) were measured 2 h after exposure. Lactate dehydrogenase (LDH) release was also measured as an indicator of cytotoxicity. Cell exposure to dust was measured in each size fraction as a function of mass, endotoxin, and muramic acid levels. To our knowledge, this is the first study to evaluate the effects of distinct size fractions of agricultural dust on human airway epithelial cells. Our results suggest that both PM₁₀ and PM_>10 size fractions elicit a proinflammatory response in airway epithelial cells and that the entire inhalable size fraction needs to be considered when assessing potential risks from exposure to agricultural dusts. Further, data suggest that human bronchial cells respond differently to these dusts than human nasal cells, and therefore that the two cell types need to be considered separately in airway cell models of agricultural dust toxicity.

Additional information

Funding

The authors thank Robert Devlin and Lisa Dailey at the U.S. EPA for their donation of the NHBE cells used for this work. They also thank Margaret Davidson for her assistance with dust collection and cell culture. This work was supported by the High Plains Intermountain Center for Agricultural Health and Safety and grant U54OH008085 from the National Institute of Occupational Safety and Health. This work was also supported, in part, by a grant from the National Institute of Environmental Health Sciences (R01ES019325).