Exposure to the dust in pig barns has been shown to affect short-term measures of inflammation and immune function in swine workers. Models of such exposure that used human or mouse lung immune cells (alveolar macrophages, AM) showed negative effects on both maturation and function of these important cells. Because these effects could be detrimental to swine health, we want to know whether pigs are similarly affected by such dust, or if they have become tolerant to it. As a first step, our objectives in this project were to test whether extracts of swine barn dust (termed organic dust extract, ODE) have the same effects on swine macrophages in culture as seen for human macrophages.
We collected AM from eight healthy pigs, exposed these cells in culture to different amounts of ODE, and found that exposure to ODE activated the swine macrophages to express inflammation signaling proteins, as well as other proteins known to be part of a normal immune response process. Interestingly, one of the proteins is the co-receptor for PRRSV. As AM are the primary cell infected by PRRSV, exposure to dust could potentially be increasing the vulnerability of these lung macrophages to PRRSV infection. Further, ODE exposure decreased important immune function of these cells, including their normal ability to uptake particles in the environment and to kill intracellular bacteria, as has been seen in human cells similarly exposed to ODE. We also found that the ODE-treated pig cells could not fully activate a critical regulator of inflammatory pathways in response to a separate inflammatory signal (endotoxin), providing a mechanism for some of these negative effects. We interpret the results of this in vitro model to indicate that swine macrophages can be affected by exposure to dust, and that experiments to test whether pigs themselves are negatively affected by such exposure is warranted. If we can demonstrate in a follow-up study that growth or resistance to stress or disease is negatively affected, this would be important information to the industry as it evaluates the utility of dust mitigation. Further, the possible negative impact of dust exposure on PRRSv resistance should be specifically investigated.
