Effects of elevated CO₂ levels on lung immune response to organic dust and lipopolysaccharide

Workplaces with elevated organic dust levels such as animal feed barns also commonly have elevated levels of gasses, such as CO₂. Workers exposed to such complex environments often experience respiratory effects that may be due to a combination of respirable factors. We examined the effects of CO₂ on lung innate immune responses in mice co-exposed to the inflammatory agents lipopolysaccharide (LPS) and organic dust. We evaluated CO₂ levels at the building recommended limit (1000 ppm) as well as the exposure limit (5000 ppm). Mice were nasally instilled with dust extracts or LPS and immediately put into chambers with a constant flow of room air (avg. 430 ppm CO₂), 1000 ppm, or 5000 ppm CO₂ enriched air. Results reveal that organic dust exposures tended to show decreased inflammatory responses with 1000 ppm CO₂ and increased responses at 5000 ppm CO₂. Conversely, LPS with addition of CO₂ as low as 1000 ppm tended to inhibit several inflammatory markers. In most cases saline treated animals showed few changes with CO₂ exposure, though some changes in mRNA levels were present. This shows that CO₂ as low as 1000 ppm CO₂ was capable of altering innate immune responses to both LPS and organic dust extracts, but each response was altered in a different fashion.