Catch Your Breath – with Alveolar Macrophages
While we’d all like to take a nice breath of fresh air, chances are you really aren’t. Worldwide, air pollution is a leading cause of death and disease. Now, large studies conducted in Europe and China have methodically established that exposure to air pollutants is also associated with an increased risk for diabetes.
Our lungs’ highway patrol
Surely our bodies have a defense mechanism against these risky pollutants, including particulate matter (PM), nitrogen dioxide and ozone, right? Yes! In the event that you inhale air pollution particles, our trusty alveolar macrophages (AMs) launch the body’s initial local immune response. If we think of the lungs as a highway, then the AMs are the highway patrol making sure there are no “obstacles” (or pathogens) disrupting the flow of things. The AMs can respond in two different ways:
- The M1 polarization response is pro-inflammatory, releasing associated cytokines (IL-12, IFN-γ).
- The M2 polarization response is anti-inflammatory, releasing associated cytokines (IL-4, IL-10 and IL-13).
But air pollutants don’t really abide by the “law of the lung.” Here’s why:
- Studies have found that when human AMs are exposed to a PM, high levels of pro-inflammatory cytokines (M1) and low levels of anti-inflammatory cytokines (M2) occur.
- However AM exposure to these air pollutants can throw off the lungs’ normal response, causing an abnormal one.
- This abnormal response is not limited to the lungs since a systemic inflammatory response can follow — which may include the pancreas.
What does this mean for T1D? Once the air pollution particles instigate a response from the AMs, this may cause a cascade of immune attacks in the rest of the body’s organs, including the pancreas, where the AMs release pro-inflammatory cytokines and cause an autoreactive reaction toward the beta cells, ultimately leading to T1D.
- Dahlén, E., Dawe, K., Ohlsson, L., & Hedlund, G. (1998). Dendritic cells and macrophages are the first and major producers of TNF-α in pancreatic islets in the nonobese diabetic mouse. The Journal of Immunology, 160(7), 3585-3593.
- Xing, Y. F., Xu, Y. H., Shi, M. H., & Lian, Y. X. (2016). The impact of PM2. 5 on the human respiratory system. Journal of thoracic disease, 8(1), E69.
- Xu, X., Jiang, S. Y., Wang, T. Y., Bai, Y., Zhong, M., Wang, A., … & Sun, Q. (2013). Inflammatory response to fine particulate air pollution exposure: neutrophil versus monocyte. PLoS One, 8(8), e71414.