Let’s take ozone for example. Ozone is cheekily described as “good up high, bad nearby”. In other words, ozone in the atmosphere is a good thing because it filters dangerous solar UV radiation, but ozone at ground-level is unfavorable because it is toxic to the body, causing coughing, respiratory inflammation, chest pain, etc, and can contribute to health issues such as asthma and cardiovascular disease.
What I find to be particularly interesting are studies like Devlin et al. (1997) that provide insight into the variety and complexity of the body’s responses to specific pollutants.
First, a little background information. When a toxic substance enters the body our immune system responds with a myriad of cellular and molecular changes (represented by the presence of “markers”) that are meant to neutralize or minimize the threat posed by the substance. These changes can be measured, and thus a substance can be identified as dangerous to the body because it elicits certain biological responses.
Inflammation is one example of an immune system response to a potential threat. Many studies use measurements of cell markers of inflammation in fluid inside the lungs to find out if a substance is toxic. However, inflammation markers are not the only measure of how much of a threat something poses to our bodies. For example, Devlin et al. also measured a marker called lactate dehydrogenase, an enzyme released when cell are injured or die.
Interestingly, some markers (eg. inflammation markers) stopped appearing after extended ozone exposure, in other words their response was attenuated. This suggests that the body stops responding negatively to ozone. So the question remained, “IS OZONE BAD FOR US?”.
But, other markers, namely lactate dehydrogenase did not attenuate, and was found to be present throughout elongated and repeated exposures to ozone. This suggests that ozone does continue to damage the body.
I am no cellular or molecular biologist, so bare with me. But, from what I gather, these variations in response at the cellular and molecular level hint at the complexity of the immune system. Now I am sure others have a better explanation, but for my own sake I would like to offer one possible explanation for the observed differences in inflammation and lactate dehydrogenase response and say that it is partly a function of limited resources and demand. This isn’t supposed to be economics, so let me explain.
The fact that inflammation markers are found to attenuate after repeated exposures suggests to me that the immune system is capable of re-allocating those resources in the face of inescapable adversity. Put another way, the immune system is often talked about as a sense organ and can make “decisions” based on the sensory input. In this example, the immune system detects a threat to the body (ozone) and the body initiates it’s first line immune response, inflammation. Since the exposure to ozone did not abate, and inflammation is an entirely ineffective response to ozone (granted inflammation is great at neutralizing an infection, but inflammation doesn’t do much to stop or protect us from ozone), the immune system “knew” to withdraw/attenuate the inflammation response. In this way the immune system does not employ brut force methods to dealing with toxins, but has the ability to try a certain approach and sensing whether or not it is working, and if not, then it stops using that approach. Very cool!
Not so cool was that the researchers found that the participants cells continued to release lactate dehydrogenase, indicating that the cells were still injured during both acute and long-term exposure to ozone. What this suggests then is that while ozone may not pose a long-term threat to our health via extended periods of inflammation (which can lead to disease such as asthma and cancer), one way or another ozone does continue to injure the cells that make up the lining in our lungs. Thus, ozone needs to be avoided and the levels of it in our environments should be reduced.
I think this sort of research is interesting but also very important for human health in general. We need to continue to investigate how various chemical compounds impact our bodies. A great area of uncertainty stems from the rise of nano technology and molecular manufacturing. There are many unanswered questions about whether or not these synthetic materials that are built on a molecular level will pose health threats, particularly to our respiratory system and immune system. I bet we will see a surge of research in these areas in the coming years.