Stress and Immune Function: Study with Video Lessons, Practice Problems & Examples

The immune system, crucial for defending against pathogens, relies on lymphocytes, a type of white blood cell. Chronic stress activates the HPA axis, leading to elevated cortisol levels that suppress lymphocyte production, diminishing immune function. This prolonged stress response increases susceptibility to illnesses, such as colds, as demonstrated in a study showing a linear rise in cold risk with extended exposure to stress. Understanding the relationship between stress and immune function is vital for maintaining health and preventing illness.

Stress and Immune Function

This video, we're going to be getting into in a bit more detail how stress can impact immune function because we have mentioned that a couple of times now. So I'm sure we all know what the immune system is, but just so that we're all on the same page, the immune system is essentially a very complex body system that protects against things like invading bacteria, viruses, and pathogens. And a really important player in the immune system are lymphocytes, which are a type of white blood cell that help your body to fight infection. And there are different types of lymphocytes. We have T cells, B cells, and natural killer cells.

You don't have to know any of those in detail. Just be aware that there are different types of lymphocytes. So what we essentially see is that activation of the HPA axis, particularly having cortisol in the bloodstream, suppresses lymphocyte production. And you don't have to know, like, all the physiology going on here, but just be aware that essentially when we're having this prolonged stress response and all this cortisol in the bloodstream, that is signaling to the body that we have to suppress nonessential functions, things like producing lymphocytes. So your body is operating under the idea that we are under this constant stress, this constant threat, so it doesn't want to be allocating energy to nonessential things.

So that's kind of what is going on here. And as I'm sure you can imagine, when we have fewer lymphocytes, the immune system is just kind of suppressed. It just can't do its job. It doesn't have the cells and the resources to be protecting us against invading bacteria and viruses the way it should be. And, again, you can imagine how this might not be a huge deal in the short term, but if we're experiencing stress happening over weeks or months or years, it's going to have a really powerful impact on our body over time.

And this was nicely demonstrated in a study by Cohen and colleagues back in 1998 where they were able to show that exposure to chronic stress did make people in their sample more susceptible to colds. So here, we have a graph adapted from their data. So we're looking over here at relative risk of a cold on the x-axis, and over here we're looking at if they were exposed to no chronic stressors versus chronic stress by durations. We have people who were exposed to less than one month, one to six months of chronic stress, six to twelve months, and then even greater than twelve months, so more than two years of chronic stress. So you can see how for people who had exposure to no chronic stressors, they had a relatively low risk of a cold.

I mean, no one's ever really at zero. Right? Cold germs are everywhere all the time, but relatively low risk. And then, we can see this really clear kind of linear increase in the relative risk of a cold based on how long people had been experiencing chronic stress with people who had been experiencing it for more than two years at the highest relative risk of a cold in this particular sample. So that's just a nice demonstration of how this can operate in the real world.

Alright, so that is stress and the immune system, and I will see you guys in the next one. Bye bye.

Example 1

Okay. So which part of the immune system is suppressed by the activation of the HPA axis? From what we know now, it seems like lymphocyte production is very suppressed when we have prolonged activation of the HPA axis. Specifically, it seems like the presence of cortisol in the bloodstream for very prolonged periods of time leads to suppressed development of new lymphocytes. So, we just kind of have fewer lymphocytes in our bloodstream and there is a decreased ability to fight off invading bacteria or viruses.

Now, both macrophages and granulocytes are types of white blood cells, but we have not seen the same consistent relationship found in research where if we have activation of the HPA axis we do not necessarily see consistent patterns of suppression of those two types of cells. And then nephrons are not part of your immune system. They are parts of your kidney. So those are just kind of irrelevant here. Alright.

So our answer is D, lymphocytes.