Reading Research: Psychological Stress and the Immune System

Even though I’ve been reading plenty about stress in a couple of books (see The Stress of Life, Status Syndrome, and Why Zebras don’t get Ulcers), I’ve also managed to find the time to read a few interesting studies.

Since I don’t have any obvious places to write about them (my main stress posts cover the basic principles rather than more recent findings (see my posts on what is stress? how does stress work? and how does stress make us ill?), I decided to start a reading research series.

I looked at a meta-analysis about chronic stress and the HPA axis last week.  This week, I’m going to have a look at another meta-analysis.  This one is about stress and its effect(s) on the human immune function.

The article is Psychological Stress and the Human Immune System: A Meta-Analytic Study of 30 Years of Inquiry, by Suzanne Segerstrom and Gregory Miller, Psychological Bulletin, 2004

Here’s a quick summary plus a few thoughts.

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OK, what’s it all about?

Well, as I noted in my post yesterday about stress and disease, the authors note that as at 2004, there had been over 300 studies done over a 30 year period that demonstrated that stress causes an immune response in humans (i.e. not counting animal studies).

The authors performed a meta-analysis and divided their results into the following classification of stressors:

1. Acute, time-limited stressors – basic lab-based challenges like mental arithmetic
2. Brief, naturalistic stressors – real-life challenges like meaningful exams or driving tests
3. Stressful event sequences – a series of events that occur in relation to one another, such as moving house and managing childcare following a messy divorce
4. Chronic stressors - a fundamental change to a person’s identity or life, including disability, serious illness or repatriation
5. Distant stressors – traumatic experiences from a long time ago

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The findings

The meta-analysis made the following findings:

Acute, time-limited stressors

These stressors showed increases in immune response in natural immunity but not in specific immunity.  This makes sense, because the specific immune system takes ages to get going anyway so wouldn’t be of use in an emergency.

If you missed yesterday’s post, or don’t remember, human immunity divides into two basic classifications, natural and specific.

Natural responses are those that pretty much all organisms have, including basic organisms like sponges.  They respond fairly quickly to pathogens entering the body.

Specific responses are more dependent on the type of creature involved and take longer to respond to enemy agents.

Brief, naturalistic stressors

These stressors did not show the changes shown by acute, time-limited stressors. However, they did show a shift away from cellular immunity and towards humoral immunity, which explains why people always go down with a cold virus close to their examinations.

If you missed yesterday’s post, or don’t remember, human specific immunity comprises cellular and humoral responses, as follows:

Cellular responses are those made against invaders that try to get inside our cells (like viruses).  Cellular responses are co-ordinated by a subset of T-helper cells called Th1 cells, which produce cytokines including IL-2 and IFNγ.

Humoral responses are made against larger invaders like parasites and bacteria.  Humoral responses are co-ordinated by a subset of T-helper cells called Th2 cells, which produce different cytokines, including IL-4 and IL-10, which activate B cells and other natural response cells, including mast cells.

Stressful event sequences

The meta-analysis was not able to find reliable trends in the data for stressful event sequences, possibly because of the unreliable nature of the events.

Chronic stressors

Chronic stressors, which are ongoing over a long period of time, were implicated in severe and complete reduction in functioning of the immune system across the natural and specific systems.

Distant stressors

The meta-analysis was not able to find reliable trends in the data for distant stressors because of a paucity of data.

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So what?

Well, what is interesting is that this meta-analysis has concluded that it is not correct to say that stress always causes a reduction in immunity.  Stress changes immunity and more specifically, it:

• Reduces specific immune response in circumstances of fight-or-flight, in favour of the faster-acting natural response
• Alters specific immune response to emphasise attacks on parasites and bacteria instead of viruses in circumstances of brief, naturalistic stressors (which may or may not be status related?)
• Reduces the whole immune response under circumstances of chronic stress

Things are never as simple as we want them to be.