Can Our Immune Systems Tell Us Who's Sick?

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The placebo effect relies on the mind's ability to influence the body, but does the same work in reverse? For instance, after being sick, can the body's immune system subconsciously tell us who's sick so we can avoid getting sick again?

In one early analysis on the topic, researchers think it's certainly possible. The research, featured in the journal Psychological Science, suggests people who recently felt ill are primed to notice and avoid others who appear sick around them. In this sense, their biological immune systems and behavioral immune systems work together in some way to help avoid future illness.

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Though the exact way biology influences behavior in this context is unclear, scientists guess a gap of vulnerability in the body's biological immune system plays a role. When the immune system launches an attack on a microbe invader — let's say the common cold virus, it releases of a type of protein called cytokine interleukin-10 that causes inflammation and helps the body overcome the bug. Yet to avoid keeping the body in a heightened immune stage unnecessarily, the system sends another type of cytokine with anti-inflammatory properties. With its guard down while recovering from the previous sickness, the body is most vulnerable to other pathogens at this time.

Enter the behavioral immune system, researchers say, which may bridge this gap by helping people spot and avoid others who are sick.

To test the hypothesis, researchers conducted two experiments looking at whether recently sick people paid more attention to others who are sick and if they subconsciously avoided others who may feel under the weather. Before each experiment, researchers asked participants questions to ensure people with stronger reactions to getting sick (the germaphobes, if you will) were noted in the sample. People were also grouped into "recently sick" and "not recently sick" based on their responses to certain questions.

In the first set-up, 96 undergrads between the ages of 18 and 30 were placed in front of a module that quickly flashed series of faces in front of them. Some faces showed disfigured expressions, which other research suggests brings about an innate aversion in humans, perhaps because it can signify infectious disease. This could be something as simple as a photo of another person sneezing. Researchers found participants who were recently sick focused longer on the disfigured faces, meaning they subconsciously paid attention to them longer than the other group that wasn't recently sick.

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The second experiment — with 117 different participants between the ages of 18 and 35 — had a similar set-up, but this time people in each group were asked to quickly judge whether they would approach a person based on seeing their faces flash on a screen. This time, recently sick participants responded faster than the other group in reporting who they would avoid (which primarily included the disfigured faces).

Of course, there's only so much one can draw from these indirect studies, which is why the scientists call for other experiments to address issues with the research, including relying on participants' reports of being sick rather than measuring them firsthand.

The findings may explain some people's less than social attitude after catching that first common cold this year.

Photo by mcfarlandmo/Flickr.com

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