A study from the University of British Columbia shows that people's immune systems are activated just by seeing other people with obvious signs of sickness, such as pox or coughing.

People's immune systems generally lie in a watchful state similar to standby. A constantly ramped up immune system would consume large amounts of energy, be temporarily debilitating and can cause its own brand of sickness — autoimmune diseases. But in the short term, it may be useful for a person's immune system to respond aggressively to information suggesting that there's a high risk of infection, such as the presence of nearby individuals who are sick.

A stronger immune response was seen in the blood of people who had watched the slides of sickness

In the study, 28 subjects were shown different slide shows on two different days. On the first day, all watched slides of furniture as a control. On the second day, half saw slides of guns being aimed at them and the other half saw a disease slide show: people with pox, blowing their nose, sneezing, etc. Blood samples were taken from the subjects both before and after they saw the slides. Bacteria were then added to the blood samples and the immune response measured. A stronger immune response was seen in the blood of people who had watched the slides of sickness. Immune response was measured by testing the level of the compound interleukin-6, a general indicator of immune system activity.

There are certainly times when it would be useful for people to temporarily boost their immune response. The study opens up the intriguing possibility that there may be several as yet unknown ways to do so. If merely looking at picture of sick individuals generates an immune response, what other actions might also do so? After all, people are able to alter their heart rate, though any elementary biology text will describe the heart as a muscle not subject to voluntary control. It has been known since the 1960s that heart rate can be partially controlled through changes in thinking, emotions or behavior. It's not beyond possibility that people may be able to exhibit some degree of control over their immune function, too.

It will take further studies to show if there are practical ways that the mind can be used to strengthen or dampen the activity of an individual's immune system.

An article detailing the study was published in the May 2010 issue of Psychological Science.