The researchers asked young adults to watch a 10-minute slide show containing a series of unpleasant photographs. Some of these participants looked at pictures of people who looked obviously sick in some way (people with pox and rashes, people coughing and sneezing and blowing mucus out of their noses).
The participants gave blood samples both before and after each slideshow. Next the researchers exposed these blood samples to a bacterial infection, and measured the extent to which white blood cells produced interleukin-6 (IL-6). IL-6 is a proinflammatory cytokine that white blood cells make when they detect microbial intruders. More IL-6 indicates a more aggressive immune response to infection. So, by measuring IL-6 before and after the slide show, the researchers were able to determine whether seeing pictures of disease-y people actually stimulated the immune system to fight infection more aggressively. And it did.