The difference between staying well and suffering days of misery depends on which of two contradictory ways the immune system reacts to infection by the flu. One strong reaction releases inflammatory chemicals leading to sickness, researchers report online August 25 in PLoS Genetics. An equally strong but opposite reaction produces anti-inflammatory compounds and fights off the flu without producing symptoms.
Most of what researchers know about influenza’s effect on people comes from studies of people who are already sick. But Alfred Hero and his colleagues wanted to know how some people seem to be able to avoid getting sick. The researchers infected 17 volunteers with a strain of seasonal flu called H3N2/Wisconsin.
Nine of the volunteers got sick. Some of the others reported feeling under the weather, but had no clinically discernible symptoms. The researchers drew blood before the flu inoculation and every eight hours for five days after the initial infection. The team then examined the activity of about 22,000 genes in each blood sample.
“The persistent patterns that came out of this were striking to say the least,” says Hero, a computer scientist and electrical engineer at the University of Michigan Medical School.