That is because roughly one tenth of a person’s circulating T cells are specific for cytomegalovirus. Yet although more than three of five adults have been infected with the microbe, most would not know it. Indeed, cytomegalovirus has learned to set up shop almost anywhere in the human body. “The fact that a virus is still around means it is really good at what it does.” “They have to get past physical and innate barriers-it is tough to succeed,” says Peter Barry, a biologist who studies cytomegalovirus at the University of California, Davis.

In order to survive, viruses must hijack a person’s host cells to churn out more viral particles. The Epstein–Barr virus, another microbe that frequently infects people, had no such effect.Ĭytomegalovirus’s profound influence on the immune system is, perhaps, not so shocking. Whereas the results don’t show whether these changes produce an overall stronger or weaker immune response, they do indicate “cytomegalovirus has a really profound effect,” Davis says. A single environmental factor-a past infection with common cytomegalovirus-affected 58 percent of the tested parameters. “We were surprised by the degree of environmental influence on so many components,” says Mark Davis of Stanford University School of Medicine, senior author on the new study. The findings, published January 15 in Cell, argue that life habits and experiences shape our body’s defenses more than the DNA passed down from our parents.Īlthough prior twin studies had hinted that nonheritable factors contribute to some autoimmune disorders, such as multiple sclerosis, the recent analysis was one of the first to quantify genetic and environmental effects on the general immune system. And among identical twin siblings, who have the same genome, immune system features differed more strikingly within older twin pairs than in younger sets. Genetics had almost no effect on how well individuals responded to the flu vaccine, judged by antibodies produced against the injected material. Differences in three fourths of these parameters depended less on genetics than on environmental factors, such as diet and prior infections. They measured immune cell populations and their chemical messengers-204 parameters in all-before and after participants received a flu shot. In one of the most comprehensive analyses of immune function performed to date, researchers analyzed blood samples from 105 sets of healthy twins. A new study of twins, however, suggests otherwise. Some people seem better than others at fighting the flu, and you might suspect they were born that way.

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