Great immune system? Don’t thank your genes—they have little to do with it

Even Santa can get sick.
Even Santa can get sick.
Image: AP/Bela Szandelszky
We may earn a commission from links on this page.

Why do some people seem under the weather all the time, while others can share a bowl of chicken soup with a flu patient without getting the least bit sick?

It all comes down to the immune system. The strength of this hardware inside us to fight off disease varies considerably from person to person, and is affected by a number of factors, like age and nutrition. So it seems reasonable to think that genetics play a role, too. But how much of one?

Stanford researchers tackled that question in a study published Jan. 15 in the journal Cell. They took various immune system measurements in 105 sets of healthy twins, to separate genetic from non-genetic factors. They found that that while heritable factors do influence the immune system somewhat, non-heritable factors are more important.

This was not the finding the researchers expected. Mark Davis, senior author of the study, told Scientific American that his team was “surprised by the degree of environmental influence on so many components.”

One of the biggest factors was whether or not subjects had been infected with a specific virus in the herpes family. Known as “cytomegalovirus,” it is very common—between 50 and 80% of US adults have had it, though most are unaffected by it—and it had a huge impact on the subjects’ immune systems.

Whether that impact is positive or negative, though, is difficult to tease out. From Scientific American’s report:

Ultimately, it is going to depend on the individual, notes Chris Benedict, an immunologist at the La Jolla Institute for Allergy and Immunology in California. Infectious diseases and autoimmune disorders are two of our biggest killers. “It’s always a balancing act,” Benedict adds. “The immune system has to respond well to infections but not so robustly that it causes autoimmunity.”