My answer to Is everyone naturally immune to some disease?

Answer by Connie b. Dellobuono:

Environmental influences have greater impact to our immune system than our genes.

The researchers also looked for genetic influence in the twins’ responses to flu vaccines. Some people react more strongly to vaccines than others, producing more antibodies: proteins that our bodies manufacture to identify and protect us from invading microbes. If this trait were genetic, identical twins would have similar responses. Instead, the variation in responses was almost entirely the result of environmental differences—presumably, what strains of flu the twins had previously been exposed to.

The researchers also studied the immune system impact of cytomegalovirus, which lies dormant in a large fraction of the population, rarely causing symptoms. Pairs of identical twins with different infection statuses—one was infected and the other was not—had more divergent immune systems than sets of twins in which both were uninfected. In fact, cytomegalovirus infection influenced nearly 60% of the parameters the scientists measured. “That’s kind of a smoking gun” that the variation is environmental, Davis says.

The work goes beyond previous research in its scope, says immunologist Jean-Laurent Casanova of Rockefeller University in New York City, who was not involved with the research. “To do a twin study and measure a tremendous number of immunological parameters, that is very novel.”

“There’s nothing here that is revolutionary or requires rethinking of our assumptions about how the immune system functions,” says David Baltimore, a biologist at the California Institute of Technology in Pasadena. But, he says, “I found it very impressive … that as we age, our immune systems become molded in increasingly individual ways.”

Environment, more than genetics, shapes immune system

Is everyone naturally immune to some disease?