Immunity is created, not genetically determined

Some people do better than others at fighting the flu, and you might suspect they were born with that ability.

New research disproves the belief that the strength of the body’s immune system is genetically programmed.

In one of the most comprehensive analyzes of immune function performed to date, researchers analyzed blood samples from 105 pairs of healthy twins.

They measured cell populations of the immune system along 204 parameters before and after all study participants received a flu shot.

Differences in three-quarters of these parameters depend less on genetics than on environmental factors such as diet and previous infections.

Genetic predisposition had almost no effect on how the bodies of the people studied responded to the flu shot, as judged by the antibodies produced against the injected material.

It turns out that twins who have the same genome have strikingly different immune functions. This phenomenon was more pronounced in older twin pairs than in younger ones.

Findings published in the journal Cell show that lifestyle habits have a greater effect on the strength of the immune system than the DNA passed down from our parents.

Although two earlier separate studies indicated that non-hereditary factors contribute to some autoimmune diseases such as multiple sclerosis, the latest analysis is one of the first to quantitatively examine genetic factors and the influence of the environment on the general state of the immune system.

“We were surprised by the degree of environmental influence on so many components,” says Mark Davis of Stanford University Medicine, senior author of the new study.

One discovery is particularly impressive. The factor such as previous cytomegalovirus infection affected 58 percent of the studied parameters.

While the results don’t show whether these changes cause a stronger or weaker immune response, they show that “cytomegalovirus has a really huge effect,” Davis says. Epstein-Barr virus, another microbe that commonly infects humans, had no such effect.

The profound impact of cytomegalovirus on the immune system is perhaps less shocking. “In order to survive, viruses must pass through physical and innate barriers.

The fact that the virus is still active means it’s very good at what it does,” says Peter Barry, a biologist who studies cytomegalovirus at the University of California.

Actually, cytomegalovirus affects all parts of the human body. Yet even though more than three out of five adults have been infected with the germ, they didn’t know it.

This is because about one-tenth of a person’s circulating T cells are specific for cytomegalovirus. “It takes an absurd amount of our immune system’s strength to neutralize this virus,” says Barry.

Scientists are not sure why the Epstein-Barr virus, which also infects most people and persists in the body, does not elicit as strong an immune response as it does with cytomegalovirus.

The explanation may be that Epstein-Barr virus infects a specific type of cell, while cytomegalovirus can hide in a variety of cell types.

Some researchers believe that the presence of cytomegalovirus is why older people tend to respond poorly to the flu vaccine. T cells develop in the thymus, but this gland shrinks with age, slowing the production of new T cells.

As we age, an increasing proportion of T cells are used up by cytomegalovirus, and so cells remain less available to fight seasonal infections.

But there is also evidence that cytomegalovirus has some benefits. Research in mice shows that animals infected with cytomegalovirus cope better with bacterial pathogens.

And in a study of monkeys, researchers found that a cytomegalovirus-based vaccine protected 50 percent of animals from simian immunodeficiency virus infection.

Seeing the effect of this microbe’s activity, scientists recommend caution when interpreting DNA tests that claim to predict risk for a host of diseases from Alzheimer’s to cancer.
“Genome sequencing will not to tell you everything about your health,” says Davis. “There’s a whole dialogue that goes on between your genome and your environment.”