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Environment affects immunity more than genetics

As part of the perennial and never-ending nature versus nurture debate, a new piece of research comes down heavier on the nurture side by indicating that an individual’s immune system is more strongly influenced by environmental factors than genetics. As with many such studies, twins have been used for the assessment.

Earlier research has shown how the most critical aspects of the immune system develop within the first few months in a baby’s life. Part of a healthy immune system comes from a baby’s genes, some from the mother (such as through breast milk) and the rest from the external environment. As the child progresses, the influence of the environment decreases. Nonetheless, what happens over the course of life continues to remain of interest to medics.

The new research provides greater evidence to the theory of the environment. The research shows that how humans respond to the pathogens they encounter through life has less to do with genetics than with their previous exposure to viruses and bacteria (and how effectively the body has responded to these infectious agents.)

By measuring over 200 immune system parameters—such as blood protein levels or the number of immune cells — in 210 identical or fraternal twins, a research group found that environmental factors were more influential than genetic ones in determining the variation between twins more than 75 percent of the time. Identical twins have the same DNA; however, they may not look exactly identical to one another because of environmental factors such as womb position and life experiences after being born. Fraternal twins are not identical.

Furthermore, with over half of the measured parameters, environmental influences accounted for most of the difference. The study participants ranged in age from 8 to 82 years old, and the younger twins, who were more likely to have been exposed to the same environment as each other, showed greater similarities in their immune systems than older ones. This further reinforced the argument that exposure to environmental factors matters most.

One of the largest environmental causes of immune differences between the twins was the presence cytomegalovirus. This is a usually harmless chronic infection, and one harbored by around three in five U.S. citizens. Sixteen of the 27 pairs of identical twins had one infected with this virus, as well as one non-infected twin. In these cases, the researchers found that the cytomegalovirus exposure alone explained over half of the differences between the two siblings’ immune systems.

In a research brief, lead scientist, Mark Davis of Stanford University, stated: “What we found was that in most cases, including the reaction to a standard influenza vaccine and other types of immune responsiveness, there is little or no genetic influence at work, and most likely the environment and your exposure to innumerable microbes is the major driver.”

The study of twins has been published in the journal Cell. The research paper is titled “Variation in the Human Immune System Is Largely Driven by Non-Heritable Influences.”

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