What plays a bigger role in human immune system development: genetics or the environment?

To find an answer, a group of researchers closely analyzed the immune system of pairs of twins. They looked at identical twins, who have nearly the same genetic makeup, and fraternal twins, who share about half their genes.

The scientists drew blood from every study participant. For each set of twins, they compared the same characteristics. These included factors like the number of each different type of immune system cell, levels of proteins the system produces and levels of antibodies created in response to the flu vaccine. For some pairs, they also looked at the amount of a specific virus present.

Differences in these characteristics between identical twins meant those particular factors were influenced most by environment… otherwise, they should match. For non-identical twins, they evaluated the characteristics in light of a model that predicted about how many factors should be attributable to heredity or environment.

For each factor, researchers found varying degrees of matches between twins. So, varying degrees of responsibility could be attributed to genetics or environment.

The overall winner for most influence on these various determinants of immunity was, as the researchers termed it, “non-heritable influences.”

Another notable observation they made: Older sets of twins generally had less similarity in their immune systems. The scientists wrote that this makes the case for environment as the primary shaper of immunity. As the twins aged and their surroundings and experiences became less alike, their immune systems followed suit.

Perhaps future studies will show which parts of our lives are most helpful in creating a balanced, beneficial immune system.