Immune systems in humans are shaped more by environment and behavior than by genetics, according to a new study. Past exposure to pathogens, as well as a record of immunizations, appears to hold a greater influence over health and wellness than genes, according to the new study.
The human immune system is incredibly complex, including a wide variety of white blood cells, as well as messenger proteins to coordinate attacks on microbial invasions. The overall makeup of immune systems can differ greatly from person to person, based on both genetic and environmental factors.
Twins were studied in the experiment, in an effort to determine the relative roles played in illness and health by environment versus heredity. Identical twins share an almost identical set of genes, whereas about half of the genetic code matches in fraternal twins. This allows researchers to isolate which aspects of a subjects health are due to genetic inheritance, as opposed to environment.
Mark Davis of Stanford University led the research team, which studied blood samples from 210 twins, both fraternal and identical, between the ages of eight and 82. These were then examined, searching for 200 factors related to health, including 51 varieties of proteins and 95 forms of immune cells. Investigators found that the immune systems of identical twins were too varied to be explained by genetics. In three quarters of the experiments performed, environment was found to be the predominant factor over genetic inheritance.
"Moreover, younger twins were more similar than were older twins, evidence that as the twins aged and were exposed to different environments, their immune systems diverged over time," Emily Conover wrote for Science magazine.
Flu vaccines were studied as part of the research, as identical twins should have nearly-identical immune responses if genetics were the dominant factor in fighting illness. The study found that there were significant differences in how bodies of identical twins responded to the vaccines. The degree to which antibodies, forms of protein used to fight off disease, are created in a body appeared to be primarily related to environment. This difference is likely related to the strains of influenza to which a person had become exposed during their lifetime.
Cytomegalovirus (CMV) is a highly-contagious, but usually harmless, virus related to chicken pox and infectious mononucleosis. Between 50 and 80 percent of the U.S. population carries the microbe in their systems. Some of the identical twins in the study were pairs where only one of the siblings carried CMV. Researchers found great variation in those pairs, highlighting the role of environment in shaping immune system responses.
Variation in the Human Immune System Is Largely Driven by Non-Heritable Influences, an article detailing the study, was published in the journal Cell.
