Ever since the human genome was mapped, medical research on immunity has attempted to seek answers about our susceptibility to diseases from our genes. But barring a few exceptions, very few gene variations contribute much to particular health outcomes. Now, a group of researchers at the Stanford University School of Medicine have claimed that immunity is more influenced by environment than genetic make-up, and to a degree greater than that was previously assumed.
Mark Davis and his team conducted twin studies—research involving pairs of monozygotic, or identical (with nearly the same genetic make-up) and dizygotic, or fraternal (sharing about 50% of the genes) twins—and found that immunity is influenced by a person’s environment , increasingly so as she ages. Given twins share the same in utero and near-similar ex utero environments, they make excellent subjects for contrasting hereditary and environmental influences. The Stanford researchers observed 78 monozygotic-twin pairs and 27 pairs of dizygotic twins from a 2,000-strong twin registry maintained over two decades and measured more than 200 immune system components and processes. The researchers found that in over 75% of the measurements, the non-heritable influences such as vaccination, previous microbial exposure, diet, etc, trumped heritable influences. The differences in immune responses grew with the subjects’ age, indicating that the effects of the environment on immunity get more pronounced with age—Davis believes this explains why previous studies suggested a powerful genetic component in an individual’s immune make-up, given these studies were mostly conducted on very young children.