The immune system is constantly adapting to fight off disease, learned researchers. And while some facets of immunity are passed on from parents to children, what these children encounter throughout their lives is what really counts. Immunity is gradually learned throughout one's life, in other words, and not instantly set in stone after birth.
"Experience counts more and more as you get older," said Stanford University immunologist Mark Davis, the man who headed up this latest work.
Davis and his team set out to determine whether immunity is more a function of nature or nurture, and they did this by comparing 78 pairs of identical twins. They also looked at 27 pairs of fraternal twins, which unlike identical twins are not a perfect genetic match. Traits shared by identical twins are said to be primarily hereditary rather than learned.
Researchers took blood samples from all the twins, who ranged in age from eight to 82 years, and looked at more than 200 variables and activities associated with their immune systems. In 75 percent of measurements, observable differences between pairs of twins were found to be more than likely due to non-hereditary influences such as nutrition, previous infections or previous vaccinations.
Only 25 percent of measurements, on the other hand, suggested any sort of hereditary link. This was further illustrated by comparisons made between the oldest twins, 60 and over, and the youngest twins, under age 20. The younger twins, whose immune systems had not yet fully developed, were found to be remarkably similar immune-wise, while the older twins had immune systems that were more variant.
This makes sense, as many twins tend to grow apart as they get older and embark upon their own individual lives. As a result, they are exposed to different things, including different environmental conditions, different viruses and bacteria, and different medicines and treatments, all of which alter and shape the immune system.
Natural exposure to germs is good for the immune systemSimilarly, when the research team administered flu vaccines to participating twins, they observed no clear signs that genetics played any role whatsoever in how many antibodies were produced. It all comes down to individual exposures, diet and other lifestyle factors that influence immunity and ultimately determine whether or not a person will succumb to disease.
Even when one person in a twin pair was exposed to a virus -- in the case of this study, cytomegalovirus, or CMV -- there were obvious non-genetic variants between the infected and the uninfected to further suggest that "nurture" is a more important health factor than "nature." Of the 16 pairs of identical twins analyzed, where one twin had CMV and the other didn't, researcherS noted major differences in nearly 60 percent of the components studied.
With this in mind, avoiding germs, which we are all told to do to stay healthy, may actually cause more harm than good. Early exposure to germs can help prime the immune system, much like how vaccines are supposed to work. When these exposures don't occur, immunity is weakened.
"I'm a strong believer in the power of dirt," added Davis. "This [study] just says the environment plays a huge role in shaping what your immune system looks like."
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