How a person's immune system does its job seems to depend more on environment and the germs he or she encounters than on genes, according to new research.
The immune system adapts throughout life to fight disease, said Stanford University immunologist Mark Davis. And while young children's immunity may be more influenced by what they inherit from their mother and father, this study showed genetic influences waned in adulthood.
"Experience counts more and more as you get older," Davis said.
Davis compared 78 pairs of identical twins with identical genetic makeups to 27 pairs of fraternal twins, who are no more alike genetically than any other siblings. Traits shared by the identical twins are more likely to be hereditary.
His team used blood samples from the twin pairs, who ranged in age from 8 to 82, to track more than 200 activities and components of the immune system. In three-quarters of the measurements, differences between pairs of twins were more likely due to non-heritable influences - such as previous infections or vaccinations, even nutrition - than genetics, the researchers reported in the journal Cell.
Then they compared the oldest twins, 60 and over, to those under age 20, when the immune system is still maturing. The youngest identical twins had far more immune similarity than the oldest. That makes sense, as older twins presumably haven't lived together in years and have had different exposures since childhood, they concluded.