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.
That's the finding of new research that put twins to the test to find out.
The research was led by Stanford University immunologist Mark Davis. Scientists know there is tremendous variation in how the immune systems of healthy people function, but Davis asked if that was more a matter of nature or nurture.
He compared 78 pairs of 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.
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Davis' 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.
The researchers then 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, the researchers concluded, as older twins presumably haven't lived together in years and have had different exposures since childhood.
When the researchers gave flu vaccine to participating twins, they found no sign that genetics determined how many flu-fighting antibodies were produced.
The study was published on Thursday in the journal Cell.
