A new study says our environment more than heredity plays a significant role in determining the health of our immune system.

Research indicates the condition of our immune system becomes visible as we age. After all, the immune system adapts throughout life to fight disease, said lead author and Stanford University immunologist Mark Davis.

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On the other hand, young children's immunity may be more influenced by what they inherit from mom and dad. Genetic influences diminish in adulthood, however.

Experts are aware there's an overwhelming variation in how the immune systems of healthy people work. Davis and the team compared 78 pairs of twins with identical genetic make-ups to 27 pairs of fraternal twins, who are no more alike genetically than any other siblings.

They found out that traits shared by the identical twins are more likely to be hereditary.

His team used blood samples from the twin pairs (age 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 because of non-heritable influences such as previous vaccinations and nutrition compared to genetics.

They compared results to the oldest twins (60 and over) when the immune system is still maturing. The youngest identical twins had similar immunity to the oldest. Researchers concluded this was because older twins presumably haven't lived together in years and have had different exposures since childhood.

When the researchers gave flu vaccines to the participating twins, they discovered no signs that genetics determined how many flu-fighting antibodies were produced.

The study also revealed that infection with a virus so common that most adults unknowingly carry it had a huge effect. Cytomegalovirus (CMV) is dangerous to those with weak immune systems but harmless for most people, and prior research has shown it can boost parts of a healthy immune system.

The Stanford team examined 16 pairs of identical twins where only one had CMV. They found big differences in nearly 60 percent of the components studied.

TagsEnvironment, immune system, Genetics, Twins, identical twins, fraternal twins, Cytomegalovirus