Social stress is known to have adverse health effects on both humans and primates.

Now, researchers report that it also affects the immune system of female rhesus macaques at the genetic level.

''Social stress seemed to have a relatively strong and pervasive effect on the regulation of the genome,'' said Jenny Tung, an evolutionary anthropologist now at Duke University who studied the macaques as a postdoctoral fellow at the University of Chicago. She is the first author of a study that appears in the current issue of the Proceedings of the National Academy of Sciences.

Dr. Tung and her colleagues found differences in the expression of nearly 1,000 genes in the white blood cells of macaques. They focused on the monkeys' T cells and other white blood cells that play a role in immunity.

''Although all of the monkeys have the same set of genes in their white blood cells, not all of them turn on these genes to the same degree,'' Dr. Tung said.

Dr. Tung and her colleagues were able to predict the social ranking of a female macaque with 80 percent accuracy simply by looking at the genes.

They worked with 49 macaques at the Yerkes Primate Research Center at Emory University.

They also found that if a macaque's social rank changed, her gene expression did as well.

''If an individual is able to improve their social environment, the genome is pretty plastic, which is kind of optimistic,'' Dr. Tung said.

She said the results could provide insight into how to manage stress caused by social status in humans.

PHOTO: Researchers found they could predict a female macaque's social ranking by looking at its genes. (PHOTOGRAPH BY NATIONAL PRIMATE RESEARCH CENTER)