Quest begins for common test for immune system health

By the time Dr. Eswar Krishnan, 42, enters his retirement years, he’s confident that his doctor will be able to administer a simple test to gauge his immune system’s strength.

He can forecast the development of this powerful medical tool, which could join other cholesterol and other routine tests in doctors’ offices. The Stanford researcher and two colleagues just launched the largest clinical trial to date to find a common biomarker to assess immune system health. Biomarkers typically are molecules or cells in blood samples that reveal a person’s status for a particular health condition, such as glucose tests that reflect diabetes risk.

“My expectation is when I hit Medicare age, these tests will be available,” Krishnan said.

An immune system test would enhance medical care, said Rebecca Fuldner, a project officer at the National Institute on Aging, which co-funded the $9 million, three-year study. Doctors could tailor vaccination strategies to individual patients, and deliver quick intervention at the first sign of illness for those with weakened immune systems.

Krishnan views an immune test as useful for inspiring healthful habits, such as balanced nutrition and adequate physical activity, both of which boost immune function.

“It will be a stimulus for lifestyle changes, because that is much more powerful than drugs,” he predicted.

Physicians have no way to assess the overall health of a person’s immune system. Yet it declines precipitously with age, leaving older people far more vulnerable to infectious diseases and cancer, and to autoimmune disorders such as arthritis.

For example, levels of critical T cells, the immune cells that serve as the first line of defense against microbial threats, decrease significantly by the sixth decade of life.

With age, other immune cells, such as white blood cells, are more likely to either underreact to a threat, opening the door to disease, or to overreact. In the latter case, the immune cells stay on the attack, rather than retreating to their normal state. This can harm even healthy tissue and cause autoimmune diseases such as lupus and rheumatoid arthritis.

“We want the white cells to get angry, but not too angry,” Krishnan said, speaking metaphorically. “We want them to go back to their baseline state.”

The decline in immune function over a lifetime, called immune senescence, is the reason the elderly are so much more vulnerable to illnesses such as influenza, Fuldner said. The National Institute of Allergy and Infectious Diseases co-funded the study.

Older people also succumb far more readily to new infectious diseases, she said, as their immune system has no “immunological memory” of the novel microbe and cannot mount the robust and adaptive defense of a younger person.

During the SARS outbreak in 2003, for example, mortality reached 90 percent in those 60 and older, Fuldner said. With West Nile virus, she said most of the deaths occur among those older than 50.

In addition, the weakening immune system makes vaccines less effective.

“So it’s kind of a double whammy,” she said. “You can’t vaccinate to protect against the disease, yet they’re more susceptible to it.”

Krishnan’s study will measure the levels of about 100 immune cells and other biomarkers, such as T cells, B cells, dendritic cells and monocytes, and analyze how they differ between the age groups of study participants, and between women and men.

He and his colleagues Dr. Gary Fathman and Dr. Jorg Goronzy will post their database on the immune profile of healthy adults at various ages for use by other researchers. “There’s going to be a lot of information coming out of this grant that will also lead to future studies,” Fuldner said.

Suzanne Bohan covers science. Contact her at 510-262-2789. Follow her at Twitter.com/suzbohan.