Immune Cell Ratio Predicts Healthy Versus Unhealthy Aging

Age alone doesn’t tell the full story of a person’s health, since two people born on the same day can have immune systems that age very differently. Researchers at Washington University School of Medicine in St. Louis, Nationwide Children’s Hospital in Ohio, and King’s College London have built a map of human immune aging that helps explain these diverging paths. The findings, published in Immunity, show that the ratio between two immune cell types can reveal whether someone is on track for healthy aging or at risk of future disease. “We have found that there are clues in the blood that can tell us whether someone is on a healthy or unhealthy aging trajectory,” said co-corresponding author Maxim N. Artyomov. “Identifying specific biological red flags in the immune system could pave the way for early-warning tests that spot disease risks years before a clinical diagnosis.”

The team, including co-corresponding authors Stephen Harridge and Mykyta Artomov, analyzed about 12.4 million individual immune cells from 2,609 mostly healthy adults ages 20 to 90-plus across eight cohorts in North America, the United Kingdom, Asia, and Australia. While younger participants consistently had blood enriched with naive immune cells not yet exposed to pathogens, older participants showed more variation, with some showing a greater abundance of inflammation-linked cells. To track this shift, researchers placed each participant on a spectrum based on the ratio of granzyme B-producing cells to granzyme K-producing cells, two types of effector memory CD8 T cells that use these molecules to destroy diseased cells or coordinate immune responses.

To test whether this ratio predicted future health, the researchers built a computer model using blood protein data and CD8 T cell counts from a smaller cohort, then applied it to baseline blood samples from 50,000 UK Biobank participants tracked for up to 15 years. Healthy adults whose immune systems leaned toward granzyme B cells at baseline had a higher risk of death a decade later and were more likely to develop chronic conditions including Type 2 diabetes, hypertension, liver disease, and renal failure, compared to those with more granzyme K cells. “A higher level of granzyme B cells in a healthy state means the immune system might be already reacting to something,” said coauthor Marina Terekhova. “It isn’t a formal disease diagnosis, but it may indicate the body is off track.” A healthy immune system gradually shifts toward granzyme K cells over time, while a shift toward granzyme B cells signals unhealthy aging, and because people can reach this state at different ages, their immune systems age along different trajectories.

Mapping someone onto this spectrum currently requires specialized, costly technology, so Artyomov’s lab is adapting the research into a simple blood test that could run on standard equipment. “We can think of it like checking a car’s oil level before the check engine light ever turns on,” Artyomov said. “Our goal is to develop an early-warning diagnostic that alerts physicians to subclinical immune stress, prompting more specialized testing that could allow for intervention long before chronic disease symptoms appear.”