The immune systems of two people of the same age can age differently, affecting their risk of developing chronic diseases and dying prematurely. Researchers from Washington University School of Medicine in St. Louis, Nationwide Children's Hospital in Ohio, and King's College London have identified biological markers that may help assess how well the immune system is aging.
The findings were published in the journal Immunity. The authors suggest that their discovery could eventually lead to a blood test capable of identifying an increased risk of disease at an early stage, before symptoms appear.
The scientists analyzed approximately 12.4 million individual immune cells obtained from blood samples from 2,609 predominantly healthy people aged 20 to 90 and older. The participants represented eight research cohorts from North America, the United Kingdom, Asia, and Australia.
In younger people, naive immune cells predominated in the blood. These cells have not yet encountered specific pathogens and retain the ability to respond to new infections and vaccines. Among older participants, the picture was more varied: some had higher proportions of immune cells associated with inflammatory processes.
To assess differences in immune aging, the researchers examined the ratio of two types of cells — those producing granzyme B and those producing granzyme K. These proteins are involved in the functioning of certain white blood cells, particularly effector and memory CD8 T cells. Granzyme B helps destroy damaged or infected cells, while the role of granzyme K is less well understood. It is thought to be involved in signaling processes that recruit other components of the immune system.
An analysis of participants' subsequent health records showed that people whose immune systems initially contained a predominance of granzyme B-producing cells had a higher risk of death in the following years. They were also more likely to develop chronic conditions, including type 2 diabetes, hypertension, liver disease, and kidney failure.
According to the researchers, the relative role of granzyme K-producing cells gradually increases in the immune system with age. A predominance of cells associated with granzyme B may indicate a less favorable trajectory of immune aging. Because such changes can occur long before old age, people of the same age may differ substantially in their risk of developing chronic diseases.
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