BEIJING, April 15 (Xinhua) -- Chinese scientists have developed a new tool to measure how fast the human immune system ages, and identified a key factor that could help slow this process.

The study, led by a research team from the China National Center for Bioinformation and the Institute of Zoology, both under the Chinese Academy of Sciences, and Quzhou Affiliated Hospital of Wenzhou Medical University in east China, was recently published in the journal Immunity.

As people grow older, their immune system weakens, making them more vulnerable to disease. However, measuring the pace of immune aging has long been challenging due to the system's high complexity.

To tackle this problem, the team collected blood samples from 230 healthy people spanning a 60-year age range. They generated a high-resolution map of nearly 1.2 million peripheral blood mononuclear cells and identified 24 distinct immune cell subtypes. Using this data, they built the Human Immune Aging Clock (HIAC), which can estimate a person's immune age with an average error of just 5.66 years.

The study found that T cells, a type of immune cell, are the sensitive indicators of immune aging. The analysis revealed that aging brings profound changes to the immune system, marked by a sharp decline in naive T cells, which are young cells primed to fight new infections, along with an increase in exhausted T cells and monocytes.

The researchers also identified a critical turning point: a major peak in immune aging changes occurs at around age 40, suggesting that midlife is a key period when the immune system begins to decline faster.

Notably, the team found that a factor called RUNX1 plays a crucial role in keeping T cells youthful. Levels of RUNX1 decline with age. When the scientists removed RUNX1 from young T cells, those cells began to show signs of aging. In contrast, when they added more RUNX1 to old T cells, the cells became younger again -- regaining their ability to fight infections.

The researchers said they have confirmed these results in mouse tests: aged T cells that received extra RUNX1 remained younger and functioned better.

According to the study, this discovery makes RUNX1 the first validated internal target for slowing T-cell aging, paving the way for new therapies to help keep the immune system strong in older people. ■