It's been proposed that changes in the immune system may account for age-related changes in the body. Therefore, a logical place to look for a biomarker of aging is within the complex system of cells that make up the immune system.

One investigator- Richard A. Miller, at the Department of Pathology and Geriatrics Center, University of Michigan School of Medicine-has identified T cell subsets that appear to have some predictive power, at least in mice.

T cells are a part of the immune system that patrol for foreign substances, such as bacteria and viruses, that can cause disease in the body. They can also attack and destroy diseased cells, and they orchestrate, regulate, and coordinate the overall immune response. There are several subsets of T cells.

In a study by Dr. Miller, seven T cell subsets were measured in young mice (8 months old) and then were measured again when the mice reached middle age (18 months). Four of the subsets (CD4, CD4 memory, CD4 naive, and CD4 cells expressing P-glycoprotein) were found to predict longevity. Dr. Miller has conducted further research showing that it's possible to combine certain values for T-cell subsets and come up with a single number that is a predictor of life span even as early as 8 months of age in mice. (An 8-month-old mouse is equivalent to a human in his or her 20s).

These findings have not yet been tested in humans. But, according to Dr. Miller, T-cells change in parallel ways between mice and humans. Therefore, age-sensitive changes in T-cell subset patterns appears to be a promising target for a potential biomarker of aging.