The immune system is meant to protect the body from infection and disease.

But with age, it can become less capable of doing so.

However, Mayo Clinic researchers in the United States have found that some older people maintain “immune youth” – a new term they coined to explain a young immune system in someone over age 60.

“We are studying why some individuals have a ‘fountain of youth’ in their immune systems.

“We want to learn from them,” says rheumatologist and clinician-scientist Dr Cornelia Weyand.

She is a lead author on a perspective paper published in the journal Nature Aging.

Dr Weyand’s research team discovered this cellular fountain of youth in more than 100 older patients who came to Mayo Clinic to receive treatment for an autoimmune disease that affects the arteries, including the aorta, called giant cell arteritis.

They found specialised immune cells, called stem-like T cells, in the diseased tissue of these patients.

These immune cells behave like young stem cells that usually regenerate and aid healing and growth.

But in this case, they were spreading the disease.

This team of researchers also discovered autoimmune stem cells in humans previously.

“We observed that these patients have very young immune systems, despite being in their 60s and 70s.

“But the price they pay for that is autoimmunity,” says Dr Weyand.

Autoimmunity is when the immune system mistakenly attacks healthy tissues and organs.

In addition, the researchers saw that the immune checkpoint inhibitors that regulate the immune system were not working properly.

“Contrary to what one may think, there are benefits to having an immune system that ages in tandem with the body,” says study co-lead author and ageing researcher Dr Jörg Goronzy.

“We need to consider the price to pay for immune youthfulness.

“That price can be autoimmune disease.”

Immune ageing is a sophisticated adaptation mechanism that the immune system can use to prevent autoimmune disease, say the researchers.

They are in the process of developing new diagnostic tests that will help find patients and healthy individuals who carry high numbers of immune stem cells and may be predisposed to autoimmune disease later in life.

The research is part of a larger effort at the Mayo Clinic called the Precure initiative, which is focused on developing tools that empower clinicians to predict and intercept biological processes before they evolve into disease or progress into complex, hard-to-treat conditions.