Older adults often get much sicker from the flu than younger people, and now scientists have discovered an important reason why.
A new study published in the journal PNAS explains how a natural protein in the body, called apolipoprotein D (ApoD), plays a surprising role in weakening the immune system’s ability to fight flu viruses as people age.
ApoD is a protein that helps with fat processing and inflammation in the body. While it’s useful in some ways, the new research shows that older people produce much more ApoD than younger people—especially in the lungs.
This high level of ApoD makes it harder for the body to defend itself from the flu, which can lead to more serious illness and greater damage to lung tissue.
The study was conducted by an international team of scientists from China Agricultural University, the University of Nottingham, the Institute of Microbiology at the Chinese Academy of Sciences, the Chinese Centre for Disease Control and Prevention, and the University of Edinburgh.
They worked together to understand why older patients are more vulnerable to severe flu.
The scientists used mice that mimic human aging, as well as samples of human lung tissue, to figure out what happens during flu infection. They found that ApoD interferes with a key part of the body’s defense system: type I interferons.
These are special proteins that help the immune system attack viruses early on. When there’s too much ApoD, the production of interferons goes down. As a result, the flu virus can spread more easily in the lungs, causing more inflammation, more virus growth, and more damage.
One reason ApoD causes so much trouble is because it disrupts the function of mitochondria—the tiny power plants in our cells. Mitochondria help cells make energy and also play a role in signaling for the immune response.
When ApoD levels are too high, the mitochondria break down in a process called mitophagy, which weakens the body’s ability to signal the alarm and fight off the virus.
This discovery is important because it shows that ApoD could be a new target for flu treatments. If scientists can find a way to block or reduce ApoD activity in older people during flu infections, they might be able to boost the immune response and protect against serious illness.
This could lead to better outcomes for the elderly, who are most at risk of flu-related complications and death.
Professor Kin-Chow Chang from the University of Nottingham, who co-authored the study, said that the world’s population is aging fast, and flu remains a serious health threat to older adults. By understanding how aging affects the immune response, scientists can develop new ways to keep people healthier for longer.
In summary, this research shows that a natural protein called ApoD increases in the lungs as we age and plays a big role in weakening our defenses against the flu. Blocking this protein could be a powerful new strategy to protect older adults from getting seriously ill. It’s a promising step forward in understanding and treating flu in aging populations.
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