Older people often get very sick from the flu or COVID. New research from the University of California, San Francisco explains why. The scientists found that lung cells get older and start a too‑strong immune reaction, turning a mild infection into a serious illness.
This discovery helps us understand why a simple cough can sometimes lead to a hospital stay for seniors.
Aging Lung Cells Cause Inflammation
To see what changes in old lungs, researchers looked at fibroblasts. Fibroblasts are cells that hold lung tissue together. In young mice, the scientists turned on a stress signal that usually appears with age. The lungs then filled with groups of inflamed cells, some of which carried a gene called GZMK that was first seen in severe COVID‑19 cases. Future medicines might target these cells to stop the harmful “inflammaging” cycle.
"We were surprised to see lung fibroblasts working together with immune cells to drive inflammaging," said Dr. Tien Peng, a professor of Medicine at UCSF. "It suggests new ways to step in before patients need a ventilator."
Immune System Interaction
Fibroblasts and the NF‑kB Pathway
Fibroblasts keep airways and air sacs strong. But they can also cause inflammation, such as in COPD. The team wanted to know if signals from fibroblasts could upset healthy lungs.
They studied a pathway called NF‑kB, which is linked to many age‑related diseases. When this pathway turned on, fibroblasts told lung macrophages to start an immune response. The response attracted more immune cells from the blood, including the GZMK‑marked cells.
Even though GZMK cells do not fight infections well, they still hurt lung tissue.
Immune Cell Clusters Damage Lungs
After the immune clusters formed, the young mice got very sick when infected, looking like older humans do. When researchers removed the GZMK cells using genetics, the mice handled the infection better.
This shows that aging lung tissue itself may drive harmful inflammation.
The scientists also looked at lung tissue from older patients who were in the hospital with COVID‑related ARDS. Those lungs had the same inflamed cell clusters seen in the mice. Patients who were sicker had more clusters, while healthy donor lungs had none.
"During COVID we saw our most vulnerable patients no longer had the virus, but they still had dangerous lung inflammation," Dr. Peng explained. "This broken circuit between lung and immune cells gives us a promising new target for treatment."