Researchers at UC San Francisco have uncovered a long-sought explanation for why nursing home residents and other older adults so often end up in the hospital — and sometimes on ventilators — when they catch the flu or COVID-19. The answer, it turns out, is buried in the lungs themselves.
A study published March 27 in the journal Immunity found that aging lung cells can trigger a runaway immune response that overwhelms the body — not because the infection itself is unusually severe, but because the lung’s own tissue is primed to overreact.
What the researchers found
The UCSF team, led by pulmonologist Tien Peng, MD, focused on a type of structural lung cell called fibroblasts. These cells normally maintain the lung’s delicate architecture, but in aging tissue, they can send out distress signals even in the absence of serious disease.
To test this, scientists triggered an age-related distress signal in young mice using fibroblasts. The signal caused the lungs to form clusters of inflamed cells — including a cell type marked by the GZMK gene first identified in severe COVID-19 cases. Once that immune circuit fired, the young mice developed severe symptoms from infections they’d normally shrug off — mimicking the vulnerability seen in elderly patients.
“We were surprised to see lung fibroblasts working hand-in-hand with immune cells to drive inflammaging,” Peng said. “It suggests new ways to intervene before patients progress to severe inflammation that can require intubation.”
When researchers eliminated the GZMK-marked cells from the lungs, the young mice were able to withstand the same infections with far less damage.
Why this matters for nursing homes
The findings help explain a pattern that long-term care facilities know well: residents who aren’t critically ill in any obvious way can deteriorate fast once respiratory illness takes hold. What looks like a manageable infection can spiral into ARDS — acute respiratory distress syndrome — within days.
The researchers examined lung tissue from older patients hospitalized with COVID-related ARDS and found the same clusters of inflamed cells they had observed in the mice. Sicker patients had more of these clusters. Tissue from healthy donors had none.
That discovery points to a specific biological circuit — not just “old age” in the abstract — that could one day be targeted with therapies designed to interrupt the damage before it becomes irreversible. As nursing home residents continue to face significant gaps in healthcare coverage, research like this underscores how much the underlying biology of aging shapes their vulnerability.
Looking ahead
The study doesn’t offer a clinical solution yet, but it does narrow the target. A drug or treatment that quiets the NF-kB pathway — the signaling route that triggers the fibroblast distress signal — could potentially protect older patients before a respiratory infection has a chance to spiral.
For nursing facilities that have watched healthy residents deteriorate from flu season after flu season, that kind of targeted intervention can’t come soon enough.
The study was co-authored by Nancy Allen, MD, PhD, a clinical fellow in UCSF’s Pulmonary and Critical Care Division, who served as first author.
