Scientists at the University of Rochester Medical Center have identified a group of immune cells that settle in the lungs for months after a flu infection and quietly help the body remember how to fight the virus. Current injected flu shots largely bypass them.
The findings, published in Nature Immunology, point to a specific protein made by these cells, galectin-1, that acted as a booster when added to an experimental nasal vaccine in mice.
What the researchers actually found
The team followed a subset of monocytes, immune cells that were long assumed to live only a short time in tissue. Instead, the cells stayed put in mouse lungs for more than four months after infection and produced galectin-1, a signaling protein that keeps tissue-resident memory T cells alive and ready to respond.
Those T cells sit in the airway lining and are the body's first defense against a respiratory virus. Without a steady supply of galectin-1, they fade.
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Minsoo Kim, professor of microbiology and immunology at the University of Rochester Medical Center, leads the group behind the work. In a summary of the research from the university's press office, Kim said the cells "are positioned right where infection begins, so they can react immediately and help limit viral spread," and added that the finding "challenges the traditional view that immune memory is driven only by T and B cells."
Why current flu shots leave a gap
Standard injected flu vaccines are designed to prime antibodies in the blood. They cut the risk of severe illness and hospitalization, but they do not build much lasting protection inside the airways themselves, which is where the virus first lands.
That is one reason researchers have chased a nasal flu vaccine for years. The idea is to train immunity in the exact tissue that gets infected. So far the results have been mixed. As Kim put it in the same release, "existing nasal vaccines often fail to generate strong or durable protection."
The new study offers a possible reason. If nasal vaccines do not activate the resident cells that produce galectin-1, the memory T cells needed to hold the front line in the lung never fully take root.
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The mouse test
When the researchers added galectin-1 to an experimental nasal flu vaccine in mice, the immune response in the lungs became significantly stronger, according to a report on the study in GEN. The protein appears to work by making CD8 T cells more sensitive to a growth signal that helps them settle in tissue.
The result is preliminary and comes from an animal model. It has not been tested in people, and the path from a mouse experiment to a licensed vaccine typically takes years and multiple clinical trials.
Why the timing matters
The work lands as the United States heads into flu season. The 2024-2025 season was the worst in more than a decade. Preliminary CDC estimates put the toll at 43 million to 73 million symptomatic illnesses, 560,000 to 1.1 million hospitalizations and 38,000 to 99,000 deaths, with the overall hospitalization rate the highest since the 2010-2011 season. Older adults, young children, pregnant people and those with chronic conditions carried the heaviest burden.
Newer flu shots are already reaching high-risk groups. Moderna's mRNA flu vaccine was cleared for older adults ahead of the 2026-2027 season, expanding the toolkit for the population most likely to end up in the hospital.
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The Rochester team's discovery does not change what is available at the pharmacy this fall. It does, however, hand vaccine developers a specific molecular target, galectin-1 as an adjuvant, to test in the next generation of nasal formulations. Anyone with symptoms or concerns about which flu shot fits them should raise it with their doctor or pharmacist during this year's vaccination visit.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.