Hidden lung mechanism could lead to more effective flu vaccines

Published in Nature Immunology, the study suggests that a type of immune cell known as monocytes can remain in the lungs for several months after influenza infection, helping support memory T cells that enable the body to respond rapidly when it encounters the virus again.

A New Role for Immune Cells Traditionally Considered Short-Lived

The researchers, led by Minsoo Kim, a professor of microbiology and immunology at the University of Rochester School of Medicine, investigated how memory T cells form and persist in the lungs after an infection has cleared.

The team discovered that a subset of monocytes—immune cells traditionally regarded as short-lived—can remain in the lungs for an extended period following influenza infection.

Rather than simply persisting, these cells appear to play an important role in maintaining memory T cells within lung tissue, helping them continue to function effectively against the virus.

Kim said the study had identified a long-lived population of monocyte-derived cells in the lungs that plays a crucial role in supporting long-term T-cell immunity.

The findings challenge the conventional view that immune memory depends primarily on T and B cells, suggesting instead that cells of the innate immune system may also contribute to the formation and maintenance of long-term immune memory.

A Molecule That Boosts Immune Responses in the Lungs

The researchers also identified one of the mechanisms through which these cells communicate with memory T cells.

They found that the cells produce a protein known as galectin-1, which helps activate and maintain memory T cells residing in lung tissue.

When galectin-1 was added to an experimental influenza vaccine and tested in mice, researchers observed a significant increase in the strength of the immune response within the lungs.

According to Kim, the finding could open the door to using galectin-1 as a vaccine adjuvant to enhance mucosal immunity in the respiratory system.

A Gap in Protection Provided by Current Vaccines

Vaccination remains the most effective way to prevent influenza and reduce the risk of serious complications. However, most currently available flu vaccines are administered by injection and do not always trigger a strong immune response in the nose and lungs.

This is particularly important because the respiratory tract is the primary entry point for the virus. Having immune cells capable of rapidly recognizing the virus at this site could help contain an infection before it spreads further.

Nasal influenza vaccines are designed to address this challenge by stimulating immunity directly within the respiratory tract. However, their ability to provide strong and long-lasting protection has not always been consistent, prompting researchers to explore new ways of strengthening immune responses in this area.

The study suggests that enhancing interactions between innate immune cells and memory T cells could represent one potential strategy for improving such vaccines.

Potential Implications for Other Respiratory Viruses

The significance of the discovery may extend beyond influenza. Researchers believe that the mechanism identified in the study could also prove useful in developing vaccines against other respiratory viruses responsible for seasonal outbreaks or epidemics.

Kim said the findings show that innate immune cells do not function solely as the body's first line of defense against infection, but may also influence long-term immune memory.

This could eventually allow scientists to design vaccines that take more precise advantage of this previously underappreciated function.

However, the findings are still at an early stage. The results were obtained through experiments in animal models, and it has not yet been established whether the same mechanism operates in humans.

Researchers are now working to develop more stable forms of galectin-1 as they prepare to investigate whether it can be safely used as a vaccine adjuvant.

If future studies confirm that this mechanism is effective in humans, the findings could help reshape the way respiratory vaccines are designed—shifting the focus beyond the production of antibodies throughout the body to also building strong immune memory directly in the lungs, where respiratory infections begin.