Researchers have identified a long-lived population of monocyte-derived cells in the lungs that produce galectin-1 and support tissue-resident memory T cells, offering a promising new strategy for designing effective nasal influenza vaccines that establish lasting local immunity where respiratory infections first begin.
Influenza continues to cause major illness every year in the United States, leading to more than 35,000 deaths annually according to established public health data. Vulnerable populations include children, older adults, pregnant individuals, people with weakened immune systems, and those with chronic conditions such as heart disease, metabolic disorders, and cancer. While vaccination remains the most effective way to prevent flu infection, conventional vaccines delivered via intramuscular injection often fail to stop the virus from taking hold directly in the respiratory tract. Now, a study appearing in Nature Immunology points toward a previously overlooked group of innate immune cells that could fundamentally change how next-generation vaccines are engineered.
Rethinking Immune Memory in the Airways
When an infection or vaccination occurs, the body generates specialized memory cells designed to respond rapidly if the same pathogen returns. In the lungs, a specific category of cells known as tissue-resident memory T cells acts as a first line of defense right where airborne viruses enter the body. These local sentinels are critical for limiting viral spread, but standard injections rarely build robust, durable memory in the airways.
Minsoo Kim, a professor of Microbiology and Immunology at University of Rochester Medicine and lead author of the research, emphasized the importance of these local defenders. These cells are positioned right where infection begins, so they can react immediately and help limit viral spread,
Kim explained. They are a central goal for next-generation vaccine design because they provide fast, local protection in the respiratory tract.
The Persistent Role of Monocyte-Derived Cells
Traditionally, immunologists viewed monocytes as short-lived participants in the initial inflammatory wave. However, the University of Rochester research team discovered that a distinct subset of monocytes persists in the lungs for months following an influenza infection. Rather than fading away quickly, these cells stay behind to maintain the survival and function of tissue-resident memory T cells.
This discovery bridges a major conceptual gap in immunology. This challenges the traditional view that immune memory is driven only by T and B cells, and shows that innate immune cells also play a lasting role,
Kim noted. Beyond influenza, the findings carry implications for other seasonal and pandemic respiratory viruses, proving that innate cells do more than serve as temporary first responders.
Galectin-1 as a Vaccine Adjuvant
The investigation also mapped out the exact biochemical signaling that connects these innate cells to adaptive memory. Researchers determined that the long-lived monocytes produce a protein called galectin-1, which directly sustains tissue-resident memory T cells in the lung environment.
When investigators incorporated galectin-1 into an experimental nasal vaccine tested in mice, the resulting immune response in the respiratory tract grew substantially stronger. We identified galectin-1 as a powerful immune signal that can be used as a vaccine adjuvant to enhance mucosal immunity,
Kim said, describing the approach as a completely new approach for improving how vaccines work in the respiratory tract.
Pediatric Vulnerability and Excessive Inflammation
While adult immune responses often manage influenza efficiently, young populations face distinct physiological risks. Influenza A virus affects up to 40% of children in the United States annually and accounts for the hospitalization of approximately 1 in 1,000 children under the age of 5. During the 2009 H1N1 pandemic, pediatric patients accounted for 33% of all severe respiratory tract infections, with previously healthy children dying at rates comparable to those with high-risk underlying conditions.
Instead, research highlights the host inflammatory response as a primary driver of lung injury. Juvenile subjects display a sustained elevation of type I interferons, prolonged NLRP3 inflammasome activation, and continuous high levels of monocyte chemoattractant protein 1 (MCP-1) even after viral clearance. Experimental depletion of monocytes using an anti-CCR2 antibody successfully reduced interferon secretion, inflammasome activation, and lung injury in juvenile models, pointing toward exaggerated monocyte recruitment as a central mechanism in severe pediatric respiratory illness.
