Scientists identify unique immune cells that may explain why allergies are more common in urban children than in farm-raised peers

Rochester, New York – Why do kids growing up in cities seem to suffer from allergies more than those raised in the countryside? A new study led by scientists at the University of Rochester Medical Center (URMC) offers an eye-opening explanation—and it has everything to do with the immune system’s early development.

Published in the journal Allergy, the research points to a specific group of immune cells that could be behind the growing rates of allergic diseases in urban populations. This newly identified subset of T cells, called helper 2 (Th2) cells, appears to be more active—and more aggressive—in children who grow up in city environments. According to researchers, these cells could hold the key to understanding why allergies are more common in urban children compared to their rural peers.

“These pro-allergic T cells are more inflammatory than anything previously described in this context,” said Dr. Kirsi Järvinen-Seppo, chief of Pediatric Allergy and Immunology at UR Medicine Golisano Children’s Hospital. “They were found more frequently in urban infants who later developed allergies, suggesting they may be a predictive biomarker or even a mechanistic driver of allergic disease.”

The study’s lead authors include MD/PhD student Catherine Pizzarello and Järvinen-Seppo herself, who has been a longtime investigator in the field of pediatric allergy. Together, the team took blood samples from two very different groups of infants: babies from urban areas and babies from a farming community—the Old Order Mennonites (OOM) living in New York’s Finger Lakes region. The difference in their immune profiles was striking.

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Infants from urban areas showed significantly higher levels of the Th2 cells. These cells, rather than fighting off actual infections, appeared to be mistakenly identifying harmless substances—like food or pollen—as dangerous, triggering unnecessary and sometimes severe allergic responses. On the other hand, babies from the OOM community had more regulatory T cells, which help keep the immune system calm and balanced.

What’s behind this major immune difference? One possible factor, the researchers believe, is early-life exposure to microbes.

“The farming environment, which is rich in microbial exposure, appears to support the development of a more tolerant immune system. Meanwhile, the urban environment may promote the emergence of immune cells that are primed for allergic inflammation,” said Järvinen-Seppo.

In other words, the very cleanliness of urban living could be making children more vulnerable to allergies. From air-filtered homes to antibacterial products, city life might limit the exposure infants have to the types of microbes that actually help build a resilient immune system. In contrast, farm environments—with animals, unfiltered air, and plenty of dirt—may offer a kind of natural immune training ground.

This research is part of a much larger effort supported by the National Institutes of Health. In 2023, Järvinen-Seppo’s team was awarded a $7 million grant from the National Institute of Allergy and Infectious Diseases to explore exactly how differences in environment, microbiomes, and immune responses affect allergy development in children. Their long-term goal is to figure out how to replicate the protective factors seen in rural children and use that information to help kids in urban settings.

“If we can identify the conditions for this disparity between the different T cell subpopulations, we can potentially find solutions in allergic disease development,” Järvinen-Seppo said.

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One possible solution could involve probiotics or microbiome-based therapies—treatments designed to restore or boost the “good” bacteria that help train the immune system to behave more appropriately. Another approach might involve targeted interventions in early childhood to mimic the microbial exposures common in farming environments.

For now, the research is ongoing, but the implications are significant. As allergy rates continue to rise—especially among urban populations—understanding the role of the immune system in early life could be the first step in reversing the trend.

The findings suggest that where a child is born and raised may matter far more to their long-term health than previously realized. With further study, scientists hope to turn this knowledge into practical strategies that protect all children, regardless of zip code, from the burden of allergic disease.