The Missing Gut Protein That May Set the Stage for Peanut Allergy

Peanut allergy affects an estimated 1.6 million children in the United States (NIAID), and for most families the first warning sign is the first exposure, a reaction that seems to arrive out of nowhere. A new study suggests some of the groundwork for that reaction may be laid years earlier, inside the gut lining itself, before a child's immune system ever meets a peanut protein. Researchers at the University of North Carolina at Chapel Hill found that mice bred to be susceptible to peanut allergy are completely missing a specific antimicrobial protein in their small intestine, and that children with peanut allergy show a version of the same deficiency in biopsies of their own gut lining.

Key Takeaways

• Mice genetically prone to peanut allergy are completely missing lysozyme, an antimicrobial protein normally made by Paneth cells (specialized gut cells that help police intestinal bacteria), in their small intestine, even before any peanut exposure.
• Small intestinal biopsies from 3 children with peanut allergy showed fewer lysozyme-producing crypts than biopsies from 5 children without the allergy.
• The missing protein traces to a genetic deletion, not just low activity, and was linked to shifts in gut bacteria in the mice.
• The finding comes from one mouse strain and a small group of pediatric patients already undergoing endoscopy for other reasons, so it shows a link, not proof that the gut defect causes peanut allergy in people.

Paneth Cell Protein Lysozyme Is Missing in Allergy-Prone Mice

Mice from a strain bred to develop peanut allergy are completely missing lysozyme (an antimicrobial protein that kills bacteria by breaking down their cell walls) from the Paneth cells (specialized gut cells, at the base of intestinal glands, that secrete antimicrobial compounds to keep gut bacteria in check) of their small intestine, according to a study published in Cellular and Molecular Gastroenterology and Hepatology. Researchers at the University of North Carolina at Chapel Hill built a single-cell atlas, a map of gene activity across thousands of individual gut cells, comparing CC027 mice, which are prone to peanut allergy, to C3H/HeJ mice, a strain that resists developing it through the gut. In their peanut-naive, baseline state, before any allergen exposure, CC027 mice's Paneth cells showed zero detectable activity of Lyz1, the gene that codes for lysozyme, along with visible cell stress under electron microscopy, including swollen internal compartments and misshapen secretory granules.

The gap is not simply the gene being switched off. The CC027 strain's copy of the chromosome region containing Lyz1 traces back to a Collaborative Cross founder strain, CAST/EiJ, that does not carry a working version of the gene at all, so lysozyme is structurally absent, not just suppressed. The researchers also documented other shifts in the gut lining of allergy-prone mice: fewer interferon-responsive absorptive cells, fewer hormone-producing enteroendocrine cells, and more mucus-making goblet cells and sensory tuft cells, compared to the resistant strain.

Why This Matters for Families Managing Peanut Allergy

Peanut allergy is one of the most common and potentially life-threatening food allergies in children, and doctors currently have no reliable way to identify which infants will go on to develop it before symptoms appear. A growing body of research already links breakdowns in the gut lining to food allergy more broadly (intestinal epithelium and food allergy). If a detectable gut signature, like missing lysozyme, turns out to precede allergy development in people the way it does in these mice, it would reframe peanut allergy as something partly set up inside the gut before a child's first bite, rather than a reaction that develops only on exposure. That matters most for parents of infants at elevated allergy risk, such as those with eczema or an existing food allergy, who are already navigating early-exposure guidance from allergists.

How Researchers Tested Mice and Human Biopsies

To build their atlas, the researchers sequenced gene activity in individual jejunal (mid small intestine) epithelial cells from three peanut-naive CC027 mice and three peanut-naive C3H/HeJ mice, all female, identifying 13 distinct cell types, and confirmed the Paneth cell and lysozyme findings with electron microscopy and antibody staining. To check whether the mouse finding said anything about people, the team examined small intestine (duodenal) biopsies from 8 pediatric patients at UNC, 5 without peanut allergy and 3 with it, all already undergoing endoscopy for unrelated symptoms such as weight loss, difficulty swallowing, or eosinophilic esophagitis (an inflammatory esophagus condition often linked to food allergies). Biopsies from the patients with peanut allergy showed fewer lysozyme-positive crypts than biopsies from those without it.

What This Could Mean, and What It Does Not Prove Yet

For now, this is not a test parents can ask for, and no supplement or intervention has been shown to raise gut lysozyme or change allergy risk. The study's main value is mechanistic: it points to a specific missing protein and a plausible pathway to peanut allergy. The researchers found that CC027 mice shared several enriched gut bacterial groups, including Ruminococcus and Akkermansia, with a separate line of lysozyme-deficient mice from earlier published work, suggesting the missing protein itself is reshaping the gut's bacterial community. Paneth cell lysozyme has also been described in prior research as supporting immune tolerance and gut homeostasis (Paneth cells and intestinal health), fitting a model where its absence tips the immune system toward the allergic, Th2-skewed response seen in food allergy. None of this is established in people; anyone concerned about a child's allergy risk should rely on their allergist's guidance, not this study.

A Small, Lopsided Human Sample Is the Key Limitation

The human portion of the study is small and was not designed as a standalone comparison: all 8 patients were already undergoing endoscopy for other gastrointestinal complaints, not recruited as healthy controls, and the allergy and non-allergy groups had overlapping diagnoses like eosinophilic esophagitis. The authors note this overlap and suggest it reflects shared biology rather than a confound, but the biopsy finding remains a correlation in a small, clinically complex group, not a clean before-and-after comparison. The mouse findings come from a single genetically engineered strain, and no experiment here tested whether restoring lysozyme changes allergy outcomes in mice or people.

What Comes Next for Gut Barrier Research in Food Allergy

The team plans to expand the human side of the work into a larger patient panel to study how intestinal lysozyme, gut bacteria, and immune cells interact in peanut allergy. This same UNC group previously linked the CC027 model to other markers of gut barrier dysfunction in peanut allergy, and this atlas builds on that earlier work. The authors frame their longer-term goal as gut-barrier-targeted therapies, though any such treatment remains early-stage and unproven.

Common Questions

What is lysozyme, and why would losing it matter for allergies? Lysozyme is an antimicrobial protein, normally made by Paneth cells in the small intestine, that breaks down bacterial cell walls and helps keep the gut's resident bacteria in balance. Losing it entirely was linked to shifts in gut bacteria and immune signaling in the allergy-prone mice in this study.

Could this finding predict whether my child will develop a peanut allergy? Not based on this study alone. The mouse strain used is a specific lab model, and the human comparison involved only 8 children already undergoing endoscopy for other reasons, so there is no validated test derived from this work.

Is a missing gut protein the same as poor digestion or low stomach acid? No. This finding concerns a genetic gap in one antimicrobial gene, Lyz1, inside a specific cell type in the small intestine, not a general digestive issue.

Does this research point to a new peanut allergy treatment? Not yet. The study's authors describe gut-barrier-targeted therapies as a future direction, but no treatment or supplement based on lysozyme has been tested in this paper.

References

1. Katelyn M. Clough, Ismael Gomez-Martinez, Gabrielle Cannon, et al. (2026). Single-Cell Mapping of the Gut Epithelium Reveals Paneth Cell Dysfunction and Lysozyme Deficiency in Peanut Allergy. Cellular and Molecular Gastroenterology and Hepatology. https://doi.org/10.1016/j.jcmgh.2026.101914
2. Food Allergy – NIAID. NIH. https://www.niaid.nih.gov/diseases-conditions/food-allergy
3. Ayesha Ali, HuiYing Tan, Gerard E. Kaiko (2020). Role of the Intestinal Epithelium and Its Interaction With the Microbiota in Food Allergy. Frontiers in Immunology. https://doi.org/10.3389/fimmu.2020.604054
4. Charlotte Wallaeys, Natalia Garcia‐Gonzalez, Claude Libert (2022). Paneth cells as the cornerstones of intestinal and organismal health: a primer. EMBO Molecular Medicine. https://doi.org/10.15252/emmm.202216427
5. Erin C. Steinbach, Johanna M. Smeekens, Satyaki Roy, et al. (2022). Intestinal epithelial cell barrier dysfunction and elevated Angiopoietin‐like 4 identified in orally susceptible peanut allergy model. Clinical & Experimental Allergy. https://doi.org/10.1111/cea.14248