Redefining Gluten Thresholds in Celiac Disease: The Role of Interleukin-2 as a Biomarker for Immune Activation

Highlights

• Interleukin-2 (IL-2) has emerged as a rapid, sensitive, and specific biomarker of gluten-induced T-cell activation in celiac disease (CeD).
• Acute immune activation occurs at gluten doses as low as 3 mg, which is significantly below the thresholds currently used for many international food-labeling standards.
• Patient-reported symptoms are unreliable indicators of gluten exposure at doses below 1000 mg, whereas IL-2 levels show a clear dose-dependent relationship.
• The eliciting dose (ED) values derived from recent RCTs provide a robust framework for defining safe exposure limits and improving clinical trial designs.

Background

Celiac disease (CeD) is a chronic immune-mediated enteropathy characterized by a permanent intolerance to gluten in genetically predisposed individuals (HLA-DQ2 or HLA-DQ8 positive). While the gluten-free diet (GFD) remains the cornerstone of management, absolute avoidance of gluten is virtually impossible due to cross-contamination and the ubiquitous nature of gluten in the food supply. This has led to the establishment of food-labeling standards, such as the widely adopted 20 parts per million (ppm) threshold, which assumes that trace amounts of gluten are clinically negligible. However, the precise biological threshold at which gluten triggers an immune response has remained elusive for decades. Traditional markers of disease activity, such as villous atrophy or serology (e.g., anti-tissue transglutaminase antibodies), lack the sensitivity to detect acute, low-dose exposures. Recent research has pivoted toward systemic cytokines, particularly Interleukin-2 (IL-2), which is released by gluten-specific CD4+ T cells shortly after gluten ingestion, offering a potential “gold standard” for monitoring acute immune activation.

Key Content

The Emergence of Interleukin-2 as a Primary Biomarker

Historically, assessing the impact of gluten exposure required prolonged challenges (weeks to months) followed by invasive duodenal biopsies to observe histological deterioration. In 2020 and 2021, research groups began to demonstrate that a single oral gluten challenge could induce a rapid spike in serum IL-2.

In a randomized, double-blind, 2-dose gluten challenge trial (PMID: 33130104), investigators compared 3 g and 10 g of gluten per day. While histological changes (villous height to crypt depth ratio) and gut-homing T cells only showed significant changes at the higher 10 g dose, plasma IL-2 levels increased significantly at both doses. This established IL-2 as the earliest and most sensitive marker of acute gluten exposure, responding within 2 to 6 hours of ingestion.

Quantifying the Gluten Threshold: The 2026 Adaptive Dose-Response Study

Building on this sensitivity, Daveson et al. (2026, PMID: 41903816) conducted a landmark randomized, double-blind, placebo-controlled adaptive dose-response trial. This study aimed specifically to identify the lowest gluten dose elicits a measurable immune response.

Fifty-one adults with treated CeD underwent challenges with doses ranging from 1 mg to 1000 mg. The primary endpoint was a ≥2-fold rise in serum IL-2 within 6 hours. The results revealed a striking dose-dependent relationship:

• 1000 mg and 610 mg: 83% of participants showed a significant IL-2 response.
• 90 mg: 36% of participants responded.
• 3 mg to 13 mg: 17% to 27% of participants showed immune activation.
• 1 mg to 2 mg: No significant IL-2 response compared to placebo.

Using interval-censored survival analysis, the study estimated the Eliciting Dose (ED) for the population. The ED50 (dose eliciting a response in 50% of the population) was 111 mg. More critically for food safety, the ED10 was 2.4 mg and the ED05 was 0.8 mg. These findings suggest that for a subset of the celiac population, the “safe” threshold may be significantly lower than the levels permitted under current labeling laws when cumulative daily intake is considered.

Symptoms vs. Biological Response

A critical finding across the synthesized literature is the dissociation between symptoms and immune activation. In the 2026 dose-response study, symptom scores increased after challenges but did not significantly differ from placebo at doses below 1000 mg. This suggests a significant “nocebo” effect or that low-level immune activation simply does not cross the threshold for symptomatic perception.

Furthermore, research published in Alimentary Pharmacology & Therapeutics (PMID: 31769533) identified that only specific symptoms—nausea and vomiting—correlate strongly with the magnitude of IL-2 release. IBS-like symptoms (bloating, flatulence, abdominal pain) were often present after sham challenges (placebo), indicating they are unreliable indicators of recent gluten exposure. This has profound implications for clinical practice, as patients may mistakenly attribute symptoms to gluten or, conversely, may be experiencing silent immune activation from trace exposures.

Differentiating Celiac Disease from Non-Celiac Gluten Sensitivity (NCGS)

One of the most valuable clinical applications of IL-2 monitoring is in differential diagnosis. Patients with self-reported gluten sensitivity often present on a GFD, making traditional celiac testing difficult. Studies (PMID: 32213060, PMID: 34797778) have shown that while gluten ingestion triggers a significant rise in IL-2, IL-8, and IL-10 in celiac patients, no such cytokine response occurs in individuals with NCGS. This “cytokine release assay” effectively identifies true T-cell mediated celiac disease and can help patients decide whether a strict, lifelong GFD is biologically necessary.

Translational Insights for Drug Development

The sensitivity of IL-2 is currently being leveraged in clinical trials for novel CeD therapies, such as Nexvax2 (a peptide-based immunotherapy). Early-phase trials (PMID: 31407810, PMID: 34093551) used IL-2 levels to monitor the induction of T-cell non-responsiveness. By measuring the reduction in gluten-stimulated cytokine release, researchers can assess a drug’s efficacy without the need for repeated, burdensome biopsies. The development of whole-blood cytokine release assays (CRA) further simplifies this process, allowing for immunomonitoring in large-scale, multi-center trials.

Expert Commentary

The shift toward IL-2 as a diagnostic and research tool represents a paradigm change in celiac disease management. The data from Daveson et al. provide the most rigorous evidence to date that our current food safety thresholds may need re-evaluation. While 20 ppm is generally considered safe for the majority, the fact that 10% of patients may respond to as little as 2.4 mg suggests that sensitive individuals may still experience chronic, low-level inflammation.

However, a crucial question remains: Does a transient spike in IL-2 without symptoms or immediate histological damage lead to long-term adverse health outcomes (e.g., osteoporosis, malignancy, or refractory disease)? Current guidelines (NCCN, WGO) still rely on mucosal healing as the primary therapeutic goal. Until longitudinal studies link acute IL-2 responses to long-term morbidity, IL-2 should be viewed as a highly sensitive indicator of exposure rather than a definitive proxy for disease progression.

Clinicians should also be wary of the variability in IL-2 responses. Not all celiac patients are “responders” in systemic assays, potentially due to variations in HLA type or the sequestration of T cells in the gut mucosa. Therefore, while a positive IL-2 test is highly specific for CeD, a negative test after a single low-dose challenge may not definitively rule out the disease.

Conclusion

Celiac disease research has entered an era of precision immunomonitoring. Interleukin-2 has proven to be an early, sensitive, and dose-dependent biomarker that far outperforms traditional symptom scores or histology for detecting acute gluten exposure. Current evidence indicates that immune activation occurs at milligram doses (ED10 = 2.4 mg), far below the 1000 mg typically required to elicit reliable symptoms. These findings provide a vital framework for future food-labeling regulations and the rational design of clinical trials. Future research must now determine the long-term clinical significance of these low-dose immune triggers to optimize the balance between strict gluten avoidance and patient quality of life.

References

• Daveson AJM, et al. A Randomized Double-Blind, Placebo-Controlled Dose-Response Study to Assess the Gluten Threshold Dose in Celiac Disease. Gastroenterology. 2026. PMID: 41903816.
• Croese J, et al. Plasma IL-2 and Symptoms Response after Acute Gluten Exposure in Subjects With Celiac Disease or Nonceliac Gluten Sensitivity. Am J Gastroenterol. 2022. PMID: 34797778.
• Sarna G, et al. Evaluating Responses to Gluten Challenge: A Randomized, Double-Blind, 2-Dose Gluten Challenge Trial. Gastroenterology. 2021. PMID: 33130104.
• Tye-Din JA, et al. Cytokine release after gluten ingestion differentiates coeliac disease from self-reported gluten sensitivity. United European Gastroenterol J. 2020. PMID: 32213060.
• Daveson AJM, et al. Masked bolus gluten challenge low in FODMAPs implicates nausea and vomiting as key symptoms associated with immune activation in treated coeliac disease. Aliment Pharmacol Ther. 2020. PMID: 31769533.