Blood Sugar Chains on Antibodies Forecast Dangerous Reactions to Allergy Shots

Allergen-specific immunotherapy is the only treatment that actually changes the course of allergic disease rather than merely masking its symptoms. For patients with allergic rhinitis and allergic asthma, repeated injections of gradually increasing doses of allergen can retrain the immune system and build lasting tolerance. Yet the therapy carries a persistent clinical dilemma: some patients sail through treatment, while others experience local swelling, systemic reactions, or full anaphylaxis, and clinicians currently have no reliable way to know in advance who will tolerate the treatment and who will not. A new study published in Clinical Proteomics suggests that the answer may be written in the sugar molecules attached to a single class of antibodies circulating in the blood.

The research, led by Ran Zhao, Na Dong, and Xiaoyan Dong of Shanghai Children’s Hospital at Shanghai Jiao Tong University, together with Weilong Zhang and Shifang Ren of Fudan University’s NHC Key Laboratory of Glycoconjugates Research, examined how immunoglobulin G glycosylation changes during the course of subcutaneous allergen immunotherapy. Immunoglobulin G, the most abundant antibody in human plasma, carries a conserved N-glycan at a specific asparagine residue in its Fc region. This glycan is not decorative. Its composition, including the number of terminal galactose and sialic acid residues and the presence of a bisecting N-acetylglucosamine, directly modulates the antibody’s ability to engage Fc gamma receptors on immune cells and thereby determines whether IgG exerts pro-inflammatory or anti-inflammatory effects.

Decades of work have established that IgG glycosylation shifts measurably in inflammatory conditions. Reduced galactosylation and sialylation are hallmarks of active rheumatoid arthritis, and intravenous immunoglobulin preparations owe part of their anti-inflammatory activity to a small sialylated fraction. Because successful allergen immunotherapy is thought to depend on regulatory B cells producing IgG4 and on interleukin-10-driven tolerance mechanisms, the researchers reasoned that the glycan profile of plasma IgG might track the immunological state of patients undergoing the therapy, and might even flag those at risk of adverse reactions before treatment begins.

To test this, the team enrolled 37 patients with allergic asthma or allergic rhinitis who were beginning subcutaneous immunotherapy, largely against house dust mite allergens such as Dermatophagoides pteronyssinus. Of these, 26 patients were followed longitudinally at three time points: before treatment, at the initiation of the maintenance phase, and after more than six months of maintenance injections. Plasma samples were collected at each visit, IgG was purified, and its N-linked glycans were released and profiled by ultra-performance liquid chromatography, a high-resolution technique that separates glycans into discrete chromatographic peaks, each corresponding to a defined glycan structure that can be quantified as a percentage of total glycan signal.

The longitudinal data revealed a coherent remodeling of the IgG glycome as tolerance developed. Total galactosylation and sialylation of IgG glycans rose gradually across the treatment course, while the proportion of bisecting glycans, structures bearing a bisecting N-acetylglucosamine added by the enzyme GnT-III, declined. This pattern is consistent with a shift toward the anti-inflammatory, sialylated IgG species associated with immune regulation, and it provides a mechanistic readout of the tolerance process that clinicians have previously had to infer indirectly from symptom scores and medication use.

The more striking result emerged when the researchers compared baseline samples from patients who later experienced adverse reactions with those who tolerated the therapy. Patients destined to react showed significantly elevated levels of the glycan peak designated GP6, reduced levels of peaks GP18 and GP23, lower overall galactosylation and sialylation, and increased bisecting glycans before receiving any treatment. In other words, the pretreatment glycan signature of reactive patients resembled a pro-inflammatory state, with IgG skewed toward agalactosylated, asialylated, and bisected structures known to enhance antibody-dependent effector functions through activating Fc gamma receptors.

To translate these differences into a clinically usable predictor, the team performed receiver operating characteristic analysis, a standard method for evaluating how well a biomarker discriminates between two groups across all possible thresholds. A combined model built from multiple glycan features achieved an area under the curve of 0.863 for predicting adverse reactions, a level of discrimination that, if validated, would substantially outperform the clinical history and skin testing alone that currently guide risk assessment. Because the measurement requires only a small plasma sample drawn before therapy starts, the authors describe the approach as minimally invasive and mechanism-based, offering a route to pretreatment risk stratification that could allow clinicians to adjust dosing schedules, intensify monitoring, or select alternative management for high-risk individuals.

The implications extend beyond the allergy clinic. Glycosylation is increasingly recognized as a sensitive barometer of immune status, and this study adds allergen immunotherapy to the growing list of contexts in which IgG N-glycan profiling carries genuine predictive power. The work also connects to a broader mechanistic picture: regulatory T cells and regulatory B cells, interleukin-10 signaling, and the IgG4 class-switching that characterizes successful immunotherapy all intersect with the glycan machinery of antibody-producing cells. A glycan biomarker therefore does not merely correlate with outcomes; it plausibly reflects the underlying immunological shift from a Th2-dominated allergic phenotype toward tolerance.

The authors are careful to note the limitations of the study. The cohort of 37 patients, drawn from a single pediatric hospital, is modest in size, and the findings require validation in larger, multicenter populations before glycan profiling can enter routine practice. The published version remains subject to final editorial updates, and the researchers emphasize that further work is needed to standardize the chromatographic assay, define cut-off values, and test whether the same signatures apply to adults, to other allergen extracts, and to sublingual as well as subcutaneous routes of administration. Still, the combination of a strong longitudinal signal, a clear baseline distinction between tolerant and reactive patients, and a respectable area under the curve makes this one of the more compelling biomarker candidates to emerge in the allergy field in recent years.

If multicenter validation confirms the result, the practical consequences could be significant. Allergen immunotherapy is underused relative to its disease-modifying potential, partly because of safety concerns and the burden of monitoring patients through a months-long buildup phase. A simple blood test that identifies patients at elevated risk of reactions before the first injection would allow the therapy to be offered more confidently to suitable candidates and tailored more cautiously to those at risk. It would also open a window on the biology of tolerance itself, letting researchers watch, in molecular detail, as the immune system learns to accept what it once attacked. For a field long guided by trial and error, the sugars on a single antibody may finally provide the objective compass that clinicians have been missing.

Subject of Research: IgG N-glycan profiling as a predictive biomarker for adverse reactions in allergen-specific immunotherapy

Article Title: Plasma IgG glycan dynamics predict adverse reactions in allergen immunotherapy

Article References: Plasma IgG glycan dynamics predict adverse reactions in allergen immunotherapy. (n.d.). https://doi.org/10.1186/s12014-026-09627-y

Image Credits: AI Generated

DOI: 10.1186/s12014-026-09627-y

Keywords: allergen immunotherapy, IgG glycosylation, N-glycans, allergic asthma, allergic rhinitis, biomarkers, adverse reactions, immune tolerance, Clinical Proteomics, ultra-performance liquid chromatography, ROC analysis, glycomics