Mass spectrometry imaging has become one of the most powerful tools in modern biology because it can map hundreds of molecules directly within a tissue slice, revealing where lipids, metabolites, proteins and other biomolecules reside without labels or stains. Yet the technique has long been constrained by its spatial resolution. Conventional instruments raster a laser across a tissue section with a defined step size, and features smaller than that step blur together. Boosting resolution usually demands costly instrumentation such as specialized lasers, transmission-mode optics or next-generation ion optics, placing subcellular molecular imaging out of reach for many laboratories.

TEMI takes a different path. Instead of refining the instrument, the team enlarges the tissue itself. Drawing on principles from expansion microscopy, a technique introduced more than a decade ago, the researchers embed tissue in a water-rich hydrogel polymer network. When the gel swells, it carries the tissue along with it, spreading the molecules apart and effectively magnifying the sample before any mass spectrometry takes place. A laser raster that would have been too coarse for the original tissue becomes fine enough to resolve individual cells in the expanded version, yielding more than a 3.5-fold improvement in effective imaging resolution with standard equipment.

The critical challenge was chemistry. Traditional expansion protocols often rely on harsh denaturation conditions, including high heat and strong detergents, to homogenize tissue and allow gels to stretch uniformly. Those conditions would destroy the very molecules mass spectrometry aims to detect. The TEMI workflow solves this by using a re-embedding strategy that expands tissue under mild, harsh-condition-free conditions, preserving the chemical integrity of lipids, metabolites, N-glycans, peptides and proteins. The result is a sample that is both physically enlarged and chemically faithful to its original molecular composition.

The published protocol walks readers through every stage of the process. It begins with constructing a gelation chamber, then describes hydrogel-based tissue gelation and expansion, followed by cryosectioning of the expanded tissue-hydrogel composite. Because expanded samples are soft and hydrated, cutting them into thin sections requires careful handling, and the protocol provides the specific parameters that make reproducible sectioning possible. Detailed guidance covers matrix application, data acquisition and visualization pipelines, along with troubleshooting tips accumulated through the team’s extensive experimentation.

One of the most striking capabilities of TEMI is multiomics mapping on a single tissue section. The protocol describes a sequential workflow in which N-glycans are released in situ by treatment with the enzyme PNGase F, after which proteins are digested with trypsin and imaged, all following lipid and metabolite analysis on the same expanded section. This means a single slice of brain tissue can yield spatially resolved maps of multiple molecular classes, each anchored to the same anatomical context, an efficiency that conventional workflows struggle to match.

Quality control receives particular attention. The protocol includes a dedicated workflow for measuring deformation maps and expansion factors, which quantify how uniformly the gel has expanded. Uneven expansion would distort molecular maps, so the researchers provide computational tools, released through a public code repository, that quantify tissue expansion non-uniformity. They also demonstrate that analyte delocalization during sample preparation is minimal: lipid and small-metabolite signals were detected exclusively in tissue regions, with no corresponding signals in adjacent blank hydrogel areas, confirming that molecules stay where they belong during the swelling process.

The demonstration experiments showcase the method’s power on the mouse cerebellum, a tissue with exquisitely organized layers of cells. Comparing an unexpanded control cerebellum imaged with a 50-micrometer laser raster against a double-embedded, expanded sample at the same step size reveals a dramatic difference in molecular detail. Pushing further, the team performed TEMI after three cycles of gel embedding and expansion with a 10-micrometer raster step, resolving biomolecular heterogeneity that remains invisible in unexpanded tissue. The protocol also demonstrates mapping of small metabolites, N-glycans and proteins across cerebellar structures, illustrating the breadth of the multiomics capability.

The work builds on the team’s primary research paper published in Nature Methods, which introduced TEMI and established its foundational performance, and on a rich history of expansion microscopy methods developed by collaborators at the Howard Hughes Medical Institute’s Janelia Research Campus, including protein-retention expansion microscopy and ten-fold robust expansion. Raw datasets from the protocol’s figures are publicly available in the MassIVE repository, and the deformation-measurement code is hosted on GitHub, lowering barriers for laboratories that want to adopt or adapt the approach.

The implications extend across basic biology and medicine. Single-cell spatial resolution for untargeted molecular imaging could illuminate how metabolic gradients shape tissue function, how lipid compositions vary between neighboring cells in the nervous system, and how disease states such as cancer or neurodegeneration alter molecular architecture at scales previously accessible only to antibody-based imaging. Because TEMI requires no instrument modifications, it promises broad accessibility: laboratories with standard mass spectrometry imaging systems can now reach a resolution regime once reserved for a handful of specialized facilities. The protocol’s authors, spanning the University of Wisconsin-Madison and HHMI Janelia, and supported in part by the National Institutes of Health, position the method as a practical bridge between the spatial-omics revolution and the everyday mass spectrometry lab, inviting a wide research community to stretch its view of tissue, quite literally, into sharper focus.

Subject of Research: Tissue expansion combined with mass spectrometry imaging for high-spatial-resolution multiomics molecular mapping

Article Title: Tissue expansion mass spectrometry imaging (TEMI) for high-spatial-resolution multiomics molecular mapping

Article References: Tissue expansion mass spectrometry imaging (TEMI) for high-spatial-resolution multiomics molecular mapping. (n.d.). https://doi.org/10.1038/s41596-026-01427-w

Image Credits: AI Generated

DOI: 10.1038/s41596-026-01427-w

Keywords: mass spectrometry imaging, tissue expansion, TEMI, spatial omics, single-cell imaging, lipidomics, metabolomics, N-glycans, proteomics, hydrogel expansion, Nature Protocols, multiomics

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