IgG4-related disease is characterized by tumor-like infiltrates rich in IgG4-positive plasma cells, storiform fibrosis, and elevated serum IgG4 concentrations. Patients frequently present with IgG4-related autoimmune pancreatitis, in which the pancreas becomes swollen and rigid, or with Mikulicz disease, marked by painless enlargement of the salivary and lacrimal glands. Although the pathology is well described, the initiating events have been poorly understood. Proposed mechanisms range from autoantibody production to aberrant cytotoxic T lymphocyte activity, yet the triggers that set the immune system on its characteristic type 2 trajectory remain uncertain. Intriguingly, trypsin has been used for decades as an adjunctive therapy for chronic inflammatory and autoimmune conditions, a clinical tradition that made the enzyme’s gene an unexpected but thought-provoking candidate when variants began appearing in the sequencing data.

The research team, led by investigators at the First Affiliated Hospital of Fujian Medical University, applied whole-exome sequencing to affected tissue samples from three patients: two with IgG4-related autoimmune pancreatitis and one with Mikulicz disease. This approach reads the protein-coding regions of the genome in exhaustive detail, allowing rare variants to be detected directly in diseased tissue. Among the mutations surfaced in the analysis, the p.Lys70Asn and p.Phe73Leu changes stood out because both alter amino acids within trypsinogen, potentially modifying the protein’s folding, activation, or stability. Because these variants were identified in lesion tissue rather than blood alone, they may reflect changes present in the affected organs themselves, raising the possibility that altered trypsinogen biology contributes locally to disease development.

Equally important was what the researchers observed when they examined the cellular composition of the affected tissues. Histological and transcriptional analysis revealed activation of M2 macrophages, the anti-inflammatory, tissue-repair-oriented members of the macrophage family. Macrophages are not a uniform population; classically activated M1 macrophages drive antimicrobial inflammation, while alternatively activated M2 macrophages promote wound healing, fibrosis, and type 2 immune responses through cytokines such as transforming growth factor beta and interleukins. In IgG4-related disease, an overabundance of M2 activity could explain two hallmark features at once: the exuberant fibrosis that hardens affected organs and the Th2-skewed immune environment that drives B cells to class-switch toward IgG4 production. Prior work by other groups had already implicated interleukin-33 produced by M2 macrophages in the Th2 reaction of IgG4-related disease, lending plausibility to the new observations.

To place these findings in a higher-resolution context, the team integrated single-cell RNA sequencing datasets with spatial transcriptomic analysis of pancreatic tissue from the mutation-positive cases. Single-cell RNA sequencing dissects a tissue into its constituent cell types and profiles gene expression in each one, while spatial transcriptomics preserves the geographic information, revealing which cell populations sit next to which structures within the intact organ. Combining the two techniques allowed the researchers not only to catalog the immune cells infiltrating the pancreas but also to map their physical relationships. This spatial map showed that M2 macrophage-derived molecules, including TGF-beta, occupy positions consistent with a role in promoting type 2 immune responses within the lesion microenvironment, effectively linking the cellular census to the architectural reality of the diseased tissue.

The mechanistic picture that emerges is a plausible multi-step model. Variants such as p.Lys70Asn and p.Phe73Leu may perturb trypsinogen handling in pancreatic or glandular tissue, creating local stress or altered proteolytic signaling. That perturbation could favor recruitment and polarization of macrophages toward the M2 state. Once established, M2 macrophages would secrete TGF-beta and other mediators that sculpt the immune milieu toward Th2 dominance, encouraging IgG4 class-switching in B cells and the fibrotic remodeling that characterizes the disease. The authors conclude that these novel PRSS1 variants may contribute to the pathogenesis of IgG4-related disease by activating type 2 immune responses, a formulation that positions trypsinogen genetics upstream of the immunological cascade rather than as a bystander.

The study carries several caveats worth noting. The sequencing cohort comprised only three patients, a sample size dictated by the rarity of the disease and the difficulty of obtaining affected tissue, so the prevalence of the PRSS1 variants in the broader IgG4-related disease population remains unknown. The evidence connecting the variants to macrophage polarization is associative, drawn from tissue analysis and transcriptomic correlation rather than from direct functional experiments demonstrating that the mutant trypsinogen induces M2 skewing. Future work will need to reproduce the findings in larger cohorts, test the variants in cellular and animal models, and determine whether the mutations are inherited, somatic, or arise through other mechanisms. The data underlying the study are available from the corresponding author upon reasonable request, and the work was approved by the Medical Ethics Committee of the First Affiliated Hospital of Fujian Medical University with written informed consent from all participants.

Even with those limitations, the implications are considerable. If PRSS1 variants indeed seed the type 2 immune environment of IgG4-related disease, they could serve as biomarkers for identifying patients at risk or for classifying disease subtypes. More ambitiously, they point toward interventions that target the trypsinogen-macrophage axis, whether through modulating protease activity, dampening M2 polarization, or intercepting TGF-beta signaling. The findings also resonate with a long clinical curiosity: trypsin’s historical use as an anti-inflammatory therapeutic. Understanding how trypsinogen variants behave in disease tissue may eventually clarify when protease-based approaches help and when they might be counterproductive.

For a disease that has long defied simple explanation, the Fujian team’s work adds a concrete genetic and cellular thread to the story. By uniting whole-exome sequencing, single-cell transcriptomics, and spatial mapping in the same patients, the study demonstrates how modern multi-omics tools can convert rare clinical specimens into mechanistic hypotheses. The discovery that trypsinogen isoforms and variants may promote type 2 immune responses in IgG4-related disease does not close the case on this enigmatic condition, but it opens a well-defined line of investigation, one that traces the path from a DNA sequence change to an immune microenvironment and, ultimately, to the fibrotic organ damage that patients experience.

Subject of Research: Novel PRSS1 trypsinogen gene variants and their role in type 2 immune responses in IgG4-related disease

Article Title: PRSS1 isoforms promote type 2 immune responses in IgG4-related disease

Article References: PRSS1 isoforms promote type 2 immune responses in IgG4-related disease. (n.d.). https://doi.org/10.1038/s41435-026-00412-3

Image Credits: AI Generated

DOI: 10.1038/s41435-026-00412-3

Keywords: IgG4-related disease, PRSS1, trypsinogen, M2 macrophages, type 2 immune response, autoimmune pancreatitis, Mikulicz disease, whole-exome sequencing, single-cell RNA sequencing, spatial transcriptomics, TGF-beta, immunogenetics