The finding is significant because IgE sits at the very center of the allergic cascade. Allergen-specific IgE is produced exclusively by B cells, and upon re-exposure to an allergen such as house dust mite, these antibodies arm mast cells and basophils, triggering their degranulation and the clinical symptoms of asthma. At the same time, T helper 2 cells recruited to the airways secrete IL-4, IL-5 and IL-13, cytokines that promote local IgE production, eosinophil accumulation, airway hyperresponsiveness and mucus hypersecretion. While the extracellular signals that push B cells toward IgE have been studied extensively, the intrinsic molecular machinery inside B cells that governs this process has remained poorly defined, which is precisely the gap the new work addresses.

The researchers began by asking whether Ssu72 responds to the signals that activate B cells during allergic reactions. In cultured mouse B cells, Ssu72 protein and mRNA levels rose markedly after stimulation with anti-CD40, an antibody that mimics the T cell help B cells receive through CD40 ligation, as well as after combined anti-IgM and anti-CD40 stimulation and exposure to the T helper 2 cytokine IL-4. Crucially, the pattern held in vivo: in a low-dose house dust mite model of allergic asthma, B cells from the spleens of asthmatic mice showed significantly elevated Ssu72 compared with controls, and immunofluorescence imaging revealed heightened Ssu72 expression in B220-positive B cells infiltrating the inflamed lungs. The enzyme, in other words, is switched on exactly where and when the allergic response is being built.

To test whether this upregulation matters functionally, the team generated mice lacking Ssu72 only in B cells by crossing Ssu72-floxed animals with CD19-Cre mice, producing what they call Ssu72-BKO mice. Importantly, baseline B cell development appeared largely intact: total splenic B cell numbers were comparable to wild-type littermates, and with careful gating the major follicular, transitional and marginal zone subsets were unchanged. The knockout mice also mounted normal antigen-specific IgM and IgG responses after immunization with T cell-dependent and T cell-independent antigens, formed normal germinal centers and generated normal plasma cell populations. Ssu72, it seems, is dispensable for general antibody immunity but becomes critical in the specific context of allergic, T helper 2-driven inflammation.

That context-dependence showed itself clearly in the asthma model. After sensitization and challenge with house dust mite extract, Ssu72-BKO mice had visibly less peribronchial and perivascular inflammation on histology, lower inflammation scores, and significantly fewer total cells, eosinophils, T cells and B cells in bronchoalveolar lavage fluid. Immunohistochemistry for B220 and eosinophil cationic protein confirmed reduced B cell and eosinophil infiltration in lung tissue. Most strikingly, serum levels of total and house dust mite-specific IgE and IgG1 were substantially lower in the knockout animals, while HDM-specific IgM, IgG2b and IgG3 were unaffected, indicating that B cell Ssu72 preferentially supports the IgG1 and IgE arms of the allergic antibody response.

Flow cytometry of the mediastinal lymph nodes revealed why. Class switching to IgG1 and IgE normally occurs in germinal centers with help from T follicular helper cells, and in Ssu72-BKO mice both the percentage and number of IgG1-positive B cells, germinal center B cells and T follicular helper cells were significantly reduced after asthma induction. The defect was also cell-intrinsic: when purified B cells from knockout and wild-type mice were stimulated in vitro with LPS plus IL-4, the Ssu72-deficient cells showed markedly fewer IgG1-positive cells at days three and six, fewer intracellular IgE-positive cells at day six, and lower secreted IgG1 and IgE, while IgM production was unaffected. The knockout B cells also proliferated less, expressed less Ki67, survived less well by Annexin V and propidium iodide staining, and showed blunted early activation markers CD69 and CD86.

The study also uncovered a second, mechanistically distinct route by which Ssu72 shapes IgE: the regulation of CD23, the low-affinity IgE receptor. Membrane-bound CD23 on B cells normally restrains IgE synthesis, whereas its cleaved soluble form, sCD23, enhances it. Ssu72-BKO mice produced significantly less sCD23 during house dust mite asthma while retaining higher levels of membrane CD23 on their lymph node B cells. The team traced this to reduced induction of ADAM10, the established sheddase that clips CD23 from the cell surface, and reduced expression of MMP9, a matrix metalloproteinase previously implicated in LPS-driven CD23 cleavage. Consistent with a conserved mechanism, an analysis of public RNA sequencing data from activated human B cells revealed a positive correlation between Ssu72 and MMP9 expression, suggesting the pathway may operate in human allergy as well.

Delving deeper into signaling, the researchers found that Ssu72-deficient B cells had reduced phosphorylation of S6K and S6, canonical readouts of mTORC1 activity, alongside sharply increased phosphorylation of AMPKα at Thr172, the activating modification of the cellular energy sensor AMPK. Because AMPK negatively regulates mTORC1, and mTORC1 drives the protein synthesis and anabolic growth that class-switched B cells need to proliferate and secrete antibody, this imbalance offers a coherent explanation for the defective IgG1 and IgE responses. Co-immunoprecipitation experiments in transfected HEK293T cells and in the human Ramos B cell line demonstrated a physical interaction between Ssu72 and AMPKα, raising the possibility that Ssu72 directly dephosphorylates AMPKα, although the authors note that direct phosphatase assays and catalytically inactive Ssu72 mutants will be needed to confirm AMPKα as a true substrate.

Perhaps the most clinically suggestive result came from adoptive transfer experiments. When B cells from wild-type or Ssu72-deficient donors were transferred into B cell-deficient μMT mice that had already been sensitized to house dust mite, and the recipients were then challenged, the mice receiving Ssu72-deficient B cells developed less lung inflammation, fewer airway eosinophils, T cells and B cells, and lower serum IgE. This shows that Ssu72 matters not only during the sensitization phase, when IgE-switched B cells are generated, but also during the effector phase, when re-exposure to allergen triggers disease. The knockout B cells additionally displayed reduced MHC class II upregulation in lymph nodes and lungs, and the mice showed fewer IL-4- and IL-13-producing CD4-positive T cells in both compartments, along with lower IL-4 in bronchoalveolar lavage fluid and serum, implying that Ssu72-expressing B cells help sustain the T helper 2 dialogue through antigen presentation.

Taken together, the study positions Ssu72 as a context-dependent, B cell-intrinsic checkpoint that licenses class switching to IgG1 and IgE, promotes CD23 shedding through ADAM10 and MMP9, and tunes the AMPK-mTORC1 metabolic axis. Because general humoral immunity was preserved in the knockout mice, the authors argue that selectively targeting Ssu72 in B cells could dampen allergic airway inflammation without broadly compromising the antibody defenses a patient needs against infection. Much remains to be worked out, including how Ssu72 controls ADAM10 and MMP9 expression and how the AMPK and CD23-shedding pathways intersect. But for a disease in which IgE remains a prime therapeutic target, an intracellular enzyme that quietly orchestrates its production offers an enticing new lead, and one that the field will now be eager to pursue from mouse airways toward human clinics.

Subject of Research: The role of the B cell-intrinsic phosphatase Ssu72 in regulating IgE production and allergic airway inflammation

Article Title: B cell-intrinsic Ssu72 phosphatase is a key regulator of allergic asthma

Article References: Koo, S.-Y., Wang, N., Kim, M.-H., Lee, S., Kim, T. J., & Lee, C.-W. (2026). B cell-intrinsic Ssu72 phosphatase is a key regulator of allergic asthma. Experimental & Molecular Medicine. https://doi.org/10.1038/s12276-026-01859-0

Image Credits: AI Generated

DOI: 10.1038/s12276-026-01859-0

Keywords: Ssu72 phosphatase, B cells, allergic asthma, IgE, class switch recombination, CD23 shedding, ADAM10, MMP9, AMPK, mTORC1, T helper 2 cytokines, house dust mite