D1.41 - B cell responses to alarmins in type 2 inflammation

Type 2 inflammation is shaped by cytokines and epithelial alarmins that coordinate immune responses in barrier tissues. While B cells are traditionally viewed as antibody-producing cells, increasing evidence suggests that they actively integrate cytokine- and receptor-mediated signals to adopt distinct effector programs. How type 2 cytokines and alarmins regulate human B cell function remains incompletely understood.

Human B cells were isolated from peripheral blood and tonsillar tissue of healthy donors. To assess induction of alarmin receptor expression, B cells were stimulated in vitro with combinations of CD40L, IL-4, CpG, and B cell receptor (BCR) engagement, and receptor subunit expression was quantified by quantitative PCR. In separate experiments assessing functional responses, B cells were stimulated with CD40L alone or combined with IL-4, IL-25, and BCR engagement. B cell phenotypes and effector responses were analyzed by flow cytometry, ELISA, and Olink proximity extension proteomics.

Stimulation with CD40L and IL-4, with or without CpG, induced a marked shift in B cell activation and robust upregulation of type 2 cytokine- and alarmin-associated receptors, including IL-4Rα, IL-13Rα1, IL-17RB, and IL-21Rα, particularly in the presence of CD40L. In contrast, TSLP and IL-33 receptor subunits were not induced under any condition tested, including those incorporating CpG or BCR engagement. Accordingly, functional analyses focused on IL-25 as the only alarmin for which B cells were rendered responsive.

IL-25 alone had minimal effects on B cell cytokine production and proteomic profiles, indicating that alarmin signaling does not act as a primary activation signal. However, IL-25 selectively modulated CD40L- and IL-4-primed B cells, enhancing IL-10 production and IgG4 secretion. Engagement of the BCR introduced a distinct inflammatory activation axis that was amplified by IL-4 and associated with increased IFN-γ expression. Notably, addition of IL-25 attenuated this inflammatory signature, while preserving or enhancing regulatory and interaction-associated outputs, including CXCL12, CCL23, FASLG, and TRAIL. These effects were consistent across donors and reflected context-dependent reprogramming of B cell effector functions.

These findings demonstrate that IL-4 selectively licenses human B cells for IL-25 responsiveness, whereas expression of TSLP and IL-33 receptor subunits remains unchanged. IL-25 acts as a context-dependent modulator, fine-tuning B cell effector and interaction programs under type 2 inflammatory conditions.