Background:
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, accumulating evidence suggests that they actively integrate cytokine- and receptor-mediated signals to adopt distinct effector programs. How type 2 cytokines and alarmins interact to regulate human B cell function remains incompletely understood.
Methods:
Human B cells were isolated from peripheral blood and tonsillar tissue of healthy donors and stimulated in vitro using CD40L as a baseline activation, either alone or in combination with IL-4, IL-25, CpG, and B cell receptor (BCR) engagement. Expression of type II cytokine subunits in B cells was assessed by quantitative PCR, while B cell phenotypes and effector functions were evaluated using flow cytometry, ELISA, and Olink proximity extension proteomics.
Results:
Co-stimulation with CD40L and IL-4, with or without CpG, induced a pronounced shift in B cell activation, marked by broad changes in cytokine, chemokine, and co-stimulatory molecule expression, as well as upregulation of type 2 cytokine- and alarmin-associated receptors, including IL4Rα, IL13Rα1, IL17RB, and IL21Rα.Subunits of the TSLP and IL-33 receptors were also assessed but did not show upregulation under any condition. In contrast, CD40L alone induced only modest activation, and IL-25 without IL-4 had minimal effects, indicating that alarmin signaling does not serve as a primary B cell activator. Notably, IL-4-dependent upregulation of IL-17RB suggests that a type 2 cytokine environment licenses B cells for IL-25 responsiveness. In this context, IL-25 selectively modulated CD40L- and IL-4-primed B cells, enhancing IL-10 production and IgG4 secretion, indicative of a regulatory phenotype. Engagement of the B cell receptor (BCR) in CD40L-stimulated cultures introduced a distinct inflammatory axis, amplified by IL-4 and associated with increased IFN-γ expression. Addition of IL-25 to IL-4- and BCR-stimulated B cells attenuated this inflammatory signature while preserving regulatory outputs, including increased expression of chemokines (CXCL12, CCL23) and apoptosis-inducing ligands (FASLG, TRAIL). These donor-consistent effects reflect context-dependent reprogramming of B cell effector functions, demonstrating that IL-25/IL-17RB signaling fine-tunes B cell responses under type 2 cytokine-dominated conditions.
Conclusion:
These findings demonstrate that IL-4 selectively licenses human B cells for IL-25 responsiveness, whereas expression of TSLPR and IL-33 receptor subunits remained unchanged. IL-25 acts as a context-dependent modulator, fine-tuning B cell effector and interaction programs under type 2 conditions.