Synthetic coincidence of BCR-NF-κB and IL-4Rα-STAT6 signaling constitutes a master checkpoint for functional IgE class switch recombination.

BACKGROUND: Aberrant immunoglobulin E (IgE) class-switch recombination (CSR) underlies globally prevalent type 2 allergic disorders affecting hundreds of millions of people worldwide. Under homeostatic conditions, IgE production is tightly restrained, whereas IgG4 and IgA CSR readily proceed; the molecular mechanisms enforcing this restriction remain incompletely defined. Both BCR-NF-κB and IL-4Rα-STAT6 contribute to IgE-related transcriptional programming, yet it remains unclear whether isolated or concurrent pathway activity drives functional IgE CSR. OBJECTIVE: To characterize the molecular threshold for productive IgE CSR under defined experimental conditions and test a signaling-coincidence model, together with exploring potential correlative clinical observations and pre-clinical therapeutic opportunities. METHODS: Primary naive mouse B cells and human peripheral-blood-derived naive B cells were cultured under constant CD40L co-stimulation with three experimental conditions: isolated BCR activation, isolated IL-4Rα activation, or dual-pathway co-activation. Assays included qPCR, ATAC-seq, ChIP-qPCR, proximity ligation assay (PLA), sequential re-ChIP and flow cytometry to quantify germline ε (GLT-ε) transcription, Sε chromatin accessibility, transcription-factor interactions and isotype-switching efficiency. B-cell-specific conditional-knockout mouse lines were used for in-vivo experimental testing. Nasal inferior-turbinate biopsies from patients with allergic rhinitis and matched healthy volunteers were analyzed for correlative immune profiling. Three pharmacological interventions targeting distinct nodes of this dual-signal axis were assessed. RESULTS: Under fixed CD40L co-stimulation, isolated BCR or isolated IL-4Rα stimulation supported IgG4/IgA switching but yielded minimal GLT-ε transcription, closed Sε-region chromatin and negligible functional IgE secretion in mouse and human naive B cells. Concurrent activation of both pathways triggered physical interaction and genomic co-occupancy of NF-κB and STAT6 at the Sε locus, recruiting CBP/p300 to deposit permissive histone modifications, remodeling chromatin and enabling robust AID loading to support IgE CSR. In human nasal mucosa, coincident B-cell NF-κB-STAT6 activity correlated with elevated local IgE among allergic rhinitis patients, whereas signal decoupling was observed in healthy control tissue. Pharmacological targeting of IL-4Rα, circulating free IgE or the NF-κB-STAT6 protein-protein interface reduced IgE production without abrogating IgG/IgA generation within our assay systems. CONCLUSION: Our experimental data support a coincidence-gated model for IgE CSR in the tested in-vitro and pre-clinical mouse systems. Concurrent BCR-NF-κB and IL-4Rα-STAT6 pathway inputs appear strongly required for robust productive IgE rearrangement under these experimental settings. This signaling-coincidence framework offers mechanistic insights into physiological constraints limiting IgE responses. Whether these observations translate into clinical utility warrants further independent investigation.