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.