BackgroundImmunoglobulin overproduction was observed in type 2 chronic rhinosinusitis with nasal polyps (CRSwNP). Endoplasmic reticulum (ER) stress is linked to aggregation in various inflammatory diseases, yet its presence and extent in nasal polyps remain to be elucidated.ObjectiveTo assess the impact of B-cell ER stress on local immunoglobulin production in CRSwNP and investigate its correlation with disease severity.MethodsSingle-cell mapped transcriptional profiles at cellular resolution. Electron microscopy revealed ultrastructural features, complemented by immunohistochemistry/immunofluorescence mapping marker localisation. Western blotting quantified protein expression, with QuantiGene Plex and Luminex enabling multiplex cytokine analysis. Bulk RNA sequencing and targeted protein expression validation in ex vivo experiments confirmed critical findings.ResultsHSPA5 and HSP90B1 were found to be two major elevated ER stress markers in type 2 CRSwNP, compared to the control nasal tissue, and their expression correlated with the expression of IGHE and type 2 inflammatory markers. In CRSwNP, the ER stress signature score and increased marker expression predominantly originated from B and plasma cells. Electron microscopy revealed dilated ER and enlarged lumen in sorted B cells from nasal polyps. MZB1 exhibited co-localisation with plasma cells and mature B cells. Immunofluorescence staining demonstrated that MZB1 co-localised with HSPA5 and HSP90B1. In vitro, stimulation with MZB1 upregulated mRNA expression of ER stress markers and IgE. Increased IGHE expression was detected in response to ER stress induced in vitro. Finally, anti-IgE treatment inhibited the expression of ER stress-related genes.ConclusionER stress markers were significantly upregulated in CRSwNP. Specifically, ER stress levels were significantly elevated in B cells of CRSwNP compared to controls. In type 2 CRSwNP, B-cell ER stress may play a role in promoting local IgE production.