IgG4⁺ plasma cell enrichment and {lambda}-chain-biased BCR remodeling drive low-grade autoimmunity in chronic obstructive pulmonary disease

Background: This study aimed to elucidate B cell subset pathology in COPD, a poorly characterized area, with a focus on its similarities to and differences from classical autoimmune disorders. Methods: Single-cell RNA-sequencing (scRNA-seq) data from COPD and autoimmune diseases were obtained from the Gene Expression Omnibus (GEO) for comparative analyses of B cell subsets and functions via differentially expressed genes (DEGs), KEGG, protein-protein interaction (PPI), and cell-cell communication analyses. Serum IgG4 was measured by ELISA and correlated with clinical parameters. Peripheral blood B cells were sorted by flow cytometry for single-cell B cell receptor (BCR) sequencing. A v-Abl-Bcl2 pro-B cell line was stimulated with cigarette smoke extract (CSE) to assess abnormal development in vitro. Results: In lung tissue, IgG4 plasma cells were enriched and expressed BCR activation and inflammatory genes and TNF-NF-kB-MAPK pathways. Serum IgG4 concentrations correlated negatively with pre- and post-bronchodilator FEV1-FVC. B cells interacted with monocytes, macrophages, fibroblasts, and endothelial cells via IL-1B-IL-6, integrin, and chemokine signaling, contributing to chronic inflammation and remodeling. In peripheral blood, transitional T1 B cells were increased, accompanied by lambda-chain enrichment and increased IGLV1-47 usage, as well as enrichment of autoimmune pathways. In the bone marrow, the numbers of pre-B I cells were increased while those of small pre-B III cells were reduced, with altered expression of BCR development genes. CSE stimulation of the pro-B cell line reduced lambda expression in a concentration-dependent manner. Conclusions: The autoimmune abnormalities in COPD appear more restricted, although IgG4 antibody generation may contribute to immune-mediated lung damage.