[Comprehensive analysis of the structural phenotypes and functional characteristics of B cells in oral lichen planus and oral lichenoid lesions through single-cell and spatial transcriptomics].

<b>Objective:</b> Comprehensive characterization of B-cell phenotypes and spatial distribution in oral lichen planus (OLP) and related oral lichenoid lesions (OLL)(OLP/OLL), with an emphasis on transcriptomic profiling and functional analysis, to uncover the epigenetic mechanisms underlying B cell-mediated immune regulation within the oral mucosal microenvironment. <b>Methods:</b> Single-cell RNA sequencing raw data were sourced from the GSE211630 database, encompassing samples from 2 cases of erosive OLP (EOLP), 3 cases of non-erosive OLP (NEOLP) and 1 healthy control (NORMAL). Following stringent quality control, the data underwent normalization, selection of highly variable genes and batch effect correction. Subsequent analyses included dimensionality reduction and unsupervised clustering to identify distinct cell populations. This study collected pathological specimens from 3 OLP/OLL patients and 3 healthy controls who were treated at the Department of Oral Medicine, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine from January 2021 to December 2023. Using 10X Genomics Visium HD spatial transcriptomics technology, tissue sections were processed through dewaxing, staining and histological imaging, enabling the reconstruction of nucleic acid structures and the capture of gene expression profiles. Data analysis included quality assessment, gene quantification, normalization, dimensionality reduction and clustering. Furthermore, cell type deconvolution was performed using the robust cell type decomposition algorithm, integrating single-cell transcriptomic data to accurately predict and spatially resolve cell type distributions within the tissue microenvironment. <b>Results:</b> After integrating single-cell data from EOLP, NEOLP and NORMAL, cells were classified into seven major categories: B/plasma cells, endothelial cells, epithelial cells, fibroblasts, myeloid cells, smooth muscle cells and T/natural killer cells. The proportion of B/plasma cells varied significantly among the three groups, accounting for 10.7% (1 693/15 815), 3.8% (833/21 653) and 0.4% (47/11 556) of the total cells respectively. Further clustering analysis of B/plasma cells identified four distinct subpopulations: naive B cells, activated B cells, memory B cells and plasma cells. In the EOLP group, these subpopulations constituted 25.9% (348/1 344), 45.9% (617/1 344), 3.3% (45/1 344) and 24.9% (334/1 344) of the B/plasma cells respectively. In the NEOLP group, they represented 31.6% (195/617), 59.6% (368/617), 0.2% (1/617) and 8.6% (53/617). Howerer, only plasma cells were detected in the NORMAL group. Spatial analysis revealed that B cells were actively involved in the formation of tertiary lymphoid structures (TLS) at various stages in OLP/OLL samples, with a prominent structural organization observed in secondary follicle-like TLS. Within these structures, the expressions of T cells marker gene CD3E and B cells marker gene MS4A1 were significantly elevated. Additionally, in secondary follicle-like TLS, the gene encoding follicular dendritic cell secreted protein, germinal center marker gene B cell lymphoma 6 and the gene for activation induced cytidine deaminase also showed strong expression. In OLP/OLL samples, plasma cell marker gene CD38, immunoglobulin (IGH) G3, IGHG1, IGHM, IGHD, IGHE, imunoglobulin Kappa constant, immunoglobulin alpha 1, immunoglobulin Lambda constant 1 and complement gene C3 all exhibited high levels of expression. <b>Conclusions:</b> Compared to normal mucosa, extensive B-cell infiltration is observed in both OLP and OLL, accompanied by significant differences in B-cell phenotypes and proportions. B cells appear to play a central role in local immune responses, primarily through the formation of TLS. However, the precise functional mechanisms underlying their involvement require further investigation.