Abstract: Background: Periodontitis is a chronic inflammatory disease with high incidence and prevalence, leading to periodontal inflammation and tooth mobility. Microbial infection and host immune responses are the primary causative factors of periodontal tissue damage and progression. However, the intricate inflammatory reactions and dynamic changes of cell subsets in the immune microenvironment of periodontitis have not been fully clarified. Methods: To analyze the microenvironmental characteristics of inflammatory reactions in periodontal lesions, we performed single-cell transcriptome analysis, histology, immunohistochemistry, and flow cytometry on samples from three healthy volunteers and four patients with periodontitis, mapping single cells and identifying cell subtypes and their roles in the periodontal microenvironment. Results: Single-cell transcriptomic analysis showed that memory B cells located in periodontitis lesion microenvironments highly expressed transforming growth factor-β1(TGF-β1) and modulated macrophage phenotypic transformation, thereby promoting alveolar bone loss. In addition, cell?cell crosstalk involving macrophages and B lymphocytes was strengthened within inflamed periodontal tissues, which aggravated the damage to periodontal tissue. Conclusions: Based on single-cell sequencing datasets, we constructed a refined landscape of human gingival cellular subsets and cell interaction networks. Meanwhile, we uncovered previously unrecognized pro-inflammatory cell populations closely linked to chronic periodontitis, laying a foundation for advancing host-targeted therapeutic strategies.