Salivary Microbiota From a Periodontitis Donor Is Associated With Altered <scp>IgA</scp> ‐Related Immune Features in Germ‐Free Mice

AIM: The oral microbiota has been implicated in mucosal immune regulation; however, its causal impact on salivary gland-associated immune features remains incompletely understood. In this proof-of-concept study, germ-free (GF) mice were colonised with salivary microbiota derived from either a periodontitis donor or a periodontally healthy donor, and IgA-associated immune readouts were evaluated across multiple compartments. METHODS: GF mice were orally colonised with saliva-derived microbiota from a periodontitis patient or a periodontally healthy donor (or PBS). Total IgA in saliva, serum and faeces were quantified by ELISA. Cervical lymph nodes and blood were analysed by flow cytometry. Submandibular glands underwent histology and bulk RNA-seq. RESULTS: cell signals and IgA immunoreactivity in the submandibular glands. Transcriptomic analysis revealed heterogeneous expression of individual IgA-related genes, with coordinated patterns observed at the level of IgA/mucosal defence-related gene sets. CONCLUSIONS: These findings indicate that salivary microbiota from a periodontitis donor are associated with altered IgA-related immune features under GF conditions. While limited by the use of a single donor per group, this study provides proof-of-concept evidence supporting a potential role of oral microbiota in shaping salivary gland-associated immune characteristics.