Granzyme A-producing type 1 innate lymphoid cells promote salivary secretion in the aged submandibular gland.

BACKGROUND: Salivary gland function declines with age, contributing to periodontitis and aspiration pneumonia. However, the cellular mechanisms that preserve secretion during aging remain unclear. METHODS: Mice were stratified by aging stage, and saliva output and tissue histology were assessed. To infer cell-cell communication, regions surrounding lymphocyte clusters were microdissected and subjected to site-specific single-cell RNA sequencing. Epithelial cell responses were evaluated in a coculture system using a neutralizing antibody. Finally, physiological relevance was assessed by in vivo depletion, followed by quantification of changes in saliva secretion. RESULTS: Saliva production was maintained or modestly increased during early aging stages and coincided with the emergence of lymphoid cell clusters. Single-cell and interactome analyses identified Gzma + ILC1 subsets enriched in aged lymphoid cluster regions and predicted crosstalk with epithelial cells via a GZMA-Pard3 axis. Upregulation of epithelial Aqp5 expression was confirmed in vitro. In vivo depletion of ILC1s in aged mice significantly reduced stimulated saliva output, indicating that local ILC1-derived GZMA supports secretory capacity. CONCLUSIONS: Aged submandibular salivary glands accumulated ILC1s that promote epithelial function through a GZMA-dependent pathway and increased AQP5 expression, thereby maintaining salivary secretion during early aging. These findings identify ILC1s as regulators of salivary gland homeostasis and highlight the GZMA-Pard3 axis as a potential therapeutic target.