Spermidine enhances Immunoglobulin A secretory capacity in rat salivary glands: An ex vivo study

Salivary Immunoglobulin A (IgA) plays a crucial role in mucosal immunity. However, the mechanisms that regulate its production are unclear. Spermidine (SPD), a polyamine involved in various cellular functions, has been implicated in immune modulation. In this study, we investigated the presence of SPD in rat salivary glands and its potential role in enhancing production of IgA.

Male Wistar rats were fed a low-polyamine diet for eight weeks. Submandibular and parotid glands were harvested and metabolomic analysis was used to determine the SPD concentration, reverse transcription quantitative polymerase chain reaction (RT-qPCR) was used to evaluate gene expression related to polyamine metabolism and autophagy, enzyme-linked immunosorbent assay (ELISA) was used to quantify secretion of IgA, and immunohistochemistry was used to localize spermidine synthase (SRM).

Metabolomic analysis revealed that the concentration of SPD was significantly higher in the submandibular gland than in the parotid gland. RT-qPCR revealed higher SRM and LC3b mRNA expression, and lower Rubicon expression in the submandibular gland. Ex vivo SPD supplementation significantly increased secretion of IgA from both glands. Immunohistochemistry confirmed strong SRM expression in the acinar and ductal cells of the submandibular gland.

These findings suggest that SPD is endogenously synthesized in rat salivary glands, particularly in the submandibular gland, and may enhance the ex vivo production capacity of IgA in salivary gland tissues. These results provide insights into the role of polyamines in mucosal immunity and suggest potential therapeutic applications of SPD in enhancing oral immune defense.