The Salivary IgA Flow Rate Is Increased by High Concentrations of Short-Chain Fatty Acids in the Cecum of Rats Ingesting Fructooligosaccharides

Salivary immunoglobulin A (IgA) serves as a major effector in mucosal immunity by preventing submucosal invasion of pathogens. However, the mechanism by which consumption of fermentable fibers increases IgA in saliva was not fully elucidated. This study investigated the effects of fructooligosaccharides (FOS) intake and time after feeding on IgA levels in the saliva and cecal digesta and on the concentration of short-chain fatty acids (SCFA) in the cecum in rats. Five-week-old rats were fed a fiber-free diet or a diet with 50 g/kg FOS for zero, one, four, and eight weeks. Ingestion of FOS at one and eight weeks led to a higher IgA flow rate of saliva per weight of submandibular gland tissue (p < 0.05), which positively correlated with the concentration of SCFA in the cecal digesta (rs = 0.86, p = 0.0006, n = 12), but showed no correlation with the concentration of IgA in the cecal digesta (rs = 0.15, p = 0.3, n = 48). These results suggested that ingestion of FOS increased salivary IgA secretion through high levels of SCFA in the large intestine, which was produced by fermentation of FOS. Thus, continuously ingesting FOS for more than one week could increase secretion of salivary IgA.