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

Abstract

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.

Keywords: IgA; fructooligosaccharides; rats; saliva; short-chain fatty acid.

Figure 1

Effects of fructooligosaccharides (FOS) addition and time after feeding on the weight gain (A); flow rate of saliva (B); and weight of submandibular gland (C). n = 6 per group at each time. Symbols and vertical bars represent means and standard errors, respectively. There were no effects of interaction and FOS addition on weight gain, flow rate of saliva, and weight of submandibular gland (interaction: p = 0.8, 0.5, and 0.7, respectively; FOS addition: p = 0.9, 0.2, and 0.4, respectively, two-way analysis of variance (ANOVA)). Time after feeding affected weight gain, flow rate of saliva, and weight of submandibular gland (p < 0.0001, p < 0.0001, p < 0.0001, respectively).

Figure 2

Effects of fructooligosaccharides (FOS) addition and duration of feeding for test diets on the weight of cecal digesta (A); pH in cecal digesta (B); and IgA concentration in cecal digesta (C). n = 6 per group at each time. Symbols and vertical bars represent means and standard errors, respectively. There were interactions between FOS addition and intake period in the weight of cecal contents, pH in cecal digesta, and IgA concentration in cecal digesta (p = 0.0002, p < 0.0001, and p < 0.0001, respectively, two way ANOVA). * p < 0.05 versus control group at each week using Tukey’s multiple comparison.

Figure 3

Effects of fructooligosaccharides (FOS) addition and time after feeding on the tissue weight of cecum (A); concentration of IgA in saliva (B); and IgA flow rate in saliva per weight of submandibular gland tissue (C). n = 6 per group at each time. Symbols and vertical bars represent means and standard errors, respectively. There were interactions between FOS addition and intake period in the weight of cecal tissue, concentration of IgA, and IgA flow rate of saliva per weight of submandibular gland tissue (p < 0.0001, 0.03, and 0.0009, respectively, two-way ANOVA). * p < 0.05 versus control group at each week using Tukey’s multiple comparison.

Figure 4

Causal effects between fructooligosaccharides (FOS) addition in diets, IgA flow rate of saliva per rat submandibular gland tissue weight, weight of cecal tissue, weight of cecal digesta, pH in cecal digesta, and IgA concentration of cecal digesta using Bayesian network analysis. Causes and effects are indicated by arrowheads and lines, respectively. The Bayesian network showed that the IgA flow rate of saliva per weight of submandibular gland tissue was affected by SCFA concentration in cecal digesta, weight of cecal digesta and addition of dietary FOS. On the other hand, the IgA concentration in cecal digesta and the IgA flow rate of saliva per weight of submandibular gland tissue were not causally related.