Intestinal D-amino acids content is highly related to intestinal IgA production upon soluble dietary fiber ingestion in mice

Soluble dietary fiber (SDF) induces intestinal IgA production. Mechanistically, this has primarily been explained by intestinal bacteria producing short-chain fatty acids (SCFAs) as metabolites from the SDF. Here, we aimed to identify factors other than SCFAs that contribute to SDF-induced intestinal IgA production. SDF ingestion (3 % of the diet) for 9–12 weeks induced a four-fold increase in fecal IgA production in BALB/cA mice. The total SCFA concentration in the cecum tends to show a positive correlation with fecal IgA content (ρ = 0.5734, P = 0.0513), while the content of D-amino acids (D-AAs), inducers of IgA, in the cecum and colon exhibited a strongly positive correlation with the IgA content (ρ = 0.7805, P < 0.001). Bacterial flora analysis of fecal samples revealed that certain bacterial species were highly correlated with IgA production. These findings suggest that D-AAs play an important role in SDF-induced intestinal IgA production.