Waxy hull-less barley intake enhances intestinal secretory IgA associated with dendritic cell activation in gut-associated lymphoid tissue.

Waxy hull-less barley (WHB), which is rich in β-glucan, reportedly exhibits immunomodulatory properties, but the underlying mechanism remains unclear. In this study, we investigated the immunological effects and underlying mechanism of a WHB-containing diet using DO 11.10 mice, in which the T-cell antigen (Ag)-specificity is largely restricted to ovalbumin to minimize WHB-specific adaptive immune responses. Fecal secretory IgA (SIgA) levels were consistently higher in the WHB intake group throughout the feeding period. In the ileum, expression of the IgA transporter polymeric immunoglobulin receptor (pIgR) and the retinoic acid-generating enzyme Raldh2 was significantly upregulated. WHB intake increased the ratio of MHCII+ CD86+ conventional dendritic cells (cDC) in the gut-associated lymphoid tissue (GALT) and peripheral blood, whereas no changes were observed in the spleen. IgA+ cells increased in peripheral blood but decreased in the GALT, whereas IgM+ and α4β7+ B cells were elevated in the GALT but reduced in the spleen. Microbiota analysis revealed increased α-diversity and a shift toward higher abundances of species in the butyrate-producing genera Oscillospira, accompanied by lower abundances of SMB53 and Allobaculum. Notably, the abundance of Allobaculum species was negatively correlated with fecal SIgA. These findings suggest that WHB consumption is associated with increased intestinal IgA secretion, activation of gut cDCs, upregulation of Raldh2 and pIgR, and coordinated changes in B-cell dynamics and the gut microbiota.