We have demonstrated previously that Asn-Pro-Trp-Asp-Gln (NPWDQ, amino acids 107-111 of as 2 -casein) inhibited allergen permeation, such as that demonstrated by ovalbumin, using Caco-2 cells as an in vitro human intestinal epithelial model and in mouse jejunal and ileal loops ex vivo. In the present study, the mechanism underlying this inhibitory activity was examined in Caco-2 cells. Transepithelial resistance value increased in response to the addition of increasing NPWDQ concentrations (10 26 -10 24 M), which suggests that this peptide enhanced epithelial barrier function. Next, changes in mRNA expression by the addition of NPWDQ (10 26 M) were analysed in Caco-2 cells using the microarray method. NPWDQ up-regulated the expression of the occludin gene in cells, but the level of the genes of the claudin family and zonula occludens-1 (ZO-1) was unchanged. Increased protein expression of occludin, but not of claudin-1 or of ZO-1, was also observed. Therefore, it is suggested that NPWDQ up-regulated the expression of occludin in particular and enforced the tight junction barrier. These data imply that a food-derived peptide can fine-tune the epithelial barrier.

We evaluated the effects of a 50% methanol extract of Citrus unshiu powder (MEC) on cytokines in peripheral blood mononuclear cells (PBMCs) obtained from patients with seasonal allergic rhinitis to cedar pollen. The levels of cytokines, such as TNF-alpha, IFN-gamma, IL-2, IL-4, IL-5, IL-10, IL-12 (p70), IL-13, and GM-CSF, produced by pollen-stimulated PBMC were measured. We found that MEC suppressed pollen-induced TNF-alpha release and increased IFN-gamma release from PBMCs. The results suggest that Citrus unshiu powder has an immunomodulatory effect in vitro and that its use could improve seasonal allergic rhinitis symptoms.