Rhamnogalacturonan‐I type polysaccharides isolated from Houttuynia cordata enzymatic hydrolysates activate intestinal immunity

BACKGROUND In our previous study, we developed enzymatic hydrolysates (HCPE) derived from Houttuynia cordata (HC) that exhibit Peyer's patch (PP)‐mediated immune activity. In this study, HCPE was fractionated using gel permeation chromatography, and the active moiety responsible for intestinal immunostimulatory activity was identified through activity‐guided fractionation based on PP–mediated assays. RESULTS HCPE was fractionated on a Sephadex G‐100 column into three distinct fractions – HCPE‐I, ‐II, and ‐III – which differed in molecular weight and chemical properties. Among these, HCPE‐I exhibited a potent PP‐mediated immunostimulatory effect, significantly enhancing cytokine secretion and bone marrow cell proliferation. Furthermore, HCPE‐I promoted mucin 2 expression in LS174T cells and enhanced tight junction integrity in Caco‐2 cells. Based on various structural characterization analyses, HCPE‐I was identified as a rhamnogalacturonan‐I (RG‐I) type polysaccharide with a molecular weight of 83.6 kDa, containing side chains composed of types I and II arabinogalactans and 1,5‐arabinan. CONCLUSION These findings provide valuable insights into the potential applications of HC‐derived polysaccharides as functional food ingredients or pharmaceutical agents for enhancing intestinal immune function. To the best of our knowledge, this is the first study to comprehensively investigate the immunological, biochemical, and physical aspects of intestinal immune modulation by an RG‐I type polysaccharide derived from HC.