Structural characterization of an RG-II-associated complex pectic polysaccharide from Typha angustifolia pollen with dendritic cell-modulating activity

BACKGROUND: Pectic polysaccharides from medicinal plants are promising natural immunomodulators, but their structural heterogeneity has hindered the identification of bioactive domains and limited their further development. The structural basis underlying their regulation of dendritic cell-mediated immune responses remains poorly understood. PURPOSE: This study aimed to characterize PTPS-1-3, a pectic polysaccharide isolated from Typha angustifolia pollen, and evaluate its effects on dendritic cell maturation and antigen-specific T-cell activation. METHODS: PTPS-1-3 was characterized by molecular weight determination, monosaccharide composition analysis, methylation analysis, multidimensional nuclear magnetic resonance spectroscopy, and partial acid hydrolysis. Its immunomodulatory activity was evaluated in bone marrow-derived dendritic cells (BMDCs) by assessing cell viability, maturation markers, cytokine secretion, and phagocytic capacity. Transcriptomic analysis and an OT-I co-culture system were used to investigate the underlying pathways and antigen-specific CD8⁺ T-cell responses. Structure-activity relationships were explored by comparison with a partial acid hydrolysate and a homogalacturonan-type polysaccharide. RESULTS: PTPS-1-3 was an approximately 10 kDa pectic polysaccharide composed mainly of rhamnose, arabinose, xylose, galactose, and galacturonic acid. It contained homogalacturonan regions, arabinogalactan-II-rich side chains, and rhamnogalacturonan-II-associated motifs. PTPS-1-3 promoted BMDC maturation without detectable cytotoxicity, as shown by increased CD40, CD80, and CD86 expression, enhanced TNF-α, IL-1β, and IL-6 secretion, and reduced phagocytic capacity. Transcriptomic analysis revealed enrichment of antigen processing and presentation pathways. PTPS-1-3-treated BMDCs further enhanced antigen-specific CD8⁺ T-cell activation, proliferation, and IFN-γ and TNF-α production. Comparative analysis suggested that the immunomodulatory activity of PTPS-1-3 may be associated with its intact and complex branched pectic architecture, although differences in molecular weight may also contribute to the observed activity. CONCLUSION: PTPS-1-3 promotes BMDC maturation and enhances subsequent antigen-specific CD8⁺ T-cell responses. Its immunomodulatory activity may be associated with the integrity and complexity of its pectic architecture, while the contribution of molecular weight and individual structural features requires further clarification.