Multidimensional immunomodulation by abelmoschi corolla polysaccharide: Gut barrier restoration, microbiota remodelling, and systemic metabolic regulation

BACKGROUND: The dried flower (corolla) of Abelmoschus manihot (L.) Medicus, known as Abelmoschi Corolla, contains polysaccharides with therapeutic potential for immunopotentiation; however, the underlying mechanisms remain unclear. PURPOSE: This study aimed to systematically investigate the efficacy and molecular mechanisms through which acidic Abelmoschi Corolla polysaccharides (S-AMFP) reverse cyclophosphamide (CTX)-induced immunosuppression, using integrated analyses of intestinal microbiology, metabolomics, histology, and biochemistry. METHODS: We isolated and purified S-AMFP from Abelmoschi Corolla and subjected it to preliminary structural characterisation. An immunosuppressive mouse model was established through intraperitoneal injection of cyclophosphamide (CTX). The immunorestorative effects of S-AMFP were evaluated using gut microbiomics, non-targeted metabolomics, histopathology, and molecular biology techniques. Immune organ indices, including spleen and thymus weights, were measured in BALB/c mice. Cytokine and immunoglobulin levels (TNF-α, IL-4, IL-6, IgG, IgA, and IgM) were quantified using enzyme-linked immunosorbent assay; T-lymphocyte subsets (CD3⁺/CD4⁺ percentages and CD4⁺/CD8⁺ ratios) were analysed using flow cytometry. Splenic histopathological changes were examined using haematoxylin and eosin staining. Gut microbiota composition was profiled by 16S rDNA sequencing, whereas serum metabolites were analysed through non-targeted metabolomics. Faecal short-chain fatty acids (SCFAs) were quantified using gas chromatography-mass spectrometry. Mitogen-activated protein kinase pathway activity and intestinal barrier integrity were evaluated using reverse transcription quantitative polymerase chain reaction and Western blot. RESULTS: S-AMFP is a pectin-based polysaccharide primarily composed of rhamnose and galacturonic acid. S-AMFP restored body weight, thymic and splenic indices, serum cytokines, immunoglobulin levels, and rectified T lymphocyte dysfunction by rebalancing CD4⁺/CD8⁺ ratios. It improved intestinal barrier function by up-regulating tight junction proteins (Claudin-1 and Occludin), activating the MAPK pathway, and reshaping gut microbiota. S-AMFP increased beneficial bacteria, including Lactobacillus and Lachnospiraceae_NK4A136_group, reduced pathogenic Enterobacteriaceae, elevated SCFA levels, and alleviated CTX-induced metabolic disturbances in amino acid, lipid, and energy pathways. CONCLUSIONS: S-AMFP mitigates CTX-induced immunosuppression by restoring intestinal barrier integrity, modulating gut microbiota composition, and enhancing metabolic homeostasis. These findings advance current understanding of polysaccharide-mediated immunomodulation and highlight S-AMFP's potential as a dietary supplement or adjunctive agent for mitigating drug-induced immunosuppression, particularly through gut ecological and metabolic regulation.