Arabinogalactan from Cynanchum atratum induces tolerogenic dendritic cells in gut to restrain autoimmune response and alleviate collagen-induced arthritis in mice

Background: Rheumatoid arthritis (RA) is an autoimmune disease characterized by multiple joints lesions. Tolerogenic dendritic cells (tolDCs) play crucial roles in maintaining immune homeostasis. The immunomodulatory activity of plant-derived arabinogalactan (AGs) has been well investigated, however, whether AGs could suppress autoimmune responses by inducing tolDCs is remain unclear. Design: Collagen-induced arthritis (CIA, a mouse model of RA) mice were utilized to ascertain the role of AGs (obtained from Cynanchum atratum) in autoimmune responses. An antibiotic cocktail was administered to eliminate gut microbiota. Germ-free (GF) and Toll-like receptor 2 (TLR2) knockout mice were used to determine the function of AGs in intestinal immune cells. Results: The oral administration of dietary AGs substantially reduced the severity of CIA and rebalanced the ratio of regulatory T cells (Tregs) to T helper 17 (Th17) cells. Although the antibiotic cocktail depleted the mice's gut microbiota, AGs had a therapeutic effect on their CIA. AGs restored Treg/Th17 homeostasis by inducing CD103+ tolDCs, regardless of the gut microbiota of the GF mice. Coculture experiments confirmed that AGs induced tolDCs and transforming growth factor beta (TGF-beta) secretion, leading to Treg amplification. RNA sequencing and TLR2 knockout experiments revealed that AGs induced tolDCs through a TLR2-mediated mechanism. Preventive interventions with AGs established a tolerogenic intestinal immune microenvironment, which delayed the onset and progression of CIA. AGs functioned synergistically with tofacitinib, a JAK inhibitor, to effectively restore Treg/Th17 balance and alleviate CIA. Conclusion: This study introduces a novel microbiota-independent mechanism through which soluble dietary AGs inhibit systemic autoimmune responses. Our findings provide insights into the supplementation of dietary AGs in patients with preclinical or progressive RA.