Tehran University of Medical Sciences Iranian Journal of Allergy, Asthma and Immunology 1735-1502 23 3 2024 05 27 299 310 Yaqi Wang Medical School of Hebei University, Baoding, China AND Key Laboratory of Pathogenesis Mechanism and Control of Inflammatory-autoimmune Diseases, Baoding, China Min Zhang Medical School of Hebei University, Baoding, China AND Key Laboratory of Pathogenesis Mechanism and Control of Inflammatory-autoimmune Diseases, Baoding, China Shengde Chen Medical School of Hebei University, Baoding, China AND Key Laboratory of Pathogenesis Mechanism and Control of Inflammatory-autoimmune Diseases, Baoding, China Zheng Li Affiliated Hospital of Hebei University, Baoding, China Ming Meng Medical School of Hebei University, Baoding, China AND Key Laboratory of Pathogenesis Mechanism and Control of Inflammatory-autoimmune Diseases, Baoding, China 2023 11 27 2024 02 16 Rheumatoid arthritis (RA) is a type of autoimmune disease that results in immune disorder and excessive inflammatory response due to a reduction of self-tolerance. Invariant natural killer T (iNKT) cells can effectively alleviate clinical symptoms and hyper-inflammation in RA, but their mechanism of action is not well-defined. This study aims to investigate the mechanism of iNKT cell therapy for RA. We established a DBA/1 mouse model for RA and treated it with specific iNKT cells. A cytometric bead array was used to measure the amounts of cytokines in the serum. Flow cytometry was then employed to identify different subsets of helper T cells (Th), the frequency of conventional dendritic cells (cDC), the expression of CD80, CD86, programmed cell death ligand 1 (PD-L1), and PD-L2 on cDC surfaces, and associated pathway proteins. iNKT cell treatment reduced Th1/Th2 and Th17/ regulatory T (Treg) cell ratios while increasing interleukin-4 (IL-4) and IL-10. It enhanced the generation of immature cDCs, and it upregulated the level of PD-L2 by stimulating the signal transducer and activator of transcription 3 (STAT3) signaling pathway. Meanwhile, it activated the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway and inhibited the nuclear factor kappa B (NF-κB) pathway. According to our findings, iNKT cell treatment increased the expression of phosphates STAT3  in lymph node cDC, causing them to upregulate PD-L2 molecules. While activating the ERK1/2 pathway and inhibiting the NF-κB pathway, tolerogenic cDC was produced, restoring immune homeostasis and correcting excessive inflammation. These results deliver new insights into the treatment of RA by iNKT cells. https://ijaai.tums.ac.ir/index.php/ijaai/article/view/3960 https://ijaai.tums.ac.ir/index.php/ijaai/article/download/3960/2076