Tehran University of Medical Sciences Iranian Journal of Allergy, Asthma and Immunology 1735-1502 23 5 2024 10 06 539 549 Xiuzhen Wang Department of Rheumatology and Immunology, First Affiliated Hospital of Jinzhou Medical University, Jinzhou, China Caijie Liu Department of Ultrasound, First Affiliated Hospital of Jinzhou Medical University, Jinzhou, China 2024 01 07 2024 04 17 Rheumatoid arthritis (RA) is frequent, an imbalance between helper cells (Th) and regulatory T cells (Treg) is the fundamental immunological cause of RA. This study investigates how recombinant human programmed cell death 1 (PD-L1) protein affects circulating T follicular helper (cTfh), circulating T follicular regulatory (cTfr), and their equilibrium. Magnetic bead sorting was used to select CD4+CXCR5+T cells from RA patients' and healthy individuals' peripheral blood mononuclear cells for in vitro growth. Recombinant human PD-L1 protein stimulated CD4+CXCR5+T cells. Cell counting kit 8 (CCK-8), flow cytometry surface labeling, ELISA, and RT-PCR were used to measure CD4+CXCR5+T cell proliferation inhibition, cTfh and cTfr frequencies, IL-21 expression, and PI3K, AKT, Bcl-6, and Blimp-1 mRNA levels. The recombinant human PD-L1 protein dose-dependently inhibited the proliferation of CD4+CXCR5+T cells in active RA peripheral blood. However, it has a weaker inhibitory effect on healthy peripheral blood CD4+CXCR5+T cells. PD-L1 protein decreased cTfh in active RA peripheral blood CD4+CXCR5+T overall cultured cells but did not affect cTfr; The cTfr/cTfh ratio increased but did not affect the frequency of cTfh and cTfr in healthy persons' cultured CD4+CXCR5+T cells. PD-L1 protein reduced IL-21 in CD4+CXCR5+T cell culture supernatant from active RA peripheral blood. Recombinant human PD-L1 protein lowered PI3K, AKT, and Bcl-6 mRNA in active RA peripheral blood CD4+CXCR5+T cell culture, including significant differences. But Blinmp-1 mRNA variations were neither substantial nor statistically different. PD-1/PD-L1 limits cTfh proliferation, differentiation, and activation via the PI3K/AKT signaling pathway regulates its immunological balance with cTfr, and corrects the cTfr/cTfh imbalance by controlling their interaction.  https://ijaai.tums.ac.ir/index.php/ijaai/article/view/3993 https://ijaai.tums.ac.ir/index.php/ijaai/article/download/3993/2120