Mechanism of PD-1/PD-L1 in Regulating cTfr/cTfh Balance in Patients with Rheumatoid Arthritis

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.