Fig. 3

In vitro blocking using PD-1-Fc increases the proliferative and cytokine-producing capacity of CD4⁺ T cells from patients with rheumatoid arthritis (RA). a and b CD4⁺ T cells were incubated with ligands L929-PD-L1 cells or PD-L1-Fc in the presence or absence of PD-1-Fc for 4 days. The in vitro proliferative response of CD4⁺ T cells from patients with RA to L929-PD-L1 cells or to PD-L1-Fc (0.5 μg/ml) was analyzed in the absence or presence of PD-1-Fc (0–1 μg/ml) using the Cell Counting Kit-8 method. OD optical density. The p value was calculated using the Mann–Whitney U test. Values are the mean ± standard deviation. *p < 0.05 versus controls. c Aliquots of peripheral blood mononuclear cells from patients with RA (n = 5) and healthy controls (HC) (n = 5) were incubated with a pool of CD3 antibody in the presence or absence of PD-1-Fc for 4 days. Brefeldin A was added for the last 16 h. The cells were then collected and stained for the cell surface markers CD4 and PD-1 and for the intracellular cytokines interferon (IFN)-γ, tumor necrosis factor (TNF)-α, interleukin (IL)-4, and IL-17A after fixation and permeabilization. PD-1 programmed cell death 1