Background and aims The aim of this study was to investigate the proportion of regulatory T cells (Tregs) in the peripheral blood mononuclear cells (PBMCs) of patients with systemic lupus erythematosus (SLE) compared with that of healthy controls (HCs). We also evaluated the differentiation difference of induced Tregs in vitro under the presence or absence of endoplasmic reticulum (ER) stress, which is one of the causal factors triggering lupus flares.

Methods We isolated the PBMCs of 16 SLE patients and 11 HCs. The percentage of CD4⁺CD25⁺FoxP3⁺ Tregs was analyzed using flow cytometry. The PBMCs were incubated with anti-CD3/CD28 beads, supplemented with transforming growth factor-β and interleukin-2 to induce differentiation of Tregs, with or without tunicamycin for 36 hours.

Results The percentage of Tregs in the PBMCs of SLE patients was lower than that in the HCs (1.8 ± 0.9 versus 2.6 ± 0.7%, p=0.02). The induced differentiation of Tregs increased in both groups, and the increased proportion was greater in the SLE group (600 ± 351 versus 252 ± 95%, p=0.01). Incubation with tunicamycin in the Treg differentiation process also increased the proportion of Tregs in both groups (385 ± 259 versus 166 ± 105%, p=0.006), and the increased proportion was higher in the SLE group.

Conclusions The baseline percentage of Tregs was lower in SLE patients than in HCs. However, when Treg differentiation was induced, the differentiation of Tregs was more pronounced in the SLE group. This exaggerated differentiation may reflect the paradoxical response to the diminished suppressive capacity of Tregs in SLE patients.