Fig. 1

a Gating strategy for flow cytometry analyses of interleukin-21 (IL-21) production in CD4+CD45RO+/− T cells and CD4+CD56+ NK T cells. An fluorescence minus-one control was used to gate on CD56. b IL-21 production in immune cell subsets. Expression levels of IL-21 measured by flow cytometry in immune subsets of cells from systemic lupus erythematosus (SLE) patients (n = 6) and healthy controls (HC) (n = 7). Memory Th cells (CD4+CD45RO+) and naïve Th cells (CD4+CD45RO-) from SLE patients showed increased production of IL-21 upon stimulation compared to HC. Bar indicates median. **p < 0.01, ***p < 0.001 (Mann–Whitney U-test). c IL-21 mRNA expression levels. mRNA expression levels of IL-21 in purified CD4+ T cells from SLE patients (n = 12) and HC (n = 7). Bar indicates median. *p < 0.05 (Mann–Whitney U-test). d Autocrine induction of IL-21. mRNA expression levels of IL-21 in purified CD4+ T cells from SLE (n = 6) patients and HCs (n = 5) stimulated with IL-21 at indicated time points with and without the STAT3 inhibitor cucurbitatin I (CucI). Cells not treated with CucI were treated with the vehicle (DMSO). After 3 hours of IL-21 stimulation, IL-21 expression levels were significantly higher in DMSO-treated HC and significantly lower in CucI-treated CD4+ T cells compared to their respective baselines. Graph shows mean ± SEM. *p < 0.05 (Mann–Whitney U-test). NK natural killer, SS side-scatter