Fig 2: Model of IL21‐AS1 regulating IL21 expression and Tfh differentiation in systemic lupus erythematosus (SLE) patients. IL21‐AS1 was highly expressed in CD4+ T cells of SLE patients and Tfh cells, which directly binds to promoter of IL21 gene and interacts with heterogeneous nuclear ribonucleoprotein U (hnRNPU) and CREB‐binding protein (CBP) protein to regulate H3 acetylation level in the promoter region of IL21. IL21‐AS1 overexpression promotes IL21 transcription activation and the aberrant differentiation of Tfh cells in SLE patients, thereby exacerbating autoimmune phenotypes of SLE. Red arrow indicates up‐regulation of expression. Green line with arrow indicates positive regulation.

Fig 3: IL21‐AS1 binding with heterogeneous nuclear ribonucleoprotein U (hnRNPU) regulates the epigenetic modifications. (A) Western blot detected the expression of hnRNPU protein in induced Tfh cells. (B) Western blot was used to verify the interference effect of si‐hnRNPU. (C) Representative flow diagram of Tfh cells and statistical analysis of Tfh cells proportions in siRNA‐hnRNPU group and siRNA‐control group. (D) ChIP‐qPCR analysed the enrichment level of hnRNPU in the IL21 gene proximal promoter region with hnRNPU antibody and IgG antibody in naïve CD4+ T and Tfh cell. (E) ChIP‐qPCR analysed the enrichment level of hnRNPU in the IL21 gene proximal promoter region in IL21‐AS1 anti‐sense oligonucleotide (ASO) group and control group. (F) H3K27 acetylation peak in the promoter region of IL21 according to public data (GSE177090, GSE177374, GSE177639 and GSE177926). (G) Co‐IP and western blot detected the interaction between hnRNPU and CREB‐binding protein (CBP) in Tfh cells. (H) ChIP‐qPCR analysed the enrichment level of CBP in the IL21 gene proximal promoter region in naïve CD4+ T and Tfh cell. (I) ChIP‐qPCR analysed the enrichment level of CBP in the IL21 gene proximal promoter region in IL21‐AS1 ASO group and control group. (J) ChIP‐qPCR detected the H3 acetylation (H3ac) level in IL21 proximal promoter region in naïve CD4+ T cells and Tfh cells. Data are representative of three independent experiments (mean ± SEM, n = 3). (K) ChIP‐qPCR detected the H3ac level in IL21 proximal promoter region in IL21‐AS1 ASO group and control group. *p < .05, **p < .01, ***p < .001 relative to controls. p‐Value of Tfh cells between control group and IL21‐AS1 ASO group was determined using two‐tailed paired‐samples t‐test, and others were determined using two‐tailed Student's t‐tests.