Down‐Regulation–Resistant STAT4 Risk Haplotype Contributes to Lupus Nephritis Through CD4+ T Cell Interferon‐γ Production.

Objective: Variants in STAT4 are associated with systemic lupus erythematosus (SLE) and other autoimmune diseases. We undertook this study to investigate how disease‐associated variants affect STAT4 expression, in particular in CD4+ T cells where STAT4 plays an essential role. Methods: We compared Th1 differentiation between naive CD4+ T cells from healthy donors homozygous for the risk (R/R) or nonrisk (NR/NR) alleles. We analyzed epigenetic marks in STAT4 and evaluated the relevance of its third intron, assessed the consequences of Stat4 overexpression in vivo in mice, and analyzed the effects of the STAT4 genotype in patients with lupus nephritis. Results: Naive CD4+ T cells from NR/NR healthy donors down‐regulated STAT4 in response to interleukin‐12 (IL‐12). In contrast, cells from R/R healthy donors maintained high levels. R/R cells exhibited a higher abundance of transcriptionally active STAT4 and increased interferon‐γ production. Accordingly, R/R healthy donors exhibited a stronger induction of local active enhancer marks. Genetic editing confirmed the presence of a negative regulatory region in the STAT4 third intron, where most of the SLE‐associated STAT4 single‐nucleotide polymorphisms (SNPs) are located. In vivo forced expression demonstrated that increases in Stat4 levels in T cells enhanced glomerulonephritis in mice. Accordingly, the R/R genotype was associated with suboptimal response to treatment and with worse clinical outcomes in patients with proliferative lupus nephritis. Conclusion: The SLE‐associated STAT4 haplotype correlates with an abnormal IL‐12–mediated STAT4 transcriptional regulation. Carriers of the risk variant exhibit exaggerated CD4+ proinflammatory capacities that, in the context of SLE, contribute to more severe disease. R/R patients may benefit from blockade of the IL‐12/STAT4 pathway. [ABSTRACT FROM AUTHOR]