Interferon regulatory factor 5 expression levels regulate murine lupus in a type-I interferon-independent manner. Mus musculus

Polymorphisms in the transcription factor interferon regulatory factor 5 (IRF5) are strongly associated in human genetic studies with an increased risk of developing the autoimmune disease systemic lupus erythematosus. However, the biological role of IRF5 in lupus pathogenesis, if any, is not known. In this study we show that IRF5 is absolutely required for disease development in the FcgRIIB-/-Yaa and FcgRIIB-/- lupus models. In contrast to IRF5-sufficient FcgRIIB-/-Yaa mice, IRF5-deficient FcgRIIB-/-Yaa mice do not develop lupus manifestations and have a phenotype comparable to wildtype mice. Strikingly, full expression of IRF5 is required for the development of autoimmunity, as IRF5-heterozygotes had dramatically reduced disease. One effect of IRF5 is to induce the production of the type I interferon IFN-gamma, a cytokine implicated in lupus pathogenesis. To address the mechanism by which IRF5 promotes disease, we evaluated FcgRIIB-/-Yaa mice lacking the type I interferon receptor IFNAR1. Unlike the IRF5-deficient and IRF5-heterozygous FcgRIIB-/-Yaa mice, IFNAR1-deficient FcgRIIB-/-Yaa mice maintained a substantial level of residual disease. Furthermore, in FcgRIIB-/- mice lacking Yaa, IRF5-deficiency also markedly reduced disease manifestations, indicating that the beneficial effects of IRF5 deficiency in FcgRIIB-/-Yaa mice are not due only to inhibition of the enhanced TLR7 signaling associated with the Yaa mutation. Overall, we demonstrate that IRF5 plays an essential role in lupus pathogenesis in murine models and that this is mediated through pathways beyond that of type I interferon production. The fact that even IRF5 heterozygous mice developed minimal disease makes IRF5 a particularly attractive therapeutic target. Overall design: Serum samples from a total of 70 mice were run on the Utz Lab Whole Protein Autoantigen Array V1.0 (a single-color platform) in order to profile their autoantibodies against a library of autoimmune antigens. All samples were run once with no replicates. The samples consisted of the following groups: For data appearing in Figure 3D, illustrating that mice lacking IRF5 have their autoantibody levels significantly affected: R2Yaa IRF5+/+: 12 R2Yaa IRF5+/-: 11 R2Yaa IRF5-/-: 14 C57BL/6 ("WT" control): 13 Total mice (arrays) for this group: 50 For data appearing in Figure 6D, illustrating that mice lacking Ifnar1 do not have their autoantibody levels significantly affected: R2Yaa Ifnar+/+: 10 R2Yaa Ifnar-/-: 10 Total mice (arrays) for this group: 20

转录因子干扰素调节因子5（interferon regulatory factor 5, IRF5）的基因多态性在人类遗传学研究中与自身免疫性疾病系统性红斑狼疮（systemic lupus erythematosus）的发病风险升高显著相关。然而，IRF5在狼疮发病机制中的生物学作用（若存在）尚不明确。
本研究证实，IRF5是FcgRIIB-/-Yaa与FcgRIIB-/-狼疮模型疾病发生的绝对必需因子。与IRF5功能完整的FcgRIIB-/-Yaa小鼠不同，IRF5缺陷型FcgRIIB-/-Yaa小鼠不会出现狼疮表型，其表型与野生型小鼠相当。值得注意的是，IRF5的完整表达对自身免疫疾病的发生至关重要：IRF5杂合子小鼠的疾病症状显著减轻。IRF5的功能之一是诱导I型干扰素IFN-γ的产生，而该细胞因子已被证实与狼疮发病机制相关。
为探究IRF5促进疾病发生的分子机制，我们对缺失I型干扰素受体（IFNAR1）的FcgRIIB-/-Yaa小鼠进行了评估。与IRF5缺陷及IRF5杂合型FcgRIIB-/-Yaa小鼠不同，IFNAR1缺陷型FcgRIIB-/-Yaa小鼠仍存在一定程度的残留疾病症状。此外，在缺失Yaa的FcgRIIB-/-小鼠中，IRF5缺陷同样显著减轻了疾病表型，这表明FcgRIIB-/-Yaa小鼠中IRF5缺陷的有益效应并非仅由抑制Yaa突变相关的增强型Toll样受体7（TLR7）信号通路所介导。
综上，本研究证明IRF5在小鼠狼疮模型的发病机制中发挥核心作用，且其调控通路并非仅依赖于I型干扰素的产生。鉴于即使IRF5杂合子小鼠的疾病症状也极轻微，IRF5成为极具吸引力的治疗靶点。
整体实验设计：共计70只小鼠的血清样本被应用于Utz实验室全蛋白自身抗原阵列V1.0（单通道平台），以检测其针对自身免疫抗原库的自身抗体谱。所有样本均单次检测，未设置重复。样本分为以下组别：
1. 用于图3D数据（该数据证实IRF5缺陷小鼠的自身抗体水平显著改变）的分组：
R2Yaa IRF5+/+: 12只
R2Yaa IRF5+/-: 11只
R2Yaa IRF5-/-: 14只
C57BL/6 ("WT"野生型对照): 13只
该组总小鼠（阵列）数：50只
2. 用于图6D数据（该数据证实IFNAR1缺陷小鼠的自身抗体水平未发生显著改变）的分组：
R2Yaa Ifnar+/+: 10只
R2Yaa Ifnar-/-: 10只
该组总小鼠（阵列）数：20只