Genetic Modifiers Of Autoimmune Disease In FcgammaRIIB Mutant Mice

FcGammaRIIB是一种有效的狼疮易感基因，能够与多种其他基因座相互作用，改变自身免疫性疾病的发生和发展。在C57BL/6背景下，缺乏该分子的小鼠会出现自发的抗核抗体和致死性肾炎。BALB/c背景上的相同突变不明显，提示BALB/c背景上存在制约自身免疫发生发展的抑制子基因。为了研究这些背景遗传修饰物在B6.FcRIIB-/-疾病模型中的影响，我们进行了B6.FcRIIB-/-和BALB.FcRIIB-/-小鼠的杂交，并评估了所产生的F1和F2代的自身免疫表型。连锁分析表明，12号和17号染色体可能含有ANA与肾小球肾炎的正连锁区域。我们将注意力集中在12号染色体区域，因为到目前为止还没有在该区间发现明显的候选基因，因此增加了对该基因的精细定位将导致发现改变自身免疫性疾病易感性的新基因的可能性。新的同源菌株的产生使我们能够确定BALB/c基因组中12号染色体这一区域的存在足以使B6.R2-/-小鼠对狼疮病产生抵抗力。 我们分析了在B6.R2-/-小鼠中观察到的YAA基因修饰物在自身免疫性疾病进展中的作用。携带YAA基因的小鼠提供了一个很好的例子，说明了控制先天受体的表达是多么重要。在YAA小鼠中，B细胞和树突状细胞中的过度活跃表型与基因组易位相关，该易位导致至少17个基因的复制，其中之一是TLR7。虽然最初关于这种基因组复制的报道集中在该菌株对TLR7配体的高反应性，但由于多个基因重复的事实，该等位基因如何加速全身自身免疫的性质尚不清楚。例如，TLR7可能与其他一个或多个重复基因一起发挥作用，以增强病理上的加速，或者TLR7表达的增加可能仅仅与自身免疫的发展有关。因此，TLR7基因复制在Yaa小鼠中的确切重要性尚不确定。我们决定使用两种方法来回答这个问题，通过减少或增加TLR7基因剂量。当我们降低TLR7基因剂量时，我们能够消除YaA等位基因引起的高反应性，当我们培育FcGammaRIIB缺陷小鼠时，我们能够消除在YaA小鼠中看到的核仁抗体反应、病理增强和死亡率。这些数据清楚地表明，增加TLR7基因剂量可以增强系统自身免疫，因为通过降低TLR7基因剂量，YaA小鼠的表型完全恢复。 通过TLR7转基因小鼠的产生增加TLR7基因的剂量会导致急性全身性自身免疫性疾病的发展，其特征是抗RNA自身抗体的产生、肾小球肾炎、树突状细胞扩张、贫血和树突状细胞中的促炎干扰素特征。结合这两种技术，我们可以得出结论，TLR7基因剂量对于促进自身抗体的产生和狼疮相关的病理疾病来说是必要的，也是充分的。

FcgammaRIIB is a potent lupus susceptibility gene capable of interacting with a variety of other loci to modify both the induction and progression of autoimmune disease. Mice deficient in this molecule develop spontaneous anti-nuclear antibodies and fatal glomerulonephritis when on the C57BL/6 background. The same mutation on the BALB/c background is unremarkable, indicating the existence of suppressor loci on the BALB/c background which restrict the development of autoimmunity. To study the impact of these background genetic modifiers in the B6.FcRIIB-/- disease model, a cross between B6.FcRIIB -/- and BALB.FcRIIB -/- mice was performed and the resulting F1 and F2 generations evaluated for autoimmune phenotypes. Linkage analysis indicated that chromosomes 12, and 17 were likely to contain regions with positive linkage for ANA and glomerulonephritis. We have focused our attention to the Chromosome 12 region because far no obvious candidate genes have been found in that interval, thus increasing the likelihood that fine mapping of this locus will lead to the identification of novel genes that modify susceptibility of autoimmune disease. The generation of a new congenic strain has allowed us to determine that the presence of this region of chromosome 12 from the BALB/c genome is sufficient to render B6.R2-/- mice resistant to lupus disease. We analyze the effect of the Yaa genetic modifier in the progression of autoimmune disease observed in B6.R2-/- mice. Mice bearing the Yaa locus provide a prime example of how important it is to control the expression of innate receptors. In Yaa mice, a hyperactive phenotype in B and dendritic cells correlates with a genomic translocation that results in duplication of at least 17 genes, one of which being TLR7. While initial reports about this genomic duplication focused on hyperresponsiveness to TLR7 ligands in this strain, the nature of how this allele accelerates systemic autoimmunity remained unclear because of the fact that multiple genes are duplicated. For example, TLR7 could function with one or more of the other duplicated genes to potentiate the acceleration in pathology, or the increase in TLR7 expression may be merely correlative with the development of autoimmunity. Thus, the precise importance of TLR7 gene duplication in the Yaa mouse was undetermined. We decided to use two approaches to answer this question, by either decreasing or increasing TLR7 gene dosage. When we lowered TLR7 gene dosage we were able to ablate the hyperresponsiveness caused by the Yaa allele, and when bred to FcgammaRIIB-deficient mice we were able to eliminate the nucleolar antibody response, enhancement in pathology and mortality that is seen in the Yaa mouse. These data unmistakably showed that an increase in TLR7 gene dosage can potentiate systemic autoimmunity, as the phenotype of the Yaa mouse was completely restored through lowering TLR7 gene dosage. Increasing TLR7 gene dosage via the generation of TLR7 transgenic mice resulted in the development of acute systemic autoimmune disease characterized by anti-RNA autoantibody production, glomerulonephritis, dendritic cell expansion, anemia, and a pro-inflammatory interferon signature in the dendritic cells. The combination of these two techniques allows us to conclude that TLR7 gene dosage is both necessary and sufficient to promote autoantibody production and pathological disease associated with lupus.