Immunoregulatory Defects In Inflammatory Bowel Disease

为了探讨NOD2 NBD突变引起的疾病机制，我们首先确定了过表达的完整NOD2或带有Blau突变的NOD2 (BS-NOD2) （R314W）交叉（下调）调节tnbs -结肠炎基础上的TLR反应的能力。虽然过表达完整的NOD2可以保护小鼠免受tnbs -结肠炎，但过表达BS-NOD2却没有保护作用。这些发现得到了对携带NOD2敲入突变的小鼠的研究的证实，这些小鼠与BS患者相似，在研究中我们发现，与对照组小鼠相比，NOD2配体（muramyl dipeptide， MDP）给药对dss -结肠炎的保护作用不强。重要的是，这些保护失败也在杂合小鼠中被注意到，其中突变只发生在一个等位基因上；因此，突变的NOD2发挥显性负作用，这解释了Blau突变具有常染色体显性效应的事实。

To probe the mechanism of disease caused by mutations in the NBD of NOD2 we first determined the capacity of over-expressed intact NOD2 or NOD2 with a Blau mutation (BS-NOD2) (R314W) to cross (down)-regulate TLR responses underlying TNBS-colitis. Whereas over-expression of intact NOD2 protected mice from TNBS-colitis, over-expression of BS-NOD2 failed to protect. These findings were corroborated by studies of mice bearing a knock-In mutation of NOD2 similar to that in patients with BS in which we showed that such mice were not as protected from DSS-colitis by NOD2-ligand (muramyl dipeptide, MDP) administration as was comparably treated littermate control mice. Importantly, these failure to protect was also noted in heterozygous mice in which the mutation occurred on only one allele; thus the mutated NOD2 exerted a dominant negative effect which explained the fact that the Blau mutation has an autosomal dominant effect. Studies conducted to investigate the molecular basis of these cross-regulatory defects indicated that BS-NOD2 expressed in HEK293T cells exhibit a reduced ability to oligomerize, interact with or activate RIPK2 and activate NF-kappaB. In addition, MDP-stimulated cells from BS-NOD2 KI mice fail to up-regulate expression of IRF4, a factor that has been shown to mediate NOD2 cross-regulation by de-ubiquitination of NF-kappaB signaling components. Indeed, lack of IRF4-mediated cross-regulatory function in KI cells was shown by the fact that enhanced TLR responses exhibited by these cells are suppressed by lentivirus transduction of IRF4. Overall, these studies indicate that NOD2 bearing a BS mutation lacks the ability to cross-regulate TLR responses via its inability to activate IRF4. The mutation thus renders BS patients susceptible to excessive TLR responses that have the potential to support inflammation at sterile tissue sites. Thus, the Blau mutation affecting NOD2 causes inflammatory disease by affecting NOD2 immunoregulatory function.