Understanding how perturbations in microbial mimicry promotes breakdown in tolerance to insulin

背景1型糖尿病(T1D)是一种自身免疫性疾病，由T细胞介导的产生胰岛素的胰岛细胞破坏引起。人类白细胞抗原(HLAII)类分子的多态性是T1D的主要遗传危险因素。最近，一种宿主-微生物组相互作用，解释了人类白细胞抗原II类的易感性，已经被描述为1。这篇论文鉴定了识别与T1D易感II类分子DQ8结合的胰岛素微生物模拟物的交叉反应T细胞。具有T1D保护作用的HLA-DQ6分子强烈结合了胰岛素的微生物模拟物，这与交叉反应调节T细胞(Treg)在降低疾病风险方面的作用一致。而易感T1D的HLA-DQ8分子与这些多肽的结合较弱，有利于交叉反应效应T细胞(TEF)从胸腺逃逸，并增强了抗胰岛素自身免疫。大多数模拟微生物属于转酮醇酶(TKT)超家族。TKT是一种参与处理膳食纤维的酶，在婴儿断奶期间表达上调。从牛奶到固体食物的这种转变，导致肠道微生物区系迅速扩张，是形成耐受性的关键时期。由于胰岛素的第一批自身抗体最常出现在9-18个月大的断奶后，这表明这是自身免疫性糖尿病的主要原因。我们假设微生物-TKT的异常表达破坏了免疫稳态，有利于交叉反应T细胞的激活，从而触发对胰岛素的自身免疫。这些干扰很可能是由表达不适当数量的TKT的非生物微生物分类群驱动的。研究设计通过GPPAD协会4，5，从670名根据遗传风险评分(GRS)6有T1D高风险的儿童收集纵向粪便和血液样本。自身抗体水平、血液代谢物和肠道微生物群的纵向变化将通过T1D-GRS、T1D自身抗体的存在和临床状态进行监测和分层。在我们的实验室，从DMech-Biome项目收集了445名婴儿(8周和8个月大时)的唾液和大便样本。由于这些参与者不是根据T1D-GRS选择的，他们可以作为人口控制队列。将分析微生物组组成、人类白细胞抗原单倍型和其他遗传风险基因座之间的相互作用。元基因组分析的纵向比较将使人们能够深入了解断奶和早期生活过程中肠道微生物组组成的变化。这种分析可以推断微生物-TKT表达的变化，并识别可能促进交叉反应T细胞激活的潜在的非生物微生物分类群。开发HLA四聚体将评估识别胰岛素和微生物-TKT多肽的交叉反应T细胞的存在。评估不同的人类白细胞抗原II类四聚体，结合微生物背景分子，再加上荧光激活的细胞分选，将允许深入了解不同的人类白细胞抗原单倍型如何有利于交叉反应T细胞的产生。这可以评估耐受性微生物上下文分子是否可以通过易感的HLA分子在呈现的情况下促进Treg的产生。影响本项目的目的是评估在生命早期发育的非生态型、促炎性微生物群是否会通过微生物-TKT的不适当表达和呈现而增加发生T1D的风险。通过纵向评估，微生物区系内的变化和微生物-TKT的表达可以与T1D自身抗体的发展和临床状态相比较。微生物菌株的鉴定，对于通过激活交叉反应Treg来赋予耐受性很重要，可以为预防性微生物组靶向治疗的发展提供信息。加西亚，A.R.等人《2022年医学评论》4.齐格勒，A.G.等人，20192英国医学杂志公开赛。瓦塔宁等人2018年《自然》5.齐格勒等人《英国医学杂志》公开赛20213。Al Nabhani，Z.等人的豁免权2019年6.雷东多

BackgroundType 1 diabetes (T1D) is an autoimmune disease, resulting from T-cell mediated destruction of insulin-producing pancreatic islet cells. Polymorphisms of human leukocyte antigen (HLA) class II molecules are major genetic risk factors for T1D. Recently, a host-microbiome interaction, explaining HLA class II susceptibility, has been characterised1. This paper identified cross-reactive T cells that recognised microbial-mimics of insulin bound to the T1D-predisposing class II molecule DQ8. The T1D-protective HLA-DQ6 molecule strongly bound microbial mimics of insulin, consistent with a role for cross-reactive regulatory T cells (Treg) in lowering disease risk. While the T1D-predisposing HLA-DQ8 molecule bound these peptides more weakly, favouring escape of cross-reactive effector T cells (Teff) from the thymus and increased anti-insulin autoimmunity. The majority of microbial-mimics belonged to the transketolase (TKT) superfamily. TKT is an enzyme involved in processing dietary fibre and is upregulated during infant weaning2. This transition, from milk to solid food, induces rapid expansion of gut microbiota, and is a critical period for developing tolerance3. As the first autoantibodies to insulin appear most often post-weaning, at 9-18 months of age, this suggests a primary cause of autoimmune diabetes.We hypothesise that aberrant expression of microbial-TKT disrupts immune homeostasis, favouring activation of cross-reactive Teffs, to trigger autoimmunity against insulin. These perturbations are likely to be driven by dysbiotic microbial taxa, expressing inappropriate amounts of TKT. Research DesignThrough the GPPAD consortium4,5, longitudinal stool and blood samples have been collected from 670 children, with a high risk of T1D based on their genetic risk score (GRS)6. Longitudinal changes in autoantibody levels, blood metabolomes, and gut microbiome will be monitored and stratified by T1D-GRS, presence of T1D-autoantibodies, and clinical status.In our lab, from the DMech-biome project, saliva and stool samples (at 8 weeks and 8 months of age) from 445 infants have been collected. As these participants have not been selected based on T1D-GRS, they can act as a population control cohort. Interactions between the microbiome composition, HLA-haplotypes, and other genetic risk loci will be analysed. Longitudinal comparisons of metagenomic analysis will allow insights into changes in gut microbiome composition across weaning and early life. This analysis could infer changes in microbial-TKT expression, and identify potential dysbiotic microbial taxa that may promote activation of cross-reactive Teff.Development of HLA tetramers will assess the presence of cross-reactive T cells recognising both insulin and microbial-TKT peptides. Assessment of different HLA class II tetramers in combination with microbial context-molecules, coupled with fluorescent-activated cell sorting, will allow insight into how different HLA-haplotypes favour production of cross-reactive Teffs. This could assess whether tolerogenic microbial context-molecules could promote Treg production despite presentation through predisposing HLA molecules.ImpactThis project aims to assess whether development of a dysbiotic, proinflammatory microbiome in early life can increase risk of developing T1D, through inappropriate expression and presentation of microbial-TKT. Through longitudinal assessment, changes within microbiota taxa and expression of microbial-TKT can be compared to development of T1D autoantibodies and clinical status. The identification of microbial strains, important for conferring tolerance through activation of cross-reactive Treg could inform development of preventative microbiome-targeted therapies.References1. Garcia, A. R. et al MedXiv 2022 4. Ziegler, A. G. et al BMJ Open 20192. Vatanen, T. et al Nature 2018 5. Ziegler, A. G. et al BMJ Open 20213. al Nabhani, Z. et al Immunity 2019 6. Redondo