Dørum Siri, Qiao Shuo-Wang, Sollid Ludvig M, Fleckenstein Burkhard
Centre for Immune Regulation, Institute of Immunology, University of Oslo, and Rikshospitalet University Hospital, N-0027 Oslo, Norway.
J Proteome Res. 2009 Apr;8(4):1748-55. doi: 10.1021/pr800960n.
Celiac disease develops in genetically predisposed individuals as the result of an inappropriate intestinal immune response to dietary gluten proteins. T cells present in the intestine of celiac patients recognize gluten peptides in the context of HLA-DQ2 or -DQ8 molecules. Notably, T-cell recognition is increased after these peptides have been deamidated by the enzyme transglutaminase 2. Several T-cell epitopes of gluten exist, and most of these epitopes derive from the alcohol-soluble gliadin fraction. For some of these epitopes, specific T cells can be isolated from intestinal biopsies from nearly all patients, whereas for others, T-cell reactivity could be demonstrated in only a few patients. One reason for this observation could be that the rate of transglutaminase 2 (TG2)-mediated deamidation significantly differs between these peptides, resulting in different amounts of epitopes generated in vivo. In this study, we established a quantitative, mass spectrometry-based approach to measure the kinetics of TG2-mediated deamidation of gliadin-derived, DQ2-restricted epitopes. Our results demonstrate large variations in the degree of deamidation between different peptides and also between individual glutamine residues within each peptide. In general, alpha-gliadin derived epitopes that are frequently recognized by patient T cells showed a significant higher level of deamidation compared to the majority of epitopes from gamma-gliadin that are less frequently recognized. The degree of deamidation of individual residues within a peptide also seems to influence whether some epitopes are better recognized in context of DO2 or DQ8. Thus, the rate of deamidation by TG2 appears to be a factor of importance for the T-cell response to gluten in celiac disease.
乳糜泻在具有遗传易感性的个体中发生，是肠道对膳食谷蛋白产生不适当免疫反应的结果。乳糜泻患者肠道中的T细胞在HLA-DQ2或-DQ8分子的背景下识别谷蛋白肽段。值得注意的是，这些肽段被转谷氨酰胺酶2脱酰胺后，T细胞的识别作用增强。谷蛋白存在多个T细胞表位，其中大多数表位来自醇溶性麦醇溶蛋白部分。对于其中一些表位，几乎所有患者的肠道活检样本中都能分离出特异性T细胞，而对于其他表位，只有少数患者能检测到T细胞反应性。这一现象的一个原因可能是，这些肽段之间转谷氨酰胺酶2（TG2）介导的脱酰胺速率存在显著差异，导致体内产生的表位数量不同。在本研究中，我们建立了一种基于质谱的定量方法，以测定TG2介导的麦醇溶蛋白来源的、受DQ2限制的表位的脱酰胺动力学。我们的结果表明，不同肽段之间以及每个肽段内的单个谷氨酰胺残基之间的脱酰胺程度存在很大差异。一般来说，患者T细胞经常识别的α-麦醇溶蛋白来源的表位，与γ-麦醇溶蛋白中大多数较少被识别的表位相比，脱酰胺水平显著更高。肽段内单个残基的脱酰胺程度似乎也会影响某些表位在DQ2或DQ8背景下是否能被更好地识别。因此，TG2的脱酰胺速率似乎是乳糜泻中T细胞对谷蛋白反应的一个重要因素。
