Gradehandt G, Hampl J, Plachov D, Reske K, Rüde E
Institut für Immunologie der Johannes Gutenberg Universität, Mainz, Fed. Rep. Germany.
Immunol Rev. 1988 Dec;106:59-75. doi: 10.1111/j.1600-065x.1988.tb00773.x.
In this study we investigated aspects of antigen processing using insulin and insulin A chain-derived fragments as model antigens in Ab alpha Ak beta-restricted T-cell stimulation. Similarly to other proteins, the immunodominant region of insulin recognized by these T cells is limited in size. It is located on the insulin A chain and encompasses a portion of the molecule that is represented faithfully by peptide A1-14(SSO3-)3. Efficient presentation of intact insulin and its entire A chain is dependent on uptake and processing by APC. Whereas peptides stemming from various globular proteins are known to be presented to T cells by APC without requiring processing, this is not the case with A-chain fragment A1-14 (SSO3-)3. This observation suggested that, in addition to proteolytic degradation, other mechanisms might play a role in the processing of these antigens. Three cys-residues are located in close proximity to those amino acid residues of the insulin A chain that are inferred to participate in the specific interaction with MHC class II molecules and the TcR. In A-chain derivatives that are stimulatory for the T cells or in intact insulin these cys residues are engaged in disulfide bonds or are S-sulfonated. Both linkages can be reversibly modified by reaction with thiols. Functional data indicate that from intact insulin and from structurally distinct A-chain derivatives a closely similar or identical peptide is formed and bound to class II molecules for recognition by the T cells. The question arises as to whether, in this processed peptide, the cys residues are present in reduced form, engaged in disulfide bonds, or are modified in some other way. Taken together, these findings suggest that modification of cys residues or isomerization of disulfide bonds may play a role in insulin processing. It can be expected that other proteins carrying cys residues in their immunodominant peptides may show similar processing requirements. The inhibition of N-glycosylation of proteins by tunicamycin in APC blocked the processing and presentation of insulin and OvA whereas, under the same conditions, the presentation of a processing-independent peptide was not affected. Furthermore, an autoreactive T-cell clone was capable of recognizing tunicamycin-treated APC. Since the expression of class II molecules was found to be unaltered as demonstrated by cytofluorometric analysis the deficient N-glycosylation appears to have little influence on class II antigen-mediated T-cell recognition but interferes with uptake of antigen and/or its processing by APC.
在本研究中，我们以胰岛素和胰岛素A链衍生片段作为模型抗原，在AbαAkβ限制的T细胞刺激中研究了抗原加工的各个方面。与其他蛋白质类似，这些T细胞识别的胰岛素免疫显性区域大小有限。它位于胰岛素A链上，包含分子的一部分，肽A1-14(SSO3-)3能忠实地代表这部分分子。完整胰岛素及其整个A链的有效呈递依赖于抗原呈递细胞（APC）的摄取和加工。虽然已知来自各种球状蛋白质的肽可由APC呈递给T细胞而无需加工，但A链片段A1-14(SSO3-)3并非如此。这一观察结果表明，除了蛋白水解降解外，其他机制可能在这些抗原的加工中起作用。三个半胱氨酸残基紧邻胰岛素A链中推断参与与MHC II类分子和T细胞受体（TcR）特异性相互作用的氨基酸残基。在对T细胞有刺激作用的A链衍生物或完整胰岛素中，这些半胱氨酸残基参与二硫键形成或被S-磺化。两种连接都可通过与硫醇反应进行可逆修饰。功能数据表明，从完整胰岛素和结构不同的A链衍生物中形成了紧密相似或相同的肽，并与II类分子结合以供T细胞识别。问题在于，在这个加工后的肽中，半胱氨酸残基是以还原形式存在、参与二硫键形成，还是以其他方式修饰。综上所述，这些发现表明半胱氨酸残基的修饰或二硫键的异构化可能在胰岛素加工中起作用。可以预期，在其免疫显性肽中携带半胱氨酸残基的其他蛋白质可能表现出类似的加工要求。衣霉素对APC中蛋白质N-糖基化的抑制作用阻断了胰岛素和卵清蛋白（OvA）的加工和呈递，而在相同条件下，与加工无关的肽的呈递不受影响。此外，一个自身反应性T细胞克隆能够识别经衣霉素处理的APC。由于细胞荧光分析表明II类分子的表达未改变，缺乏N-糖基化似乎对II类抗原介导的T细胞识别影响很小，但会干扰APC对抗原的摄取和/或其加工。
