Dodi A I, Brett S, Nordeng T, Sidhu S, Batchelor R J, Lombardi G, Bakke O, Lechler R I
Department of Immunology, Royal Postgraduate Medical School, London, GB.
Eur J Immunol. 1994 Jul;24(7):1632-9. doi: 10.1002/eji.1830240727.
The human fibroblast cell line, M1, expressing the products of transfected DRA and DRB1*0101 genes (M1-DR1) was unable to present intact influenza antigens to a series of DR1-restricted human T cell lines and clones, but was fully able to present synthetic peptides for T cell recognition. In contrast, M1-DR1 cells infected with live influenza virus were recognized by two polyclonal hemagglutinin- or whole virus-specific T cell lines and one of four T cell clones. This difference could not be accounted for simply by the ability of infectious virus to overcome a defect in antigen uptake by the M1-DR1 cells, in that direct studies of endocytosis showed that the M1 cells were more efficient than human B cells in the internalization of exogenous protein. These data suggested that the M1 cells were unable to present exogenous antigens but were capable of loading major histocompatibility complex (MHC) class II molecules with peptides derived from endogenous antigens. To investigate this further, the M1-DR1 cells were super-transfected with a cDNA encoding the p33 and p35 forms of the human invariant chain (Ii). Expression of the Ii chain was detected by intracytoplasmic staining of transfectants, and by metabolic labeling. Equimolar amounts of the p33 and p35 forms were detected, and the high level of p35 Ii was reflected by extensive retention of Ii protein in the endoplasmic reticulum. Addition of the Ii chain led to no recovery of presentation of intact antigens with DR1, but inhibited the presentation of live virus. These data indicate that MHC class II molecules in the M1-DR1 cells can be loaded with peptides derived from endogenous proteins, possibly in the biosynthetic pathway, and that the Ii chain has a role in limiting this route of class II antigen presentation.
表达转染的DRA和DRB1*0101基因产物的人成纤维细胞系M1（M1-DR1）无法将完整的流感抗原呈递给一系列受DR1限制的人T细胞系和克隆，但完全能够呈递合成肽以供T细胞识别。相比之下，感染活流感病毒的M1-DR1细胞被两种多克隆血凝素或全病毒特异性T细胞系以及四个T细胞克隆中的一个所识别。这种差异不能简单地用感染性病毒克服M1-DR1细胞抗原摄取缺陷的能力来解释，因为内吞作用的直接研究表明，M1细胞在外源蛋白内化方面比人B细胞更有效。这些数据表明，M1细胞无法呈递外源性抗原，但能够用源自内源性抗原的肽加载主要组织相容性复合体（MHC）II类分子。为了进一步研究这一点，用编码人恒定链（Ii）的p33和p35形式的cDNA对M1-DR1细胞进行超级转染。通过转染子的胞内染色和代谢标记检测Ii链的表达。检测到等摩尔量的p33和p35形式，内质网中Ii蛋白的大量保留反映了p35 Ii的高水平。添加Ii链并没有恢复DR1对完整抗原的呈递，但抑制了活病毒的呈递。这些数据表明，M1-DR1细胞中的MHC II类分子可以用源自内源性蛋白质的肽加载，可能是在生物合成途径中，并且Ii链在限制II类抗原呈递的这条途径中起作用。
