Kageyama S, Tsomides T J, Fukusen N, Papayannopoulos I A, Eisen H N, Sykulev Y
Center for Cancer Research and Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
J Immunol. 2001 Mar 1;166(5):3028-34. doi: 10.4049/jimmunol.166.5.3028.
CTL clone 2C recognizes the allogeneic class I MHC molecule L(d) in association with peptides derived from alpha-ketoglutarate dehydrogenase (oxoglutarate dehydrogenase (OGDH)), a ubiquitous intracellular protein. One of these peptides, QLSPFPFDL (QL9), elicits more vigorous cytolytic responses than two previously identified naturally processed peptides with overlapping sequences, LSPFPFDL (p2Ca) and VAITRIEQLSPFPFDL (p2Cb), from OGDH. In this study, we show that QL9 forms a more stable complex with cell surface L(d) than does p2Ca or p2Cb and is processed from the longer, naturally occurring peptide p2Cb by 20S proteosomes in vitro. The N-terminal cyclized pyroglutaminyl QL9 (pyroQL9), a form of QL9 to which it is converted at the low pH used for peptide isolation from tissue extracts, is even more active than QL9 in cytotoxicity assays with 2C CTL. Overall, the results indicate that along with the abundant natural peptides p2Ca and p2Cb, the QL9 and other OGDH peptides of various lengths, sharing a conserved C-terminal sequence, are also processed and presented with L(d) as allogeneic ligands for T cells expressing 2C TCR. All these peptides, each available in a low amount, could act in concert at the cell surface, resulting in a high density of cognate ligands that accounts for the exceptionally potent cytolytic response by 2C CTL.
细胞毒性T淋巴细胞（CTL）克隆2C识别与源自α-酮戊二酸脱氢酶（氧代戊二酸脱氢酶，OGDH）（一种普遍存在的细胞内蛋白质）的肽相关联的同种异体I类主要组织相容性复合体（MHC）分子L(d)。这些肽中的一种，QLSPFPFDL（QL9），比之前鉴定的两种具有重叠序列的天然加工肽——来自OGDH的LSPFPFDL（p2Ca）和VAITRIEQLSPFPFDL（p2Cb），引发更强烈的细胞溶解反应。在本研究中，我们表明QL9与细胞表面L(d)形成的复合体比p2Ca或p2Cb更稳定，并且在体外由20S蛋白酶体从更长的天然存在的肽p2Cb加工而来。N端环化的焦谷氨酰基QL9（焦QL9），是QL9在从组织提取物中分离肽所使用的低pH条件下转化而成的一种形式，在与2C CTL进行的细胞毒性测定中比QL9更具活性。总体而言，结果表明，除了丰富的天然肽p2Ca和p2Cb之外，QL9和其他各种长度、共享保守C端序列的OGDH肽，也作为与L(d)结合的同种异体配体被加工并呈递给表达2C TCR的T细胞。所有这些肽，每种含量都很低，可能在细胞表面协同作用，导致同源配体的高密度，这解释了2C CTL异常强烈的细胞溶解反应。
