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标题：Self-mediated positive selection of T cells sets an obstacle to the recognition of nonself
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作者：Balázs Koncz ; Gergő M. Balogh ; Benjamin T. Papp 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2021
卷号：118
期号：37
DOI：10.1073/pnas.2100542118
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance It is well established that peptides that are dissimilar to human proteins are more immunogenic. However, the immune system is still unable to recognize a large fraction of highly dissimilar peptides found in a wide variety of pathogens. We propose that this phenomenon could be explained by the mechanism of T cell positive selection. During this process, only those cells survive that recognize human peptides on the surface of thymic epithelial cells. As self-peptides mediate positive selection, the immune system is unable to recognize many nonself peptides, most of which are highly dissimilar to human peptides. Adaptive immune recognition is mediated by the binding of peptide–human leukocyte antigen complexes by T cells. Positive selection of T cells in the thymus is a fundamental step in the generation of a responding T cell repertoire: only those T cells survive that recognize human peptides presented on the surface of cortical thymic epithelial cells. We propose that while this step is essential for optimal immune function, the process results in a defective T cell repertoire because it is mediated by self-peptides. To test our hypothesis, we focused on amino acid motifs of peptides in contact with T cell receptors. We found that motifs rarely or not found in the human proteome are unlikely to be recognized by the immune system just like the ones that are not expressed in cortical thymic epithelial cells or not presented on their surface. Peptides carrying such motifs were especially dissimilar to human proteins. Importantly, we present our main findings on two independent T cell activation datasets and directly demonstrate the absence of naïve T cells in the repertoire of healthy individuals. We also show that T cell cross-reactivity is unable to compensate for the absence of positively selected T cells. Additionally, we show that the proposed mechanism could influence the risk for different infectious diseases. In sum, our results suggest a side effect of T cell positive selection, which could explain the nonresponsiveness to many nonself peptides and could improve the understanding of adaptive immune recognition.
关键词：enadaptive immune recognition;T cell repertoire;infectious diseases;positive selection