Abstract
T cell receptors (TCRs) bind foreign or self-peptides attached to major histocompatibility complex (MHC) molecules, and the strength of this interaction determines T cell activation. Optimizing the ability of T cells to recognize a diversity of foreign peptides yet be tolerant of self-peptides is crucial for the adaptive immune system to properly function. This is achieved by selection of T cells in the thymus, where immature T cells expressing unique, stochastically generated TCRs interact with a large number of self-peptide-MHC; if a TCR does not bind strongly enough to any self-peptide-MHC, or too strongly with at least one self-peptide-MHC, the T cell dies. Past theoretical work cast thymic selection as an extreme value problem and characterized the statistical enrichment or depletion of amino acids in the postselection TCR repertoire, showing how T cells are selected to be able to specifically recognize peptides derived from diverse pathogens yet have limited self-reactivity. Here, we investigate how the diversity of the postselection TCR repertoire is modified when TCRs make nonuniform contacts with peptide-MHC. Specifically, we were motivated by recent experiments showing that amino acids at certain positions of a TCR sequence have large effects on thymic selection outcomes, and crystal structure data that reveal a nonuniform contact profile between a TCR and its peptide-MHC ligand. Using a representative TCR contact profile as an illustration, we show via simulations that the statistical enrichment or depletion of amino acids now varies by position according to the contact profile, and, importantly, it depends on the implementation of nonuniform contacts during thymic selection. We explain these nontrivial results analytically. Our study has implications for understanding the selection forces that shape the functionality of the postselection TCR repertoire.
Original language | English |
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Article number | 032413 |
Journal | Physical Review E |
Volume | 97 |
Issue number | 3 |
DOIs | |
State | Published - 22 Mar 2018 |
Externally published | Yes |
Bibliographical note
Publisher Copyright:© 2018 American Physical Society.
Funding
This work was supported by the Ragon Institute of MGH, MIT and Harvard and an A∗STAR Scholarship (to H.C.). M.K. acknowledges support from NSF through grant number DMR-1708280. This work was supported by the Ragon Institute of MGH, MIT and Harvard and an A*STAR Scholarship (to H.C.). M.K. acknowledges support from NSF through grant number DMR-1708280.
Funders | Funder number |
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Ragon Institute of MGH | |
National Science Foundation | DMR-1708280 |
Directorate for Mathematical and Physical Sciences | 1708280 |
Massachusetts Institute of Technology | |
Harvard University | |
Agency for Science, Technology and Research | |
Norsk Sykepleierforbund |