ABSTRACT
The T-cell receptor (TCR) is a highly polymorphic surface receptor that allows T-cells to recognize antigenic peptides presented on the major histocompatibility complex (MHC). Changes in the TCR repertoire have been observed in several autoimmune conditions, and these changes are suggested to predispose autoimmunity. Multiple lines of evidence have implied an important role for T-cells in the pathogenesis of Systemic Sclerosis (SSc), a complex autoimmune disease. One of the major questions regarding the roles of T-cells is whether expansion and activation of T-cells observed in the diseases pathogenesis is antigen driven. To investigate the temporal TCR repertoire dynamics in SSc, we performed high-throughput sequencing of CD4+ and CD8+ TCRß chains on longitudinal samples obtained from four SSc patients collected over a minimum of two years. Repertoire overlap analysis revealed that samples taken from the same individual over time shared a high number of TCRß sequences, indicating a clear temporal persistence of the TCRß repertoire in CD4+ as well as CD8+ T-cells. Moreover, the TCRßs that were found with a high frequency at one time point were also found with a high frequency at the other time points (even after almost four years), showing that frequencies of dominant TCRßs are largely consistent over time. We also show that TCRß generation probability and observed TCR frequency are not related in SSc samples, showing that clonal expansion and persistence of TCRßs is caused by antigenic selection rather than convergent recombination. Moreover, we demonstrate that TCRß diversity is lower in CD4+ and CD8+ T-cells from SSc patients compared with memory T-cells from healthy individuals, as SSc TCRß repertoires are largely dominated by clonally expanded persistent TCRß sequences. Lastly, using "Grouping of Lymphocyte Interactions by Paratope Hotspots" (GLIPH2), we identify clusters of TCRß sequences with homologous sequences that potentially recognize the same antigens and contain TCRßs that are persist in SSc patients. In conclusion, our results show that CD4+ and CD8+ T-cells are highly persistent in SSc patients over time, and this persistence is likely a result from antigenic selection. Moreover, persistent TCRs form high similarity clusters with other (non-)persistent sequences that potentially recognize the same epitopes. These data provide evidence for an antigen driven expansion of CD4+/CD8+ T-cells in SSc.
Subject(s)
CD4-Positive T-Lymphocytes/immunology , CD4-Positive T-Lymphocytes/metabolism , CD8-Positive T-Lymphocytes/immunology , CD8-Positive T-Lymphocytes/metabolism , Receptors, Antigen, T-Cell/genetics , Scleroderma, Systemic/etiology , Scleroderma, Systemic/metabolism , Adult , Antigens/immunology , Disease Susceptibility , Epitopes , Female , Gene Frequency , High-Throughput Nucleotide Sequencing , Humans , Immunologic Memory , Immunophenotyping , Longitudinal Studies , Lymphocyte Activation , Male , Middle Aged , Receptors, Antigen, T-Cell/metabolism , Receptors, Antigen, T-Cell, alpha-beta/genetics , Receptors, Antigen, T-Cell, alpha-beta/metabolism , Scleroderma, Systemic/pathologyABSTRACT
Systemic sclerosis (SSc) is a complex, heterogeneous autoimmune connective tissue disease. Autologous hematopoietic stem-cell transplantation (AHSCT) has emerged as a valuable treatment option for rapidly progressive diffuse cutaneous SSc (dcSSc) patients, and thus far is the only treatment that has been shown to have a long-term clinical benefit. AHSCT is thought to reintroduce immune homeostasis through elimination of pathogenic self-reactive immune cells and reconstitution of a new, tolerant immune system. However, the mechanism of action underlying this reset to tolerance remains largely unknown. In this study we review the immune mechanisms underlying AHSCT for SSc, with a focus on the role of the innate immune cells, including monocytes and natural killer (NK) cells, in restoring immune balance after AHSCT.
