A public T cell clonotype within a heterogeneous autoreactive repertoire is dominant in driving EAE.

Experimental autoimmune encephalomyelitis (EAE) is an animal model of multiple sclerosis. Immunization of B10.PL mice with the Ac1-9 peptide, the immunodominant determinant of myelin basic protein (MBP), produced a single episode of EAE followed by recovery and resistance to reinduction of disease. Using the CDR3 length spectratyping technique, we characterized the clonal composition of the Ac1-9-specific T cell repertoire from induction through onset and resolution of disease. Two clonally restricted subsets within a heterogeneous self-reactive repertoire were found in mouse lymph nodes, spleen, and spinal cord soon after immunization, before any sign of EAE. These clonotypes, designated BV8S2/BJ2S7 and BV16/BJ2S5, were present in all mice examined and thus considered public. BV8S2/BJ2S7 was found in far greater excess; was exclusively Th1 polarized; disappeared from the spinal cord, spleen, and lymph nodes concomitantly with recovery; and transferred disease to naive recipients. In contrast, BV16/BJ2S5 and numerous private clonotypes were either Th1 or Th2 and persisted following recovery. These results are consistent with the hypothesis that the public clonotype BV8S2/BJ2S7 is a driver of disease and necessary for its propagation.

TAP1-/- mice present oligoclonal BV-BJ expansions following the rejection of grafts bearing self antigens.

Our previous work showed that transporter associated with antigen processing 1 (TAP1)-/- (H-2b) mice rejected grafts from H-2b mice which display a normal density of class I major histocompatibility complex (MHC) molecules at the cell surface. Our results indicated that H-2b molecules themselves may be a target in this kind of rejection and that CD4+ T cells play a major role in this autoreactive process. Our data also suggested that TAP1-/- mice, in addition to the well-recognized phenotype of class I and CD8+ T-cell deficiency, present a functional alteration in their autoreactive CD4+ T-cell repertoires. In this model of inflammatory autoreactivity to modified self, we have analysed T-cell receptor (TCR) V-beta-J-beta (BV-BJ) usage by complementarity determining region 3 (CDR3) length spectratyping in splenocytes from naïve TAP1-/- mice and transplanted TAP1-/- mice that rejected B6 heart grafts or responded to synthetic self H-2Kb peptides. Importantly, oligoclonal T-cell expansions shared by different animals were detected in the peripheral T-cell repertoire of transplanted TAP1-/- mice. Such public expansions were also induced in vitro by H-2Kb peptides, suggesting that dominant class I peptides can induce preferential expansions of restricted T-cell populations during rejection. Some of these public T-cell expansions were also detected in transplanted mice even before in vitro stimulation with peptides, indicating that post-transplantation expansion of these populations had occurred in vivo. The functional activity of these T-cell populations awaits elucidation, as do the underlying mechanisms involved in the inflammatory autoreactive process, in TAP1-/- mice.

T cells to a dominant epitope of GAD65 express a public CDR3 motif.

Non-obese diabetic (NOD) mice spontaneously develop autoimmune diabetes, and serve as a model for type 1 diabetes (T1D) and natural autoimmunity. T cell responses to the pancreatic islet antigen glutamic acid decarboxylase 65 (GAD65) can be detected in the spleens of young prediabetic NOD mice, which display a unique MHC class II molecule. Here, we report that a distinct TcR beta chain and CDR3 motif are utilized by all NOD mice in response to a dominant determinant on GAD65, establishing a public repertoire in the spontaneous autoimmunity to an important islet cell antigen. GAD65 530-543 (p530)-reactive T cells preferentially utilize the Vbeta4, Dbeta2.1 and Jbeta2.7 gene segments, with a CDR3 that is characterized by a triad of amino acids, DWG, preceded by a polar residue. In addition, we used CDR3 length spectratyping, CDR3-specific reverse transcriptase-PCR and direct TcR sequencing to show that the TcR beta chain structural patterns associated with p530-specific T cells consistently appeared in the islets of young NOD mice with insulitis, but not in the inflamed islets of streptozotocin-treated C57BL/6 mice, or in inflamed NOD salivary glands. To our knowledge, this is the first report to demonstrate that a public T cell repertoire is used in spontaneous autoimmunity to a dominant self-determinant. These findings suggest that defined clonotypes and repertoires may be preferentially selected in haplotypes predisposed to spontaneous autoimmunity.

Preferential escape of subdominant CD8+ T cells during negative selection results in an altered antiviral T cell hierarchy.

Negative selection is designed to purge the immune system of high-avidity, self-reactive T cells and thereby protect the host from overt autoimmunity. In this in vivo viral infection model, we show that there is a previously unappreciated dichotomy involved in negative selection in which high-avidity CD8(+) T cells specific for a dominant epitope are eliminated, whereas T cells specific for a subdominant epitope on the same protein preferentially escape deletion. Although this resulted in significant skewing of immunodominance and a substantial depletion of the most promiscuous T cells, thymic and/or peripheral deletion of high-avidity CD8(+) T cells was not accompanied by any major change in the TCR V beta gene family usage or an absolute deletion of a single preferred complementarity-determining region 3 length polymorphism. This suggests that negative selection allows high-avidity CD8(+) T cells specific for subdominant or cryptic epitopes to persist while effectively deleting high-avidity T cells specific for dominant epitopes. By allowing the escape of subdominant T cells, this process still preserves a relatively broad peripheral TCR repertoire that can actively participate in antiviral and/or autoreactive immune responses.