Avishai Mimran

Tregs in T cell vaccination: exploring the regulation of regulation

T cell vaccination (TCV) activates Tregs of 2 kinds: anti-idiotypic (anti-id) and anti-ergotypic (anti-erg). These regulators furnish a useful view of the physiology of T cell regulation of the immune response. Anti-id Tregs recognize specific effector clones by their unique TCR CDR3 peptides; anti-id networks of CD4+ and CD8+ Tregs have been described in detail. Here we shall focus on anti-erg T regulators. Anti-erg T cells, unlike anti-id T cells, do not recognize the clonal identity of effector T cells; rather, anti-erg T cells recognize the state of activation of target effector T cells, irrespective of their TCR specificity. We consider several features of anti-erg T cells: their ontogeny, subset markers, and target ergotope molecules; mechanisms by which they regulate other T cells; mechanisms by which they get regulated; and therapeutic prospects for anti-erg upregulation and downregulation.

DNA vaccination with CD25 protects rats from adjuvant arthritis and induces an antiergotypic response

Abs to the alpha-chain of the IL-2 receptor (anti-CD25) are used clinically to achieve immunosuppression. Here we investigated the effects of DNA vaccination with the whole CD25 gene on the induction of rat adjuvant arthritis. The DNA vaccine protected the rats and led to a shift in the cytokine profile of T cells responding to disease target antigens from Th1 to Th2. The mechanism of protection was found to involve the induction of an antiergotypic response, rather than the induction of anti-CD25 Abs. Antiergotypic T cells respond to activation molecules, ergotopes, expressed on syngeneic activated, but not resting, T cells. CD25-derived peptides function as ergotopes that can be recognized by the antiergotypic T cells. Antiergotypic T cells taken from control sick rats did not proliferate against activated T cells and secreted mainly IFN-gamma. In contrast, antiergotypic cells from CD25-DNA-protected rats proliferated against activated T cells and secreted mainly IL-10. Protective antiergotypic T cells were found in both the CD4+ and CD8+ populations and expressed alpha/beta or gamma/delta T cell receptors. Antiergotypic alpha/beta T cells were MHC restricted, while gamma/delta T cells were MHC independent. Thus, CD25 DNA vaccination may induce protection from autoimmunity by inducing a cytokine shift in both the antiergotypic response and the response to the antigens targeted in the disease.

Autoimmune Encephalomyelitis and Uveitis Induced by T Cell Immunity to Self β-Synuclein

β-synuclein is a neuronal protein that accumulates in the plaques that characterize neurodegenerative diseases such as Parkinson’s and Alzheimer’s diseases. It has been proposed that immunization to peptides of plaque-forming proteins might be used therapeutically to help dissociate pathogenic plaques in the brain. We now report that immunization of Lewis rats with a peptide from β-synuclein resulted in acute paralytic encephalomyelitis and uveitis. T cell lines and clones reactive to the peptide adoptively transferred the disease to naive rats. Immunoblotting revealed the presence of β-synuclein in heavy myelin, indicating that the expression of β-synuclein is not confined to neurons. These results add β-synuclein to the roster of encephalitogenic self Ags, point out the potential danger of therapeutic autoimmunization to β-synuclein, and alert us to the unsuspected possibility that autoimmunity to β-synuclein might play an inflammatory role in the pathogenesis of neurodegeneration.

HSP60 as a Target of Anti-Ergotypic Regulatory T Cells

The 60 kDa heat shock protein (HSP60) has been reported to influence T-cell responses in two ways: as a ligand of toll-like receptor 2 signalling and as an antigen. Here we describe a new mechanism of T-cell immuno-regulation focused on HSP60: HSP60 is up-regulated and presented by activated T cells (HSP60 is an ergotope) to regulatory (anti-ergotypic) T cells. Presentation of HSP60 by activated T cells was found to be MHC-restricted and dependent on accessory molecules - CD28, CD80 and CD86. Anti-ergotypic T cells responded to T-cell HSP60 by proliferation and secreted IFNγ and TGFβ1. In vitro, the anti-ergotypic T cells inhibited IFNγ production by their activated T-cell targets. In vivo, adoptive transfer of an anti-ergotypic HSP60-specific T-cell line led to decreased secretion of IFNγ by arthritogenic T cells and ameliorated adjuvant arthritis (AA). Thus, the presentation of HSP60 by activated T cells turns them into targets for anti-ergotypic regulatory T cells specific for HSP60. However, the direct interaction between the anti-ergotypic T regulators (anti-HSP60) and the activated T cells also down-regulated the regulators. Thus, by functioning as an ergotope, HSP60 can control both the effector T cells and the regulatory HSP60-specific T cells that control them.

Systemic lupus erythematosus in mice, spontaneous and induced, is associated with autoimmunity to the C-terminal domain of p53 that recognizes damaged DNA.

The tumor suppressor molecule p53 features a regulatory domain at the C terminus that recognizes damaged DNA. Since damaged DNA might be involved in activating anti‐DNA autoantibodies, we tested whether autoimmunity to the C terminus of p53 might mark murine systemic lupus erythematosus (SLE). We now report that MRL / MpJ‐Faslpr mice, which spontaneously develop SLE, produce antibodies both to the C terminus of p53 and to a monoclonal antibody (PAb‐421) that binds the p53 C terminus. Anti‐idiotypic antibodies to PAb‐421 (sampled as monoclonal antibodies) could also bind DNA. Thus, the PAb‐421 antibody mimics DNA, and the anti‐idiotypic antibody to PAb‐421 mimics the p53 DNA‐binding site. This mimicry was functional; immunization of BALB / c mice to PAb‐421 induced anti‐DNA antibodies and antibodies to the C terminus of p53, and most of the mice developed an SLE‐like disease. Immunization of C57BL / 6 mice to PAb‐421 induced antibodies to p53, but not to its C‐terminal domain. The C57BL / 6 mice also did not develop anti‐DNA antibodies or the SLE‐like disease. Thus, network autoimmunity to the domain of p53 that recognizes damaged DNA can be a pathogenic feature in SLE in genetically susceptible strains of mice.

Regulatory T Cells in Autoimmune Diseases: Anti-Ergotypic T Cells

T regulatory cells play an important role in regulating T-cell responses to self-antigens and control autoimmunity and autoimmune disease. Anti-ergotypic T cells are a subset of such regulatory T cells that respond to activation markers, ergotopes, expressed on other activated T cells. Anti-ergotypic T cells do not respond to nonactivated T cells. Ergotopes include the α-chain of the IL-2 receptor (CD25). Anti-ergotypic T cells were found to downregulate experimental diseases such as experimental autoimmune encephalomyelitis (EAE) and adjuvant arthritis (AA). Anti-ergotypic T cells are present in humans and are activated after T-cell vaccination. Here we review anti-ergotypic T cells in animal models and in humans and contrast anti-ergotypic T cells with other regulatory T-cell subsets.

Monoclonal antibody to a DNA-binding domain of p53 mimics charge structure of DNA: anti-idiotypes to the anti-p53 antibody are anti-DNA

Antibodies to DNA are important markers of various autoimmune diseases and can be pathogenic; however, their generation is not understood. We previously reported that anti‐DNA antibodies could be induced in mice by idiotypic immunization to PAb‐421, an antibody to a DNA‐binding domain of p53. We now report that two monoclonal antibodies of moderate affinity (KD≈︁10–7), raised from PAb‐421‐immunized mice, specifically recognized both PAb‐421 and DNA. These antibodies feature multiple arginine residues in the antigen‐binding site, a unique characteristic of disease‐associated anti‐DNA antibodies; nevertheless, these anti‐DNA antibodies show specific complementarity to PAb‐421 by competing with p53 for PAb‐421 binding and recognize defined oligonucleotides with a specificity similar to that of p53. To study the structural basis for the cross‐recognition of PAb‐421 and DNA by the anti‐DNA antibodies, we constructed computer models (fine‐tuned by protein‐protein docking) of PAb‐421 and one of the monoclonal anti‐DNA antibodies. The modeled structures manifested structural complementarity. Most notably, the modeled structure of PAb‐421 resembled the structure of DNA by the positions of negatively charged groups and aromatic side chains. Thus, a protein molecule may mimic the structure of DNA and the elusive generation of anti‐DNA antibodies could be explained by idiotypic immunity to a DNA‐binding protein, like p53.