Autoimmune disease and T-cell immunologic recognition

The mouse (Mus musculus) T cell receptor alpha (TRA) and delta (TRD) variable genes

'The Mouse (Mus musculus) T cell receptor alpha (TRA) and delta (TRD) variable genes' 'IMGT Locus in Focus' report provides the first complete list of the mouse TRAV and TRDV genes which span 1550 kb on chromosome 14 at 19.7 cM. The total number of TRAV genes per haploid genome is 98 belonging to 23 subgroups. This includes 10 TRAV/DV genes which belong to seven subgroups. The functional TRAV genomic repertoire comprises 72-82 TRAV (including 9-10 TRAV/DV) belonging to 19 subgroups. The total number of TRDV genes per haploid genome is 16 (including the 10 TRAV/DV) belonging to 12 subgroups. The functional TRDV genomic repertoire comprises 14-15 genes (5 TRDV and 9-10 TRAV/DV) belonging to 11-12 subgroups. The eight tables and three figures of this report are available at the IMGT Marie-Paule page of IMGT. The international ImMunoGeneTics information system (http://imgt.cines.fr) created by Marie-Paule Lefranc, Université Montpellier II, CNRS, France.

Autoimmunity and neurological disease: antibody modulation of synaptic transmission

Over the past three decades, compelling evidence has emerged that the immune system can attack the nervous system with devastating consequences for human health. Either cell-mediated or humoral (antibody-mediated) autoimmune mechanisms may predominate in effecting a given disease, and either glia or neurons may fall under immune attack. A subset of these diseases has been particularly useful for understanding fundamental neuroscience as well as mechanisms of human disease. This subset involves humoral autoimmune attack on cell surface molecules subserving transmembrane signaling of excitable cells; special emphasis is placed here on proteins involved in synaptic transmission. We begin by reviewing the prototypic humoral autoimmune disease of synaptic transmission, myasthenia gravis. This provides a context for insights obtained from the study of diseases targeting molecules that regulate synaptic transmission at the neuromuscular junction and in the central nervous system. We also explore a disease where autoimmunity produces agonist antibodies acting at two distinct G-protein-coupled receptors. We conclude with an exploration of the vital issue of access of antibodies to targets within the central nervous system and the implications that such access may have in the pathogenesis of poorly understood idiopathic central nervous system diseases.

Shifting T-cell activation thresholds in autoimmunity and determinant spreading

The best-characterized autoimmune T-cell response is that to myelin basic protein (MBP). MBP has classically been regarded as a sequestered antigen that does not cause negative selection. This view has been fostered by the observation that T-cell receptor-transgenic T cells that are specific for the "immunodominant determinant" on the molecule, MBP:Ac1-11, persist as naive cells in MBP-expressing H-2u mice. The same T cells, however, can cause autoimmune pathology once they have been primed by environmental stimulation to become memory cells. Once the autoimmune response to Ac1-11 has been engaged, determinant spreading occurs and second-wave T-cell responses that are specific for weaker, "cryptic" determinants like MBP:121-140 develop. Although the nature of these cryptic determinants has been enigmatic, recent studies using MBP-/- mice have provided new insights. These studies showed that MBP is not a sequestered antigen, but one that causes negative selection; as MBP:121-140 is actually the immunodominant determinant in MBP-/- mice, it tolerizes high avidity clones in MBP+/+ mice, making it appear cryptic. Based on this new information, we attempt here to redefine the MBP-specific repertoire within the theoretical framework of the threshold model for negative selection, and we propose a model of shifting T-cell activation thresholds to explain how ignorant/naive T cells can become effector cells of autoimmune pathology and why this effector cell repertoire spreads.

Major histocompatibility complex binding affinity of an antigenic determinant is crucial for the differential secretion of interleukin 4/5 or interferon gamma by T cells

Differential activation of CD4+ T-cell precursors in vivo leads to the development of effectors with unique patterns of lymphokine secretion. To investigate whether the differential pattern of lymphokine secretion is influenced by factors associated with either the display and/or recognition of the ligand, we have used a set of ligands with various class II binding affinities but unchanged T-cell specificity. The ligand that exhibited approximately 10,000-fold higher binding to I-Au considerably increased the frequency of interferon gamma-producing but not interleukin (IL) 4- or IL-5-secreting cells in vivo. Using an established ligand-specific, CD4+ T-cell clone secreting only IL-4, we also demonstrated that stimulation with the highest affinity ligand resulted in interferon gamma production in vitro. In contrast, ligands that demonstrated relatively lower class II binding induced only IL-4 secretion. These data suggest that the major histocompatibility complex binding affinity of antigenic determinants, leading to differential interactions at the T cell-antigen-presenting cell interface, can be crucial for the differential development of cytokine patterns in T cells.

Holes in the T cell repertoire to myelin basic protein owing to the absence of the D beta 2-J beta 2 gene cluster: implications for T cell receptor recognition and autoimmunity

Models of T cell recognition suggest that amino acid residues in the CDR3 region of the T cell receptor (TCR) alpha or beta chain directly contact the major histocompatibility complex-bound peptide, and thus are crucial for providing peptide specificity. T cells derived from B10.PL or PL/J mice of H-2u haplotype, use only D beta 2 and J beta 2 gene segments in the recognition of the dominant determinant, Ac1-9/Au, of myelin basic protein (MBP). New Zealand White (NZW) mice, with identical class II H-2u genes (I-A and I-E), carry an 8.8-kb deletion in their TCR beta chain locus encompassing D beta 2 and J beta 2 gene segments. How does this deletion of the crucial D beta 2-J beta 2 region in NZW mice influence specific responses to Ac1-9/Au as well as to other known Au or Eu determinants of MBP? We found that these mice respond very poorly to the dominant Ac1-9/Au and to the subdominant 31-50/Eu determinant in in vitro proliferation assays as well as in their in vivo capacity to induce experimental autoimmune encephalomyelitis. This loss of response is apparently owing to the absence of high avidity TCRs with essential CDR3 residues contributed by D beta 2 or J beta 2 gene segments. These data reveal constraints in the recognition of certain antigenic structures, and further support a TCR-recognition model in which CDR3 residues of the TCR alpha and beta chains constitute the antigenic peptide-binding sites on the TCR molecule. Implications for autoimmune manifestations contributed by NZW genes in (NZB x NZW)F1 disease are also discussed.

Spreading of T-cell autoimmunity to cryptic determinants of an autoantigen

Immunization with myelin basic protein (MBP) induces experimental allergic encephalomyelitis (EAE), a prototype of CD4+ T-cell mediated autoimmune disease. In rodents, MBP-reactive T-cell clones are specific for a single, dominant determinant on MBP and use a highly restricted number of T-cell receptor genes. Accordingly, EAE has been prevented by various receptor-specific treatments, suggesting similar strategies may be useful for therapy of human autoimmune disease. Here we report that in (SJL x B10.PL)F1 mice, immune dominance of a single determinant, MBP:Ac1-11, is confined to the inductive phase of EAE. In mice with chronic EAE, several additional determinants of MBP in peptides 35-47, 81-100 and 121-140 recall proliferative responses. Most importantly, reactivity to the latter determinants was also detected after induction of EAE with MBP peptide Ac1-11 alone; this demonstrates priming by endogenous MBP determinants. Thus, determinants of MBP that are cryptic after primary immunization can become immunogenic in the course of EAE. Diversification of the autoreactive T-cell repertoire due to 'determinant spreading' has major implications for the pathogenesis of, and the therapeutic approach to, T-cell driven autoimmune disease.

Assessment of antigenic determinants for the human T cell response against myelin basic protein using overlapping synthetic peptides

Immunization of experimental animals with myelin basic protein (MBP) or with specific MBP encephalitogenic determinants induces an autoimmune central nervous system (CNS) disease, experimental allergic encephalomyelitis, often studied as a model for human demyelinating disorders. This study examines the antigenic determinants of MBP recognized by human T cells using overlapping, synthetic peptides and T cell lines and clones isolated from four HLA-typed, neurologically normal subjects. T cell lines and clones isolated from individual subjects recognized at least one and as many as five distinct T cell determinants. In some instances the peptides recognized included determinants previously shown to induce experimental allergic encephalomyelitis (EAE) in experimental animals. In this group of four subjects, some determinants of MBP, including residues 5-25, 35-47, 65-75, and 81-100, were recognized by T cells derived from more than one individual suggesting that these regions may be particularly immunogenic for humans.