A myelin basic protein peptide is recognized by cytotoxic T cells in the context of four HLA-DR types associated with multiple sclerosis

Detection of skewed T-cell receptor V-beta gene usage in the peripheral blood of patients with multiple sclerosis

The ex vivo analysis of the T-cell receptor V-beta (TCRBV) gene usage by circulating T lymphocytes in Multiple Sclerosis (MS) patients may contribute to understanding disease pathogenesis. In the present study, TCRBV gene usage was analyzed in freshly collected unstimulated peripheral blood mononuclear cells (PBMC) isolated from 40 MS patients and 20 healthy controls. Nine patients presented abnormal repertoires, with expansion of one or more TCRBV segments. Among these patients, six presented expansion of TCRBV9 chain expression, three also having an expansion of TCRBV1, TCRBV11 and TCRBV22 segments. The most frequently observed TCRBV chain expansion, TCRBV9, was further analyzed and identified as polyclonal. Evaluation of clinical variables showed that median disease duration was shorter in patients with TCRBV gene expression abnormalities. Longitudinal evaluation of five patients with a skewed repertoire showed regression of expanded TCRBV chains expression to normal values. These data indicate that certain MS patients have abnormal TCRBV gene expression. Such abnormalities are caused by polyclonal expansions of T lymphocyte subpopulations that use the same TCRBV gene families, are unstable and preferentially observed early in the course of the disease.

Several Common HLA-DR Types Share Largely Overlapping Peptide Binding Repertoires

The peptide binding specificities of HLA-DRB1*0401, DRB1*0101, and DRB1*0701 have been analyzed by the use of large collections of synthetic peptides corresponding to naturally occurring sequences. The results demonstrated that nearly all peptides binding to these DR molecules bear a motif characterized by a large aromatic or hydrophobic residue in position 1 (Y, F, W, L, I, V, M) and a small, noncharged residue in position 6 (S, T, C, A, P, V, I, L, M). In addition, allele-specific secondary effects and secondary anchors were defined, and these parameters were utilized to derive allele-specific motifs and algorithms. By the combined use of such algorithms, peptides capable of degenerate DRB1*0101, DRB1*0401, and DRB1*0701 binding were identified. Additional experiments utilizing a panel of quantitative assays specific for nine additional common DR molecules identified a large set of DR molecules, which includes at least the DRB1*0101, DRB1*0401, DRB1*0701, DRB5*0101, DRB1*1501, DRB1*0901, and DRB1*1302 allelic products, characterized by overlapping peptide-binding repertoires. These results have implications for understanding the molecular interactions involved in peptide-DR binding, as well as the genetic and structural basis of MHC polymorphism. These results also have potential practical implications for the development of epitope-based prophylactic and therapeutic vaccines.

Lack of over-expression of T cell receptor Vbeta5.2 in myelin basic protein-specific T cell lines derived from HLA-DR2 positive multiple sclerosis patients and controls

Based on studies reporting an overexpression of certain V genes in myelin basic protein (MBP)-specific T cells from MS patients, immunotherapies targeting single TCR (Vbeta5.2, Vbeta6.1) are currently under way. In order to assess the basic assumption for one of these therapeutic strategies, i.e. the overexpression of Vbeta5.2 by MBP-specific T cells, we analyzed 100 MBP-specific T cell lines (TCL) for Vbeta5.2 expression. Only 4 out of 100 TCL expressed Vbeta5.2, and expression of this TCR gene is therefore not more frequent than expected from the normal peripheral blood distribution.

Expansion of Autoreactive T Cells in Multiple Sclerosis Is Independent of Exogenous B7 Costimulation

Multiple sclerosis (MS) is an inflammatory disease of the myelinated central nervous system that is postulated to be induced by myelin-reactive CD4 T cells. T cell activation requires an antigen-specific signal through the TCR and a costimulatory signal, which can be mediated by B7–1 or B7–2 engagement of CD28. To directly examine the activation state of myelin-reactive T cells in MS, the costimulation requirements necessary to activate myelin basic protein (MBP) or tetanus toxoid (TT)-reactive CD4 T cells were compared between normal controls and MS patients. Peripheral blood T cells were stimulated with Chinese hamster ovary (CHO) cells transfected either with DRB1*1501/DRA0101 chains (t-DR2) alone, or in combination with, B7–1 or B7–2. In the absence of costimulation, T cells from normal subjects stimulated with the recall antigen TT p830–843 were induced to expand and proliferate, but stimulation with MBP p85–99 did not have this effect. In marked contrast, T cells from patients with MS stimulated with MBP p85–99 in the absence of B7–1 or B7–2 signals expanded and proliferated. Thus, MBP-reactive CD4 T cells in patients with MS are costimulation independent and have been previously activated in vivo. These experiments provide further direct evidence for a role of activated MBP-specific CD4 T cells in the pathogenesis of MS.

Insights into the aetiology and pathogenesis of multiple sclerosis

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system, and the most common neurological disease affecting young adults. Multiple sclerosis is a clinically heterogeneous disorder. It is believed to be an autoimmune disease, with cell-mediated and humoral responses directed against myelin proteins. This hypothesis largely comes from pathological parallels with an animal model, experimental autoimmune encephalomyelitis (EAE). Autoimmunity to myelin proteins in humans may be inadvertently triggered by microbes which have structural homologies with myelin antigens (molecular mimicry). As with other autoimmune diseases, susceptibility to MS is associated with certain MHC genes/haplotypes. Full genomic screening of mutiplex families has underscored the role for MHC genes as exerting moderate but the most significant effects in susceptibility. The primary target autoantigen in MS has yet to be definitively identified, but as well as the major myelin proteins, it is now clear that minor myelin components, such as myelin oligodendrocyte glycoprotein (MOG) may play a primary role in disease initiation. This review examines the current knowledge about the aetiology and pathogenesis of MS, and the important similarities with EAE. A better understanding of the molecular mechanisms of autoimmune pathology will provide the basis for more rational immunotherapies to treat MS.

T cell receptor clonotypes in skin lesions from patients with systemic lupus erythematosus

Systemic lupus erythematosus is an autoimmune disease characterized by the presence of autoantibodies and by lymphocytic infiltration into lesions at several sites such as skin, kidney, and other organs. Immunohistologic studies have clarified that the majority of lymphocytes in the skin are CD4+ alphabeta T cells. In the present work, to clarify the pathologic role of T cells in the skin of systemic lupus erythematosus patients, we analyzed T cell receptor (TCR) clonotypes of T cells infiltrating into skin lesions. TCR Vbeta gene transcripts from T cells from discoid lesions of the skin and peripheral blood lymphocytes of four systemic lupus erythematosus patients were amplified by reverse transcriptase polymerase chain reaction. Southern blot analysis of polymerase chain reaction product demonstrated the heterogeneous TCR Vbeta repertoire of T cells in the skin of systemic lupus erythematosus. Single-strand conformation polymorphism analysis showed several distinct bands for smears of most TCR Vbeta genes from T cells infiltrating the skin, whereas smears with few bands were found for all TCR Vbeta genes from peripheral blood lymphocytes of the same patients. The number of bands encoding each TCR Vbeta gene from the skin was significantly higher compared with peripheral blood lymphocytes. Sequencing analysis showed a Leucine-X-Glycine amino acid motif at position 96-98 in the CDR3 region at the frequency of 23-24% in skin-accumulated T cells from two patients, whereas the frequency of this motif in peripheral T cells was only 0-3%, indicating limited T cell epitopes. In conclusion, T cells infiltrating into the skin of systemic lupus erythematosus patients might recognize restricted T cell epitopes on autoantigens and trigger the autoimmune reaction in skin lesions.

Tolerance induction to myelin basic protein by intravenous synthetic peptides containing epitope P85 VVHFFKNIVTP96 in chronic progressive multiple sclerosis

Peptide-based tolerance induction may be useful for antigen-specific immunotherapy of human autoimmune diseases. Induction of tolerance to myelin basic protein (MBP) was examined in a Phase I clinical trial in multiple sclerosis (MS) patients with chronic progressive disease using a peptide that is immunodominant for MBP specific T cells and B cells. Tolerance induction was monitored by quantification of MBP specific autoantibodies in cerebrospinal fluid (CSF). The route of peptide administration was important since only intravenous but not intrathecal or subcutaneous injection induced tolerance to MBP. Following a single intravenous injection of a peptide containing epitope P85VVHFFKNIVTP96, MBP autoantibodies were undetectable for three to four months. Tolerance was more prolonged following a second injection since autoantibodies were low or undetectable after one year in the majority of patients. Duration of tolerance to MBP depended on MHC class II haplotypes of patients; tolerance was long-lived in all patients with disease associated HLA-DR2. No neurological or systemic side effects were observed, regardless of the route of peptide administration. These data demonstrate that intravenous administration of a soluble peptide can result in long-lasting tolerance to an autoantigen in humans.

Identification of multiple sclerosis-associated genes

Multiple sclerosis (MS) is a complex genetic trait. Analyses to identify genetic variants that increase susceptibility to MS have primarily focused on candidate genes, either in family linkage investigations or in association (linkage disequilibrium) studies in sporadic cases and control subjects. Most of the candidate genes considered to date either influence immune function or encode structural myelin proteins. Recently, three preliminary whole genomic surveys were completed, and they reveal multiple loci of possible genetic linkage that are worthy of further study. No convincing evidence for a single strong locus has emerged from analysis of the three studies. Linkage promises to focus the future choice of candidate genes for further investigation.

Interstrain variability of autoimmune encephalomyelitis in rats: multiple encephalitogenic myelin basic protein epitopes for DA rats

We investigated T cell epitopes of guinea pig myelin basic protein (MBP) that induce experimental autoimmune encephalomyelitis (EAE) in DA rats, using synthetic peptides that correspond to regions of the guinea pig MBP molecule that are homologous to rat MBP. Four peptides were encephalitogenic when tested in DA rats. MBP63-81, which partially overlaps the dominant encephalitogenic MBP epitope for Lewis (LEW) rats, caused severe EAE in the DA strain but did not elicit EAE in LEW rats. MBP66-81 and MBP63-76 were also encephalitogenic for DA but not LEW rats. MBP79-99 also induced EAE in DA rats, although MBP87-99, the minor encephalitogenic LEW epitope, was inactive. This indicates that part of the 79-86 sequence is necessary for encephalitogenic activity in the DA strain. MBP101-120, and MBP142-167 were also encephalitogenic for DA rats. T cells from DA rats immunized with intact MBP proliferated in response to the whole protein and to MBP79-99, but were not stimulated to a significant extent by the other encephalitogenic peptides, suggesting that these may represent cryptic or subdominant epitopes. However, MBP63-81-specific T cell lines could be isolated by repeated restimulation with peptide, indicating that the peptide-specific T cells were present in DA rats at low frequency.

Longitudinal study of myelin basic protein-specific T-cell receptors during the course of multiple sclerosis

This study analyzed the stability of the myelin basic protein (MBP)-specific T-cell receptor (TCR) repertoire during the course of multiple sclerosis (MS) in three patients who were monitored for three years by gadolinium-enhanced magnetic resonance imaging. Bulk-culture T-cell lines (TCLs) were generated from 3-4 time points for each patient, including times of active and quiescent disease. TCR analysis of these TCLs indicated that both the V alpha and V beta usage was similar over time for each patient. Sequencing of TCRs demonstrated conserved complementarity-determining region 3 (CDR3) sequences within TCLs that expressed the same V alpha segment over time, although the J alpha usage was different for each TCR. This indicates that the population of MBP-reactive T-cells is changing during the course of MS, but that host and/or environmental factors may be selecting T-cells with particular MHC/peptide binding domains.

T cell response to myelin basic protein in the context of the multiple sclerosis-associated HLA-DR15 haplotype: peptide binding, immunodominance and effector functions of T cells

In this study, we evaluated the role of the two functional HLA-DR heterodimers, DR2a (DR alpha paired with the beta chain encoded by DRB5*0101) and DR2b (DR alpha paired with the beta chain encoded by DRB1*1501), that are coexpressed in the multiple sclerosis (MS)-associated haplotype HLA-DR15 Dw2, in presenting myelin basic protein (MBP) peptides to MBP-specific T cell lines (TCL). Our results show that both HLA-DR molecules serve as restriction elements for HLA-DR15-restricted TCL. Slightly higher numbers of TCL use DR2a as restriction element, and the epitopes contained in the immunodominant C-terminal region (131-159) are uniquely restricted by DR2a. The immunodominant middle epitope (81-99) is recognized in the context of both DR2a and DR2b, but this specificity strongly dominates the DR2b-restricted T cell response. Overall, immunodominance in the MBP-specific T cell response correlated well with peptide binding to DR2a or DR2b, demonstrating that the affinity of MHC-peptide interactions is important for shaping the T cell response to this autoantigen. Furthermore, we show that binding of the middle MBP peptide to HLA-DR15 molecules prevents cleavage by cathepsin D, a protease abundantly found in endosomal processing compartments, and thus contributes to its immunodominance. Surprisingly, the restriction element employed by MBP-specific T cell clones influenced the effector function (i.e., cytotoxic activity) of T cells irrespective of their peptide fine specificity.

Immunodominance of a low-affinity major histocompatibility complex-binding myelin basic protein epitope (residues 111-129) in HLA-DR4 (B1*0401) subjects is associated with a restricted T cell receptor repertoire

The pathogenesis of multiple sclerosis (MS) is currently ascribed in part to a T cell-mediated process targeting myelin components. The T cell response to one candidate autoantigen, myelin basic protein (MBP), in the context of HLA-DR15Dw2, has been previously studied in detail. However, the characteristics of cellular immunity in the context of other MS-associated HLA-DR haplotypes are scarcely known. MBP-specific T cell lines (TCL) were generated from HLA-DR4 (B1*0401)-positive MS subjects. Out of 275 MBP-specific TCL, 178 (64. 7%) specifically recognized region MBP(111-129), predominantly in the context of DRB1*0401. The major T cell epitope for MBP recognition corresponded to residues MBP(116-123). These TCL expressed disparate profiles of cytokine secretion and cytotoxicity. T cell receptor analysis, on the other hand, revealed a strikingly limited heterogeneity of rearrangements. In contrast to MBP(81-99), which binds with high affinity to HLA-DR15 and is recognized by a diverse T cell repertoire, MBP(111-129) binds weakly to DRB1*0401, suggesting that only high affinity T cell receptors might be able to efficiently engage such unstable MHC/peptide complexes, thus accounting for the T cell receptor restriction we observed. This study provides new insight about MBP recognition and proposes an alternative mechanism for immunodominance of self-antigen T cell epitopes in humans.

Major histocompatibility complex-controlled protective influences on experimental autoimmune encephalomyelitis are peptide specific

The myelin basic protein (MBP) peptide 63-88-induced experimental autoimmune encephalomyelitis (EAE) and its associated T cell cytokine profile are influenced by the rat major histocompatibility complex (MHC). There is an allele-specific protective influence of the MHC class I region, whereas the MHC class II region display either disease-protective or -promoting effects. To investigate if the MHC-associated protection is dependent on certain combinations of MBP peptide and MHC molecules, we have now used another peptide (MBP 89-101). A broader and different set of rat MHC alleles were associated with EAE induced with MBP 89-101 as compared to MBP 63-88. All EAE-susceptible strains mounted peptide-specific strong T helper (Th) 1-like immune responses in vitro. Immunization of rats with an extended peptide (MBP 87-110) induced EAE associated with the same MHC haplotypes as the 89-101 peptide, except in LEW.1N (RT1 pi) rats which were relatively resistant. Only this strain responded with additional Th2-like and transforming growth factor-beta responses to the peptide in vitro. In vivo depletion of CD8+ cells aggravated the disease in this strain. We conclude that both MHC-controlled promoting and protective influences on EAE are dependent on certain MHC/MBP peptide combinations, and that the 87-110 region of MBP contains a major MHC-associated encephalitogenic epitope in the rat.

Identification of high potency microbial and self ligands for a human autoreactive class II-restricted T cell clone

CD4+ class II-restricted T cells specific for self antigens are thought to be involved in the pathogenesis of most human autoimmune diseases and molecular mimicry between foreign and self ligands has been implicated as a possible mechanism for their activation. In this report we introduce combinatorial peptide libraries as a powerful tool to identify cross-reactive ligands for these T cells. The antigen recognition of a CD4+ T cell clone (TCC) specific for myelin basic protein peptide (MBP) (86-96) was dissected by the response to a set of 220 11-mer peptide sublibraries. Based on the results obtained with the libraries for each position of the antigen, artificial peptides were found that induced proliferative responses at much lower concentrations than MBP(86-96). In addition stimulatory ligands derived from protein sequences of self and microbial proteins were identified, some of them even more potent agonists than MBP(86-96). These results indicate that: (a) for at least some autoreactive CD4+ T cells antigen recognition is highly degenerate; (b) the autoantigen used to establish the TCC represents only a suboptimal ligand for the TCC; (c) a completely random and unbiased approach such as combinatorial peptide libraries can decrypt the spectrum of stimulatory ligands for a T cell receptor (TCR).

The effect of intrathecal MBP synthetic peptides containing epitope P85 VVHFFKNIVTP96 on free anti-MBP levels in acute relapsing multiple sclerosis

Acute relapses of multiple sclerosis (MS) are characterized by elevated Free (F)/Bound (B) anti-MBP ratios during the initial phase, followed by a steady decline of F antibody as the recovery/remission phase develops. The (human) MBP epitope for MS anti-MBP is: Pro85-Val-Val-His-Phe-Phe-Lys-Asn-Ile-Val-Thr-Pro96. In phase one clinical research, synthetic peptides (p) containing this epitope, namely pMBP86-95 and/or pMBP82-98, were intrathecally administered to MS patients with monosymptomatic or polysymptomatic relapses to determine the dosage, frequency and duration of administration which will immediately neutralize F circulating CSF anti-MBP. Patients with monosymptomatic relapses required 50 mg of peptide administered daily for 4-5 days. In patients with polysymptomatic relapses, F anti-MBP can be neutralized with dosages between 50 mg peptide daily for 4 days up to 100 mg twice a day for 2 days; however due to the prolonged nature of polysymptomatic relapses, antibody neutralization could not be maintained by these short courses of intrathecal peptide administration. Intravenous administration of these same peptides did not prevent occurrence of future relapses.

Oligoclonal CD4+CD57+ T-Cell Expansions Contribute to the Imbalanced T-Cell Receptor Repertoire of Rheumatoid Arthritis Patients

A peculiar feature of rheumatoid arthritis patients is that they carry clonally expanded CD4+ and CD8+ cells in the peripheral blood. While the distortion of the repertoire of CD8+ cells has been ascribed to the increase of CD8+CD57+ large granular lymphocytes, often detected in these patients, the mechanism responsible for the clonal expansion of CD4+ cells remains unexplained. Here, we report that CD4+CD57+ cells, that in healthy individuals represent a small subset of peripheral CD4+ lymphocytes, are significantly expanded in the peripheral blood of a considerable percentage of rheumatoid arthritis patients. Furthermore, the expansion of these lymphocytes appears to correlate with the presence of rheumatoid factor. The molecular analysis of the T-cell receptor variable beta segments expressed by the CD4+CD57+ cells enriched in rheumatoid arthritis patients showed that they use restricted repertoires, that partially overlap with those of their CD4−CD57+ counterpart. The structural feature of the receptor ligand expressed by these cells revealed that their expansion is most likely mediated by strong antigenic pressures. However, since we also found that CD4+CD57+ and CD4−CD57+ cells can share the same clonal specificity, it is likely that their selection is not mediated by conventional major histocompatibility complex restricted mechanisms. Thus, while our data demonstrate that CD4+CD57+ cells play an important role in establishing the imbalance of the CD4+ cell repertoire observed in rheumatoid arthritis patients, they also suggest that these cells have common features with mouse CD4+CD8−NK1.1+/T cells.

Missense Mutations in the Fas Gene Resulting in Autoimmune Lymphoproliferative Syndrome: A Molecular and Immunological Analysis

Programmed cell death (or apoptosis) is a physiological process essential to the normal development and homeostatic maintenance of the immune system. The Fas/Apo-1 receptor plays a crucial role in the regulation of apoptosis, as demonstrated by lymphoproliferation in MRL-lpr/lpr mice and by the recently described autoimmune lymphoproliferative syndrome (ALPS) in humans, both of which are due to mutations in the Fas gene. We describe a novel family with ALPS in which three affected siblings carry two distinct missense mutations on both the Fas gene alleles and show lack of Fas-induced apoptosis. The children share common clinical features including splenomegaly and lymphadenopathy, but only one developed severe autoimmune manifestations. In all three siblings, we demonstrated the presence of anergic CD3+CD4−CD8− (double negative, [DN]) T cells; moreover, a chronic lymphocyte activation was found, as demonstrated by the presence of high levels of HLA-DR expression on peripheral CD3+ cells and by the presence of high levels of serum activation markers such as soluble interleukin-2 receptor (sIL-2R) and soluble CD30 (sCD30).

Encephalitogenic potential of myelin basic protein-specific T cells isolated from normal rhesus macaques

Myelin basic protein (MBP)-specific T cells are implicated in the pathogenesis of multiple sclerosis and are targets of selective immunotherapies. However, autoantigen-specific T cells can also be isolated from healthy individuals. Their functional potential is unknown and obviously cannot be tested in humans. We approached this question in a closely related primate species, the rhesus monkey. CD4+ T cell lines specific for MBP were isolated from normal rhesus monkeys using the same primary limiting dilution technique that is now widely used to generate human autoreactive T cell clones in vitro. Three different epitopes were recognized by three rhesus T cell lines isolated from three different monkeys. Upon activation, all lines produced interferon-gamma, interleukin-2, tumor necrosis factor-alpha, and granulocyte/macrophage colony-stimulating factor but neither interleukin-4 nor transforming growth factor-beta. The MBP-specific T cells were injected intravenously without adjuvant into the nonirradiated autologous monkey. One of the three rhesus monkeys developed an encephalomyelitis with a pleocytosis in the spinal fluid and perivascular infiltrates in the leptomeninges, spinal nerve roots and cerebral cortex. The data demonstrate that the normal immune repertoire of a primate species contains MBP-specific CD4+ T cells that are able to induce an autoimmune encephalomyelitis upon transfer into the nonirradiated autologous recipient.

Immunological aspects of experimental allergic encephalomyelitis and multiple sclerosis and their application for new therapeutic strategies

The etiology of multiple sclerosis (MS), a demyelinating disorder of the central nervous system (CNS), is not yet known. Immunological, clinical and pathological studies suggest, however, that T lymphocytes directed against myelin antigens are involved in the pathogenesis of MS. The examination of an experimental animal model for MS, experimental allergic encephalomyelitis (EAE), demonstrated that myelin basic protein-(MBP) or proteolipidprotein-(PLP) specific T cells mediate the destruction of CNS myelin. In recent years, elegant studies in EAE showed that encephalitogenic T cells recognize short peptides of MBP or PLP in the context of MHC/HLA-class II molecules, express a restricted number of T cell receptor (TCR) molecules and secrete interferon-gamma and tumor necrosis factor-alpha/beta. Understanding the pathogenetic steps of demyelination at the molecular level led to highly specific immunotherapies of EAE targeting each individual molecule. MBP- and PLP-specific T cells with similar properties could also be isolated from MS patients and control individuals. Due to their heterogeneity in terms of specificity, function and TCR usage, it was difficult, however, to draw definite conclusions from these results, so far. The recent approval of interferon-beta, a cytokine that antagonizes a number of the effects of interferon-gamma, for the treatment of MS has raised great interest in examining novel strategies for immunotherapies in MS. The basic concepts as well as the current candidates for such new immunotherapies will be outlined in this brief article.

Genetics of multiple sclerosis--how could disease-associated HLA-types contribute to pathogenesis?

Multiple sclerosis is a chronic demyelinating disease of the central nervous system in young adults. It is considered a T cell-mediated autoimmune disease which is probably triggered by exogenous events, e.g. infectious agents, in susceptible individuals. Population, family and twin studies indicate that genetic factors and most likely several genes are associated with disease, but it is clear from the concordance rates of identical twins (25-30%) that genetic background as well as exogenous or somatic events are required to develop disease. Among many candidate genes which have been analyzed during recent years, the strongest association was shown for genes of the HLA-class II complex, in particular HLA-DR15 Dw2 and -DQw6. At present, it is not clear how the expression of a particular HLA-class II gene translates into susceptibility to develop an organ-specific autoimmune disease. Potential explanations how this could occur will be discussed.

Complementary mutations in an antigenic peptide allow for crossreactivity of autoreactive T-cell clones

T cells recognize antigen by formation of a trimolecular complex in which the T-cell receptor (TCR) recognizes a specific peptide antigen within the groove of a major histocompatibility complex (MHC) molecule. It has generally been assumed that T-cell recognition of two distinct MHC-antigen complexes is due to similarities in the three-dimensional structure of the complexes. Here we report results of experiments examining the crossreactivity of TCRs recognizing the myelin basic protein peptide MBPp85-99 and several of its analogs in the context of MHC. We demonstrate that single conservative amino acid substitutions of the antigenic peptide at the predominant TCR contact residues at positions 91 and 93 totally abrogate reactivity of specific T-cell clones. Yet, when a conservative substitution is made at position 91 concomitant with a substitution at position 93, the T-cell clones regain reactivity equivalent with that of the original stimulating peptide. Thus, the exact nature of the amino acid side chains engaging one TCR functional pocket may change the apparent selectivity of the other predominant TCR functional pocket, thus suggesting a remarkable degree of receptor plasticity. This ability of the TCR-MHC-peptide complex to undergo conformational changes provides a conceptual framework for reconciling the apparent paradox of the extreme selectivity of the TCR and its remarkable crossreactivity with different MHC-peptide complexes.

Differential activation of human autoreactive T cell clones by altered peptide ligands derived from myelin basic protein peptide (87-99)

We have examined the functional consequences induced by interaction of DR2a-restricted myelin basic protein (MBP) (87-99)-specific T cell clones (TCC) with altered peptide ligands (APL) derived from MBP peptide (87-99). The immunodominant MBP peptide (87-99) has been implicated as a candidate antigen in multiple sclerosis (MS) by several lines of evidence. In the present study, we have defined the T cell receptor (TCR) contact residues for DR2a-restricted, (87-99)-specific T helper type 1 T cells to design APL suitable to modify the functions of such T cells potentially relevant for the pathogenesis of MS. We show that neutral (L-alanine substitutions) or conservative exchanges of the primary and secondary TCR contact residues lead to various alterations of T cell function, ranging from differences in interleukin-2 receptor up-regulation to anergy induction and TCR antagonism. The potential usefulness of APL as an immunomodulating therapy for DR2+ MS patients is discussed.

Expansion of a recurrent V beta 5.3+ T-cell population in newly diagnosed and untreated HLA-DR2 multiple sclerosis patients

We have used a PCR-based technology to study the V beta 5 and V beta 17 repertoire of T-cell populations in HLA-DR2 multiple sclerosis (MS) patients. We have found that the five MS DR2 patients studied present, at the moment of diagnosis and prior to any treatment, a marked expansion of a CD4+ T-cell population bearing V beta 5-J beta 1.4 beta chains. The sequences of the complementarity-determining region 3 of the expanded T cells are highly homologous. One shares structural features with that of the T cells infiltrating the central nervous system and of myelin basic protein-reactive T cells found in HLA-DR2 MS patients. An homologous sequence was not detectable in MS patients expressing DR alleles other than DR2. However, it is detectable but not expanded in healthy DR2 individuals. The possible mechanisms leading to its in vivo proliferation at the onset of MS are discussed.

Binding of ALA-substituted analogs of HA306-320 to DR1101, DR1301, and DR0402 molecules: correlation of DR-peptide interactions with recognition by a single TCR

We tested the hypothesis that a cross-reactive T-cell clone could recognize HA306-320 peptide complexed to autologous HLA-DR1101, and also to allogenic HLA-DR0402 and HLA-DR1301 molecules, because of similar orientations of HA306-320 side chains in the groove of the three DR molecules. To approach peptide orientations in each HLA groove we compared the capacity of Ala-monosubstituted analogs to bind and be presented by DR1101, DR0402, and DR1301. Results indicated that the orientation of HA306-320 in DR1101 was grossly similar to the known orientation of HA307-319 in DR0101. Data suggested many similarities in peptide orientations in DR0402 and DR1301 as well. However, differences in binding were also observed. Ala substitution of Y309 had much less effect on peptide binding to DR1301 and DR0402 than to DR1101 and Ala-substitution of T314 increased affinity for DR1301 but not for DR1101 and DR0402. These alterations of peptide-DR interactions were probably communicated to the upper peptide surface. Indeed, the levels of T-cell clone reactivities against analogs mutated at positions predicted to face the TCR were lower when complexed to allogeneic DR molecules than when complexed to DR1101. Yet these epitopic alterations are likely subtle, since the decreased reactivity of the clone to allogeneic molecules could be compensated by peptide substitution at Y309, predicted to face the MHC.

The pattern of production of cytokine mRNAs is markedly altered at the onset of multiple sclerosis

Using two independent PCR-based quantification techniques, we have determined the levels of IL1 beta, IL2, IL4, IL6, IL10, IFN gamma and TNF alpha mRNA in multiple sclerosis patients at the moment of diagnosis of the disease and prior to any immunosuppressive treatment. These patients exhibit markedly reduced IL2 and IL10 mRNA expression accompanied by decreased levels of TNF alpha mRNA. Our results add to the evidence that IL10 plays a role in multiple sclerosis and suggest that decreased production of this interleukin allows the proliferation of autoreactive T cells at the onset of the disease.

T cell receptor peptides in treatment of autoimmune disease: rationale and potential

The natural tendency in T cell-mediated autoimmune conditions to develop focused antigen-specific responses that over-utilize certain T cell receptor (TCR) V region segments prompts the induction of anti-TCR-specific T cells and antibodies that can inhibit the pathogenic T cells and promote recovery from disease. This natural regulatory network can be manipulated by injecting synthetic peptide vaccines that correspond to segments of the over-expressed V genes. In experimental autoimmune encephalomyelitis (EAE), an animal model for the human disease multiple sclerosis (MS), the pathogenic T cells are directed at myelin components, including basic protein (MBP). In some strains such as the Lewis rat and the PL/J mouse, the encephalitogenic BP-specific T cells overexpress a particular V region gene (V beta 8.2) in the TCR. In vivo administration of V beta 8.2 peptides in rats or mice can prevent and treat EAE by boosting regulatory anti-V beta 8.2-specific T cells that inhibit but do not delete the encephalitogenic specificities. This regulation is mediated by soluble factors, suggesting that the presence of regulatory TCR-specific T cells within the target organ (the central nervous system) may inhibit not only the stimulating V beta 8.2 + T cells, but also bystander T cells bearing different V genes. Parallel studies in MS patients have revealed striking V gene biases among BP-specific T cell clones from some patients that provided a rationale for TCR peptide therapy. Injection of V beta 5.2 and V beta 6.1 peptides boosted the frequency of TCR peptide-specific T cells and reduced responses to BP, in some cases with clinical benefit, indicating the presence of an anti-TCR regulatory network in humans that may also be manipulated with TCR peptide therapy.

Human self-reactive T cell clones expressing identical T cell receptor beta chains differ in their ability to recognize a cryptic self-epitope

Recognition of self-antigens by T lymphocytes is a central event in autoimmunity. Understanding of the molecular interactions between T cell receptors (TCR) and self-epitopes may explain how T cells escape thymic education and initiate an autoimmune reaction. We have studied five human in vivo activated T cell clones specific for the region 535-551 of human thyroid peroxidase (TPO) established from a Graves' patient. Three clones (37, 72, and 73) expressed identical TCR beta and alpha chains rearranging V beta 1.1 and V alpha 15.1, and were considered sister clones. Clone 43 differed from clone 37 and its sisters in the J alpha region only. Clone NP-7 expressed V beta 6.5 but rearranged two in-frame TCR alpha chain, both using the V alpha 22.1 segment. Fine epitope mapping using nested peptides showed that clones using identical TCR beta chains, identical V alpha, but a different J alpha recognized distinct, nonoverlapping epitopes in the TPO 535-551 region. This finding shows that a different J alpha region alone leads to a heterogeneous pattern of recognition. This indicates that the "restricted" TCR V region usage sometimes found in autoimmune diseases may not always correspond to identical epitope recognition. To confirm that clones 37 (and its sisters) and 43 recognize different epitopes, the T cell clones were stimulated with a TPO-transfected autologous Epstein-Barr virus (EBV) cell line (TPO-EBV) that presents TPO epitopes afer endogenous processing. Only clone 37 and its sisters recognizes the TPO-EBV cell line, suggesting that the epitope recognized by clone 43 is not presented upon endogenous processing. We have shown that thyroid epithelial cells (TEC), the only cells that produce TPO, express HLA class II molecules in Graves' disease and can act as an antigen-presenting cells, presenting TPO after endogenous processing to autoantigen-reactive T cell clones. We tested, therefore, whether autologous TEC induced the same pattern of stimulation as TPO-EBV; T cell clone 37 recognizes the TEC, whereas it is stimulated poorly by the TPO loaded to autologous peripheral blood mononuclear cells (PBMC). Clone 43, which fails to recognize the TPO-EBV, also fails to recognize the TEC, but is activated by exogenous TPO presented by autologous PBMC. These results show that exogenous versus endogenous processing in vivo generates a different TPO epitope repertoire, producing a "cryptic" epitope (epitope not always available for recognition). Our findings define a route by which human self-reactive T cells may escape thymic selection and become activated in vivo, thus possibly leading to autoimmunity.

Treatment of experimental encephalomyelitis with a peptide analogue of myelin basic protein

Following induction of experimental encephalomyelitis with a T-cell clone, L10C1, that is specific for the myelin basic protein epitope p87-99, the inflammatory infiltrate in the central nervous system contains a diverse collection of T cells with heterogeneous receptors. We show here that when clone L10C1 is tolerized in vivo with an analogue of p87-99, established paralysis is reversed, inflammatory infiltrates regress, and the heterogeneous T-cell infiltrate disappears from the brain, with only the T-cell clones that incited disease remaining in the original lesions. We found that antibody raised against interleukin-4 reversed the tolerance induced by the altered peptide ligand. Treatment with this altered peptide ligand selectively silences pathogenic T cells and actively signals for the efflux of other T cells recruited to the site of disease as a result of the production of interleukin-4 and the reduction of tumour-necrosis factor-alpha in the lesion.

TCR beta PCR from crude preparations for restriction digest or sequencing

T cell specificity is determined by the combinatorial association of specific variable (V), diversity (D), and junctional (J) regions. Clones of T cells (clonality) can occur, in the blood or in tissue, after proliferation of activated T cells. Determining clonality in mutation assays is necessary to distinguish between mutants and mutational events. We have developed a novel approach to determine clonality among T cell isolates, using restriction digests of PCR-amplified cDNA of the T cell receptor beta gene. The T cell receptor beta gene was PCR-amplified by use of a consensus primer, beginning from a cell pellet of 2,000-5,000 cells or from extracted RNA. This TCR (T cell receptor) beta chain PCR product can also be directly sequenced, allowing simple and easy identification of Vbeta and CDR3 sequence from a small number of cells. The utility of this method is demonstrated by PCR, restriction digest, and sequencing of the TCR beta cDNA from eight T cell clones isolated from 2 individuals. A clone of three identical isolates (one 3-mer) and a clone of two identical isolates (one 2-mer) were determined from restriction digests using two different enzymes. This new method is an easier and more rapid way of determining clonality than traditional methods, e.g., Southern blotting.

Multiple sclerosis

Multiple sclerosis is a chronic disease that begins in late adolescence or adulthood. It is highly variable in its expression and severity. It is believed to be autoimmune in nature. The cause is unknown; both genetic and environmental factors have been implicated in the pathogenesis. MS generally presents with the acute or subacute onset of neurologic abnormalities that may wax and wane over many years. Diagnosis is generally made by means of observation of the clinical course in conjunction with a neurologic examination and laboratory tests. These tests may include magnetic resonance imaging of the head and spine, lumbar puncture, and evoked potentials. Treatment is based on general supportive care, the use of corticosteroids for relapses, and symptomatic management of ongoing problems. The frequency of relapses can be reduced with interferon-beta (Betaseron). Copolymer 1 and interferon-beta la are being evaluated by the U.S. Food and Drug Administration for approval for use for reduction in the frequency of relapses in relapsing-remitting MS. Treatment of chronic progression is often attempted with immunosuppressive agents such as corticosteroids, azathioprine, and cyclophosphamide. Use of other agents is being investigated.

Clonal dominance and selection for similar complementarity determining region 3 motifs among T lymphocytes responding to the HLA-DR3-associated Mycobacterium leprae heat shock protein 65-kd peptide 3-13

In order to establish whether specific MHC class II-peptide complexes are capable of selecting TCR V regions, we investigated in detail the TCR beta chain used in the recognition of HLA-DR3 restricted hsp65 peptide 3-13 in a tuberculoid leprosy patient. Using RT-PCR, a clear dominance of the TCRBV5 gene family was observed in a hsp65 peptide 3-13-specific T-cell line; however, not in fresh, unstimulated PBMCs, PHA-stimulated PBMCs, or a T-cell line specific for tetanus toxoid. DNA sequence analysis of the TCR V regions, comprising TCRBV5 genes, derived from the hsp65 peptide 3-13-specific T-cell line revealed the exclusive usage of the TCRBV55S1 gene segment and a predominance of one V-D-J gene rearrangement, which is indicative of clonal expansion of these T lymphocytes. Additional highly similar V-D-J gene rearrangements were detected at a low level in this hsp65 peptide 3-13 specific T-cell line. These conserved junctional regions (CDR3 regions) could not be detected within the TCRBV5 gene family of fresh PBMCs, PHA-stimulated PBMCs, hsp65, and tetanus-toxoid-specific T-cell lines from this patient. The observations in this tuberculoid leprosy patient reveal that an HLA class-II-restricted T-cell response results in selection of TCRBV regions which are highly similar in amino acid composition to the CDR3 region within the expanding TCRBV regions.

Fine specificity of the antibody response to myelin basic protein in the central nervous system in multiple sclerosis: the minimal B-cell epitope and a model of its features

T cells, B cells, and antibody are found in the white matter of the central nervous system in multiple sclerosis. The epitope center for the antibody response to human myelin basic protein (MBP) fits precisely the minimal epitope Pro85-Val-Val-His-Phe-Phe-Lys-Asn-Ile-Val-Thr-Pro96 for that reported for HLA DR2b (DRB1*1501)-restricted T cells that recognize MBP [Wucherpfenning, K.W., Sette, A., Southwood, S., Oseroff, C., Matsui, M., Strominger, J. & Hafler, D. (1994) J. Exp. Med. 179, 279-290], and overlaps with the reported DR2a-restricted epitope for T cells reactive to MBP [Martin, R., Howell, M. D., Jaraquemada, D., Furlage, M., Richert, J., Brostoff, S., Long, E. O., McFarlin, D. E. & McFarland, H. F. (1991) J. Exp. Med. 173, 19-24]. We describe a molecular model of this epitope.

Experimental autoimmune encephalomyelitis in rodents as a model for human demyelinating disease

The cause of multiple sclerosis (MS) is unknown, but the pathology is consistent with an immunological etiology. Studies conducted with the animal model of MS, experimental autoimmune encephalomyelitis (EAE), have provided insight into how the immune system can provoke an immunopathological response characteristic of that seen in MS. The use of inbred rats and mice for studies of EAE has been especially rewarding with respect to the identification of the epitopes of encephalitogenic antigens responsible for the induction of this autoimmune disease and in elucidating the effector mechanism underlying EAE. Moreover, it has also been possible to ascertain how EAE can be regulated, leading to therapeutic modalities which have been applied in clinical studies of MS patients. This review briefly summarizes studies of EAE in rodents, drawing comparisons with immunological findings reported in patients with MS. It is clear that important lessons can be learned from the detailed investigation of animal models that may be applicable to human immunological disorders.

Unique T-cell receptor junctional sequences found in multiple sclerosis and T-cells mediating experimental allergic encephalomyelitis

We have used two approaches to isolate TCR sequences that are unique to patients with multiple sclerosis. One strategy was to sequence TCR gene rearrangements directly from MS lesions. The second strategy utilized T-cell clones with a selectable mutation that are found only in MS patients. The selection of T-cell clones with mutations in the hypoxanthine guanine phosphoribosyltransferase (hprt) gene was used to isolate T-cells reactive to myelin basic protein (MBP) in patients with multiple sclerosis (MS). These T-cell clones are activated in vivo, and are not found in healthy individuals. The third complementarity determining regions (CDR3) of the T-cell receptor (TCR) alpha and beta chains are the putative contact sites for peptide fragments of MBP bound in the groove of the HLA molecule. The TCR V gene usage and CDR3s of these MBP-reactive hprt- T-cell clones are homologous to TCRs from other T-cells relevant to MS, including T-cells causing experimental allergic encephalomyelitis (EAE) and T-cells found in brain lesions and in the cerebrospinal fluid (CSF) of MS patients. In vivo activated MBP-reactive T-cells in MS patients may be critical in the pathogenesis of MS.

A review of T-cell receptors in multiple sclerosis: clonal expansion and persistence of human T-cells specific for an immunodominant myelin basic protein peptide

Understanding the immune response to myelin antigens in regard to the peptide/MHC/TCR complex is important in defining pathogenesis of demyelinating autoimmune diseases and in developing antigen-specific therapies. We previously reported that individual multiple sclerosis patients may use certain dominant TCR V beta chains to recognize immunodominant MBP peptides. In examining the TCR beta chain usage, we observed repeated TCR VDJ sequences among different T-cell lines isolated from the same patient. This suggested that a few expanded T-cell clones may dominate the immune response to immunodominant MBP peptides. Here, we report experiments where TCR rearrangements were used as a probe for the clonal origin of MBP specific T-cells cultured from blood lymphocytes of MS patients and normal subjects. In two patients with the DR2 haplotype that were analyzed in detail, the T-cell response to MBP was focused on the MBP (84-102) peptide and in vivo expanded population(s) dominated the response to the MBP (84-102) peptide. Two MBP (84-102) specific T-cell clones from a normal subject with the DR2 haplotype were also found to have identical TCR sequences. Clonality was proven by demonstrating that independent clones had identical TCR alpha and beta chain sequences as well as identical sequences of a TCR gamma chain or of a second TCR alpha chain rearrangement. These data suggest that the response to human MBP is dominated in at least some subjects by expanded clones that may persist in vivo for relatively long periods of time.

Healthy human T-cell receptor beta-chain repertoire. Quantitative analysis and evidence for J beta-related effects on CDR3 structure and diversity

Analysis of TCR repertoire usage and clonality is of potential value in understanding the pathogenesis of a number of human immune-mediated diseases. In diseases that are likely to be dependent on antigen-driven T cells, it has been suggested that particular TCR junctional region or CDR3 sequences may be critical. Rigorous methods for TCR analysis which are both quantitative and qualitative are therefore required. Of those commonly available, only anchor and inverse PCR are capable of giving high-quality information on V, D, N, and J region usage, but it has not been established whether both methods are quantitatively or analytically equivalent. We show here that both methods detected considerable variability in the usage of V beta and J beta segments in the peripheral blood repertoire of a normal individual. No preferential V-J pairing could be demonstrated. An excess usage of J beta 2 family members was indicated by both methods, although the relative usage of different J beta 2 families differed between the two techniques. The predominantly used V beta usage showed that for some families, estimates of their frequency in the repertoire differed significantly between the anchor and inverse libraries. When sampling relatively few clones the variation between V beta families estimated using the two methods can be considerable. This is likely to be a result of sampling error from a large gene family. Large-scale screening of several thousand clones is recommended to confirm the absolute values obtained from sequencing. Variation in CDR3 length appeared to be normally distributed, suggesting that a statistically optimal junctional region length may have been selected for contact with antigen. CDR3 length distribution differs significantly between receptors, which have rearranged to J beta 1 versus J beta 2 families, with the J beta 2-associated CDR3 on average between 0.5 and 1.2 of an amino acid longer. Thus the TCR beta junctional region repertoire of humans is subject to structural constraints associated with J beta usage. It will be important to establish whether variation in CDR3 length and J beta usage exists between subsets of human T cells in order to interpret TCR repertoire data from disease and control tissues.

Bacterial pyrogenic exotoxins as superantigens

The recent discovery of the mode of interaction between a group of microbial proteins known as superantigens and the immune system has opened a wide area of investigation into the possible role of these molecules in human diseases. Superantigens produced by certain viruses and bacteria, including Mycoplasma species, are either secreted or membrane-bound proteins. A unique feature of these proteins is that they can interact simultaneously with distinct receptors on different types of cells, resulting in enhanced cell-cell interaction and triggering a series of biochemical reactions that can lead to excessive cell proliferation and the release of inflammatory cytokines. However, although superantigens share many features, they can have very different biological effects that are potentiated by host genetic and environmental factors. This review focuses on a group of secreted pyrogenic toxins that belong to the superantigen family and highlights some of their structural-functional features and their roles in diseases such as toxic shock and autoimmunity. Deciphering the biological activities of the various superantigens and understanding their role in the pathogenesis of microbial infections and their sequelae will enable us to devise means by which we can intervene with their activity and/or manipulate them to our advantage.

Multiple sclerosis: immune mechanism and update on current therapies

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system (CNS) afflicting approximately 250,000 individuals in the United States. This inflammatory disease has variable clinical manifestations, ranging from a relapsing-remitting course to a chronic progressive disease. Approximately one third of MS patients have chronic progressive disease often leading to severe impairment of mobility, paralysis, poor vision, and disturbances of bladder and bowel function. Although the etiology and pathogenesis remain unknown, accumulating evidence supports the hypothesis that exposure to an as-yet-unidentified infectious agent(s) triggers an aberrant immune response against self nervous tissue in genetically susceptible individuals. The tenfold higher concordance rate for MS in monozygotic twins compared to dizygotic twins, the increased incidence of MS in women compared to men (2:1), and the familial and racial occurrence of MS provide strong evidence that genetic factors influence susceptibility to MS. The major predisposing genes in MS are the human leukocyte antigen (HLA) class II molecules, DR15 and DQw6, molecularly defined as HLA-DRB1, 1501-DQA1 0102-DQB1 0602. In certain ethnic groups, MS susceptibility is more strongly associated with other DR molecules. Environmental factors are also believed to play a role, as suggested by the unique worldwide prevalence, migration effects, and epidemiological studies. Increased serum and cerebrospinal fluid antibody titers to numerous viruses have been reported; however, there have been no confirmed studies detecting viral RNA or antigen in MS brain tissue. At the present time, no known treatment can significantly alter the progression of MS. Based on the postulate that MS is an autoimmune disease associated with abnormalities in immunoregulation, a number of different immunosuppressive and immunomodulating agents have been tested as therapeutic modalities. In this article, we review the circumstantial evidence suggesting that immune system abnormalities are associated with the disease process, and provide an update on current therapies used in MS.

HLA DRB4 0101-restricted immunodominant T cell autoepitope of pyruvate dehydrogenase complex in primary biliary cirrhosis: evidence of molecular mimicry in human autoimmune diseases

We established six T cell clones specific for pyruvate dehydrogenase complex (PDC)-E2 peptides from four different patients with primary biliary cirrhosis using 33 different peptides of 17-20 amino acid residues corresponding to human PDC-E2 as stimulating antigens. The minimal T cell epitopes of these six T cell clones were all mapped to the same region of the PDC-E2 peptide 163-176 (GDLLAEIETDKATI), which corresponds to the inner lipoyl domain of PDC-E2. The HLA restriction molecules for this epitope were all identified as HLA DRB4 0101. The common essential amino acids of this epitope for these T cell clones were E, D, and K at positions 170, 172, and 173, respectively; other crucial amino acids for this epitope differed in each T cell clone. In addition, the alanine-substituted peptides at positions 170 and 173, but not 172, inhibited the proliferation of all T cell clones induced by the original peptide of human PDC-E2 163-176, indicating that amino acid D at position 172 is a critical MHC-binding site for all T cell clones tested. Interestingly, all T cell clones reacted to PDC-E2 peptide 36-49 (GDLIAEVETDKATV), which corresponds to the outer lipoyl domain of human PDC-E2. Furthermore, one T cell clone cross-reacted with exogenous antigens such as Escherichia coli PDC-E2 peptide 31-44/134-147/235-248 (EQSLITVEGDKASM), which has an EXDK sequence. This is a definite demonstration of the presence of molecular mimicry at the T cell clonal level in human autoimmune diseases. It is also considered possible to design peptide-specific immunotherapy based on the findings of T cell autoepitopes in primary biliary cirrhosis.

Identification of the epitope recognized by the human V beta 5-specific monoclonal antibody 42/1C1. Potential implications for disease therapy

A panel of T-cell clones was generated that was specific for amino acid residues 4-13 of the mycobacterial 65-kd stress protein. All the clones were found to express a member of the V beta 5 family, as defined by PCR. However, the clones could be differentiated on the basis of different staining characteristics with the mAb 42/1C1. This antibody is known to recognize both V beta 5.2 and V beta 5.3, as was the PCR primer pair used in the analysis. Sequencing of the TCRs revealed that those clones which were not stained by 42/1C1 expressed a previously unidentified member of the V beta 5 family. By comparing the sequences of the V beta 5 family members that are recognized by 42/1C1 with those that are not, we were able to identify a probable epitope for the antibody. It is also clear from our data that the TCRs of T cells recognizing identical MHC-peptide combinations, although very similar, may be differentiated by mAbs, thereby posing potential problems in any proposed disease therapy involving treatment with monoclonals.

Structure and specificity of T cell receptors expressed by potentially pathogenic anti-DNA autoantibody-inducing T cells in human lupus

The production of potentially pathogenic anti-DNA autoantibodies in SLE is driven by special, autoimmune T helper (Th) cells. Herein, we sequenced the T cell receptor (TCR) alpha and beta chain genes expressed by 42 autoimmune Th lines from lupus patients that were mostly CD4+ and represented the strongest inducers of such autoantibodies. These autoimmune TCRs displayed a recurrent motif of highly charged residues in their CDR3 loops that were contributed by N-nucleotide additions and also positioned there by the recombination process. Furthermore, Th lines from four of the five patients showed a marked increase in the usage of the V alpha 8 gene family. Several independent Th lines expressed identical TCR alpha and/or beta chain sequences indicating again antigenic selection. 10 of these Th lines could be tested further for antigenic specificity. 4 of the 10 pathogenic anti-DNA autoantibody-inducing Th lines responded to the non-histone chromosomal protein HMG and two responded to nucleosomal histone proteins; all presented by HLA-DR molecules. Another Th line responded to purified DNA more than nucleosomes. Thus, these autoimmune Th cells of lupus patients respond to charged epitopes in various DNA-binding nucleoproteins that are probably processed and presented by the anti-DNA B cells they selectively help.