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

TScan-II: A genome-scale platform for the de novo identification of CD4+ T cell epitopes

CD4+ T cells play fundamental roles in orchestrating immune responses and tissue homeostasis. However, our inability to associate peptide human leukocyte antigen class-II (HLA-II) complexes with their cognate T cell receptors (TCRs) in an unbiased manner has hampered our understanding of CD4+ T cell function and role in pathologies. Here, we introduce TScan-II, a highly sensitive genome-scale CD4+ antigen discovery platform. This platform seamlessly integrates the endogenous HLA-II antigen-processing machinery in synthetic antigen-presenting cells and TCR signaling in T cells, enabling the simultaneous screening of multiple HLAs and TCRs. Leveraging genome-scale human, virome, and epitope mutagenesis libraries, TScan-II facilitates de novo antigen discovery and deep exploration of TCR specificity. We demonstrate TScan-II's potential for basic and translational research by identifying a non-canonical antigen for a cancer-reactive CD4+ T cell clone. Additionally, we identified two antigens for clonally expanded CD4+ T cells in Sjögren's disease, which bind distinct HLAs and are expressed in HLA-II-positive ductal cells within affected salivary glands.

T Cell Receptor Sequences Amplified during Severe COVID-19 and Multisystem Inflammatory Syndrome in Children Mimic SARS-CoV-2, Its Bacterial Co-Infections and Host Autoantigens

Published hypervariable region V-beta T cell receptor (TCR) sequences were collected from people with severe COVID-19 characterized by having various autoimmune complications, including blood coagulopathies and cardiac autoimmunity, as well as from patients diagnosed with the Kawasaki disease (KD)-like multisystem inflammatory syndrome in children (MIS-C). These were compared with comparable published v-beta TCR sequences from people diagnosed with KD and from healthy individuals. Since TCR V-beta sequences are supposed to be complementary to antigens that induce clonal expansion, it was surprising that only a quarter of the TCR sequences derived from severe COVID-19 and MIS-C patients mimicked SARS-CoV-2 proteins. Thirty percent of the KD-derived TCR mimicked coronaviruses other than SARS-CoV-2. In contrast, only three percent of the TCR sequences from healthy individuals and those diagnosed with autoimmune myocarditis displayed similarities to any coronavirus. In each disease, significant increases were found in the amount of TCRs from healthy individuals mimicking specific bacterial co-infections (especially Enterococcus faecium, Staphylococcal and Streptococcal antigens) and host autoantigens targeted by autoimmune diseases (especially myosin, collagen, phospholipid-associated proteins, and blood coagulation proteins). Theoretical explanations for these surprising observations and implications to unravel the causes of autoimmune diseases are explored.

Vitamin D Actions on CD4(+) T Cells in Autoimmune Disease

This review summarizes and integrates research on vitamin D and CD4⁺ T-lymphocyte biology to develop new mechanistic insights into the molecular etiology of autoimmune disease. A deep understanding of molecular mechanisms relevant to gene–environment interactions is needed to deliver etiology-based autoimmune disease prevention and treatment strategies. Evidence linking sunlight, vitamin D, and the risk of multiple sclerosis and type 1 diabetes is summarized to develop the thesis that vitamin D is the environmental factor that most strongly influences autoimmune disease development. Evidence for CD4⁺ T-cell involvement in autoimmune disease pathogenesis and for paracrine calcitriol signaling to CD4⁺ T lymphocytes is summarized to support the thesis that calcitriol is sunlight’s main protective signal transducer in autoimmune disease risk. Animal modeling and human mechanistic data are summarized to support the view that vitamin D probably influences thymic negative selection, effector Th1 and Th17 pathogenesis and responsiveness to extrinsic cell death signals, FoxP3⁺CD4⁺ T-regulatory cell and CD4⁺ T-regulatory cell type 1 (Tr1) cell functions, and a Th1–Tr1 switch. The proposed Th1–Tr1 switch appears to bridge two stable, self-reinforcing immune states, pro- and anti-inflammatory, each with a characteristic gene regulatory network. The bi-stable switch would enable T cells to integrate signals from pathogens, hormones, cell–cell interactions, and soluble mediators and respond in a biologically appropriate manner. Finally, unanswered questions and potentially informative future research directions are highlighted to speed delivery of etiology-based strategies to reduce autoimmune disease.

Defining a new biomarker for the autoimmune component of Multiple Sclerosis: Th40 cells

Multiple Sclerosis (MS) is a chronic inflammatory, neurodegenerative disease. Diagnosis is very difficult requiring defined symptoms and multiple CNS imaging. A complicating issue is that almost all symptoms are not disease specific for MS. Autoimmunity is evident, yet the only immune-related diagnostic tool is cerebral-spinal fluid examination for oligoclonal bands. This study addresses the impact of Th40 cells, a pathogenic effector subset of helper T cells, in MS. MS patients including relapsing/remitting MS, secondary progressive MS and primary progressive MS were examined for Th40 cell levels in peripheral blood and, similar to our findings in autoimmune type 1 diabetes, the levels were significantly (p<0.0001) elevated compared to controls including healthy non-autoimmune subjects and another non-autoimmune chronic disease. Classically identified Tregs were at levels equivalent to non-autoimmune controls but the Th40/Treg ratio still predicted autoimmunity. The cohort displayed a wide range of HLA haplotypes including the GWAS identified predictive HLA-DRB1*1501 (DR2). However half the subjects did not carry DR2 and regardless of HLA haplotype, Th40 cells were expanded during disease. In RRMS Th40 cells demonstrated a limited TCR clonality. Mechanistically, Th40 cells demonstrated a wide array of response to CNS associated self-antigens that was dependent upon HLA haplotype. Th40 cells were predominantly memory phenotype producing IL-17 and IFNγ with a significant portion producing both inflammatory cytokines simultaneously suggesting an intermediary between Th1 and Th17 phenotypes.

Hematopoietic stem cell transplantation in multiple sclerosis

It is widely accepted that the main common pathogenetic pathway in multiple sclerosis (MS) involves an immune-mediated cascade initiated in the peripheral immune system and targeting CNS myelin. Logically, therefore, therapeutic approaches to the disease include modalities aiming at downregulation of the various immune elements that are involved in this immunological cascade. Since the introduction of interferons in 1993, more specific immunoactive drugs have been introduced, but still most of them can, at best, effectively modulate only the early relapsing phases of MS. The more progressed phases of the disease are not efficiently amendable by the existing immunomodulatory drugs. Moreover, localized and compartmentized inflammation in the CNS, which seems to be mostly responsible for the chronic axonal damage and resulting progression of disability, is less affected by the current drugs. A more radical approach to suppress all the inflammation in MS, including that into the CNS, could theoretically be achieved with high-dose immunosuppression using strong cytotoxic medications and resetting of the immune system by hematopoietic stem cell transplantation (HSCT). HSCT, both allogeneic and autologous, has been tried as a novel therapeutic approach in various autoimmune diseases. During the last 15 years several (mostly open) clinical studies evaluated the effect of HSTC on MS patients; the published papers showed that a high proportion of the HSCT-treated MS patients were stabilized, or even improved after the transplantation and have generally indicated a beneficial effect on disease progression. In this review, the rationale of HSCT and the summary of the results of the existing clinical trials are presented. Despite the fact that it is difficult to collectively summarize the results of all the trials, due to lack of uniformity in the conditioning and treatment protocols and of completed controlled studies, these clinical studies have provided a strong 'proof of concept' for HSCT in MS and have significantly contributed to our understanding of the advantages and disadvantages of each approach and HSCT protocol.

Immunotherapy of multiple sclerosis: the state of the art

It is widely accepted that the main common pathogenetic pathway in multiple sclerosis (MS) involves an immune-mediated cascade initiated in the peripheral immune system and targeting CNS myelin. Logically, therefore, the therapeutic approaches to the disease include modalities aiming at downregulation of the various immune elements that are involved in this immunologic cascade. Since the introduction of interferons in 1993, which were the first registered treatments for MS, huge steps have been made in the field of MS immunotherapy. More efficious and specific immunoactive drugs have been introduced and it appears that the increased specificity for MS of these new treatments is paralleled by greater efficacy. Unfortunately, this seemingly increased efficacy has been accompanied by more safety issues. The immunotherapeutic modalities can be divided into two main groups: those affecting the acute stages (relapses) of the disease and the long-term treatments that are aimed at preventing the appearance of relapses and the progression in disability. Immunomodulating treatments may also be classified according to the level of the 'immune axis' where they exert their main effect. Since, in MS, a neurodegenerative process runs in parallel and as a consequence of inflammation, early immune intervention is warranted to prevent progression of relapses of MS and the accumulation of disability. The use of neuroimaging (MRI) techniques that allow the detection of silent inflammatory activity of MS and neurodegeneration has provided an important tool for the substantiation of the clinical efficacy of treatments and the early diagnosis of MS. This review summarizes in detail the existing information on all the available immunotherapies for MS, old and new, classifies them according to their immunologic mechanisms of action and proposes a structured algorithm/therapeutic scheme for the management of the disease.

T cell receptor variable β20-1 harbors a nucleotide binding pocket in the CDR2β loop

Novel aspects of T cells containing TCRVβ20-1 are numerous, ranging from pathogen specific reactivity to specific tissue homing, or possible T cell subsets. Recently, it was demonstrated that TCR itself could become reactive by binding to small molecules free of the pHLA interface. Our work here was to identify a natural ligand binding to an identified pocket on the CDR2β loop of these TCR. Using docking of suspected ligands, we were able to show Guanine and Adenine di- and tri-nucleotides readily bind to the identified site. Comparing these with small molecule sites found on other TCR types, we show this interaction is novel. With further molecular dynamic simulations, these sites are shown to be plausible by conducting simple computational based solubility tests as cross validation. Combined with simple proliferative responses, the identified nucleotides are also shown to have functional consequences by inducing T cell proliferation for CD4/Vβ20-1 + T cells, while failing to induce proliferation in other T cell isolates. Merging computational and simple cell assays, this work establishes a role of nucleotides in T cells found to contain this TCR sub-type.

Loss of T cell CD98 H chain specifically ablates T cell clonal expansion and protects from autoimmunity

CD98 H chain (4F2 Ag, Slc3a2) was discovered as a lymphocyte-activation Ag. Deletion of CD98 H chain in B cells leads to complete failure of B cell proliferation, plasma cell formation, and Ab secretion. In this study, we examined the role of T cell CD98 in cell-mediated immunity and autoimmune disease pathogenesis by specifically deleting it in murine T cells. Deletion of T cell CD98 prevented experimental autoimmune diabetes associated with dramatically reduced T cell clonal expansion. Nevertheless, initial T cell homing to pancreatic islets was unimpaired. In sharp contrast to B cells, CD98-null T cells showed only modestly impaired Ag-driven proliferation and nearly normal homeostatic proliferation. Furthermore, these cells were activated by Ag, leading to cytokine production (CD4) and efficient cytolytic killing of targets (CD8). The integrin-binding domain of CD98 was necessary and sufficient for full clonal expansion, pointing to a role for adhesive signaling in T cell proliferation and autoimmune disease. When we expanded CD98-null T cells in vitro, they adoptively transferred diabetes, establishing that impaired clonal expansion was responsible for protection from disease. Thus, the integrin-binding domain of CD98 is required for Ag-driven T cell clonal expansion in the pathogenesis of an autoimmune disease and may represent a useful therapeutic target.

Genotype-Phenotype correlations in multiple sclerosis: HLA genes influence disease severity inferred by 1HMR spectroscopy and MRI measures

Genetic susceptibility to multiple sclerosis (MS) is associated with the human leukocyte antigen (HLA) DRB1*1501 allele. Here we show a clear association between DRB1*1501 carrier status and four domains of disease severity in an investigation of genotype-phenotype associations in 505 robust, clinically well characterized MS patients evaluated cross-sectionally: (i) a reduction in the N-acetyl-aspartate (NAA) concentration within normal appearing white matter (NAWM) via (1)HMR spectroscopy (P = 0.025), (ii) an increase in the volume of white matter (WM) lesions utilizing conventional anatomical MRI techniques (1,127 mm(3); P = 0.031), (iii) a reduction in normalized brain parenchymal volume (nBPV) (P = 0.023), and (iv) impairments in cognitive function as measured by the Paced Auditory Serial Addition Test (PASAT-3) performance (Mean Z Score: DRB1*1501+: 0.110 versus DRB1*1501-: 0.048; P = 0.004). In addition, DRB1*1501+ patients had significantly more women (74% versus 63%; P = 0.009) and a younger mean age at disease onset (32.4 years versus 34.3 years; P = 0.025). Our findings suggest that DRB1*1501 increases disease severity in MS by facilitating the development of more T2-foci, thereby increasing the potential for irreversible axonal compromise and subsequent neuronal degeneration, as suggested by the reduction of NAA concentrations in NAWM, ultimately leading to a decline in brain volume. These structural aberrations may explain the significant differences in cognitive performance observed between DRB1*1501 groups. The overall goal of a deep phenotypic approach to MS is to develop an array of meaningful biomarkers to monitor the course of the disease, predict future disease behaviour, determine when treatment is necessary, and perhaps to more effectively recommend an available therapeutic intervention.

Identical TCR beta-chain rearrangements in streptococcal angina and skin lesions of patients with psoriasis vulgaris

Tonsillar infection with Streptococcus pyogenes may induce several nonsuppurative autoimmune sequelae. The precise pathogenetic mechanisms behind this clinically well-established association are still unresolved. Using TCR analysis, we sought to identify a link between streptococcal tonsillitis and the T cell-mediated autoimmune response in psoriasis. Three patients with streptococcal-induced psoriasis underwent tonsillectomy. Using size spectratyping and sequencing of TCR beta-chain variable region gene (TCRBV) rearrangements, we compared the TCR usage of psoriatic skin lesions, blood, tonsils, and tonsillar T cells fractionated according to the expression of the skin address in "cutaneous lymphocyte-associated Ag" (CLA). TCRBV-size spectratype analysis of the blood lymphocytes, tonsils, and the CLA-negative tonsillar T cells revealed largely unselected T cell populations. Instead, TCRBV gene families of the psoriatic lesions and skin-homing CLA-positive tonsillar T cells displayed highly restricted spectratypes. Sequencing of TCRBV cDNA identified various clonal TCRBV rearrangements within the psoriatic lesions that indicated Ag-driven T cell expansion. Several of these clonotypes were also detected within the tonsils and, in one of the patients, within the small subset of CLA-positive tonsillar T cells, suggesting that T cells from the same T cell clones were simultaneously present within skin and tonsillar tissue. Because after tonsillectomy psoriasis cleared in all three patients our observations indicate that T cells may connect psoriatic inflammation to streptococcal angina. They suggest that the chronic streptococcal immune stimulus within the tonsils could act as a source for pathogenic T cells in poststreptococcal disorders, and they may help to explain why eliminating this source with tonsillectomy may improve streptococcal-induced sequelae.

Fatigue associated with multiple sclerosis: diagnosis, impact and management

In patients with multiple sclerosis (MS) fatigue is the most common symptom and one of the most disabling features. As many as 40% have described it as the single most disabling symptom--a higher percentage than weakness, spasticity, motor problems, or bowel or bladder problems. The etiology and pathophysiology of MS-related fatigue remain unknown. Studies have failed to demonstrate an association between MS-related fatigue and the level of disability, clinical disease subtype, or gender, although recent data show an association between MS-related fatigue and depression and quality of life. Imaging studies using positron emission tomography suggest that fatigue in MS is related to hypometabolism of specific brain areas, including the frontal and subcortical circuits. The impact of fatigue on patient functioning and quality of life clearly warrants intervention. In addition to nonpharmacologic measures, such as exercise and energy conservation strategies, several pharmacologic agents have been evaluated for their ability to reduce MS-related fatigue, including amantadine, central nervous system stimulants (pemoline), and the novel wake-promoting agent modafinil.

Diagnostic role of tests for T cell receptor (TCR) genes

Rapid advances in molecular biological techniques have made it possible to study disease pathogenesis at a genomic level. T cell receptor (TCR) gene rearrangement is an important event in T cell ontogeny that enables T cells to recognise antigens specifically, and any dysregulation in this complex yet highly regulated process may result in disease. Using techniques such as Southern blot hybridisation, polymerase chain reaction, and flow cytometry it has been possible to characterise T cell proliferations in malignancy and in diseases where T cells have been implicated in the pathogenesis. The main aim of this article is to discuss briefly the process of TCR gene rearrangement and highlight the disorders in which expansions or clonal proliferations of T cells have been recognised. It will also describe various methods that are currently used to study T cell populations in body fluids and tissue, their diagnostic role, and current limitations of the methodology.

Aberrant T cell responses to myelin antigens during clinical exacerbation in patients with multiple sclerosis

Multiple sclerosis (MS) is a demyelinating disease of presumed T cell autoimmunity against self myelin. We hypothesized that if myelin-reactive T cells are associated with the disease processes, they may undergo activation and expansion during acute exacerbation. In this study, we examined the precursor frequency, epitope recognition and cytokine profile of myelin-reactive T cells in 14 relapsing/remitting MS patients during exacerbation and remission. The study revealed that T cells recognizing the immunodominant peptides of candidate myelin antigens, including myelin basic protein (MBP), proteolipid protein and myelin oligodendrocyte glycoprotein, occurred at increased precursor frequency during acute exacerbation. The T cell responses to MBP focused on the immunodominant regions (residues 83-99 and 151-170) during exacerbation and shifted toward other epitopes of MBP at the time of remission. Furthermore, there was a marked increase in the production of T(h)1 cytokines among T cell lines obtained during exacerbation compared to those obtained during remission. The study demonstrated that myelin-reactive T cells underwent selective activation and expansion during acute MS exacerbation. In contrast, myelin-reactive T cells found during remission in the same patients generally resembled those identified in healthy controls with some discrepancies. The findings suggest potential association of aberrant myelin-reactive T cell responses with acute exacerbation in MS, which may reflect transient activation of myelin-reactive T cell populations of pathogenic potential.

Evidence of T cell receptor beta-chain patterns in inflammatory and noninflammatory bowel disease states

T cell activation, as defined by expression of relevant cell surface molecules, such as the interleukin-2 receptor (CD25), is increased in many chronic relapsing diseases, including inflammatory bowel disease (IBD). These T cells are generally activated through contact of their clonotypic T cell receptor (TCR) with a peptide antigen presented by a major histocompatibility complex molecule. One of the putative antigenic contact sites for the TCR is the third complementarity determining region (CDR3) of the TCR beta-chain variable region (TCRBV). Therefore, analysis of the TCRBV CDR3 provides insight into the diversity of antigens encountered by a given T cell population. This study evaluated the TCRBV CDR3 usage of the activated intestinal lymphocytes from human subjects with IBD, diverticulitis (inflammatory control), and a normal tissue control. Public patterns, as demonstrated by shared TCRBV CDR3 amino acid sequences of activated intestinal T cell subpopulations, were observed. In particular, a public pattern of TCRBV22, a conserved valine in the fifth position, and use of TCRBJ2S1 or TCRBJ2S5 was present in three of four Crohn's disease subjects while not present in the ulcerative colitis subjects. However, the private patterns of TCRBV CDR3 region amino acid sequences were far more striking and easily demonstrated in all individuals studied, including a normal noninflammatory control. Thus we conclude that selective antigenic pressures are prevalent among an individual's activated intestinal lymphocytes.

Recommendations for physical activity in patients with multiple sclerosis

For many years, patients with multiple sclerosis (MS), an inflammatory demyelinating disease of the central nervous system, have been advised to avoid exercise. MS is believed to be autoimmune in origin, mediated by activated T cells which penetrate the blood-brain barrier and attack myelin. The pathophysiology, with respect to function is an impairment of saltatory conduction, specifically, slowing of conduction speed and/or conduction block. Symptoms can temporarily worsen on exposure to heat or during physical exercise. Exercise programmes must be designed to activate working muscles but avoid overload that results in conduction block. Fatigue, often severe, affects about 85% of MS patients and, along with motor and sensory symptoms, results in decreased mobility and reduced quality of life. Physical activity and recreation are reduced in patients with MS. Before developing recommendations, physical activity patterns and the physical effects of MS should be assessed in individual patients. Patients may then be functionally classified. Physical activity can also be classified in a pyramid structure, with the most basic functions forming the base and the most integrated functions on top. The muscular fitness pyramid progresses through passive range of motion, active resistive, specific strengthening and integrated strength exercises Overall physical activity may be increased according to functional level by performing activities of daily living, incorporating inefficiencies into daily living, pursuing more active recreation and eventually developing a structured exercise programme. The importance of the proper exercise environment, balance and coordination issues and factors related to adherence are discussed.

A functional link for major TCR expansions in healthy adults caused by persistent Epstein-Barr virus infection

Dramatic clonal expansions of unknown functional significance have been documented in the T cell receptor (TCR) alpha beta peripheral blood repertoires of apparently healthy adults. In this study, we provide evidence that persistent infection with the ubiquitous Epstein-Barr virus (EBV) causes major distortions within the memory repertoire of healthy virus carriers. Using complementarity determining region 3 (CDR3) length analysis to measure repertoire diversity, dominant expansions that dramatically skewed the entire TCRBV6 blood repertoire towards oligoclonality were enriched in the CD8(+)CD45RO+CD45RA- subset of HLA B8(+) healthy virus carriers. Evidence of phenotypic heterogeneity between individuals was also observed for these expansions based on their variable coexpression of CD45RO and CD45RA. TCR junctional region sequencing revealed that these expansions were clonal and that they represented commonly selected HLA B8-restricted memory cytotoxic T cells that recognize the immunodominant latent EBV epitope, FLRGRAYGL. Furthermore, the functional identity of these virus-specific CD8(+) T cells was confirmed by their FLRGRAYGL-specific cytotoxicity. Therefore, the functional significance of dramatic clonal expansions in healthy adults can be linked in some cases to virus-specific CD8(+) T cells that play an essential role in immunosurveillance. This first identified link for expansions in the circulation of healthy adults strongly implies that restricted-memory TCR responses to environmental antigens play a pivotal role in expansion development, which should have an important impact on studies interpreting TCR expansion patterns in health and disease.

Idiosyncratic alterations of TCR size distributions affecting both CD4 and CD8 T cell subsets in aging mice

We have used a spectratyping method, which displays the size distribution for the complementarity-determining region 3 (CDR3) for T cells utilizing a specific TCR-Vbeta gene, to examine the effects of aging on the TCR repertoire of (BALB/c x C57BL/6)F1 hybrid mice. Although the size distributions from T cells of 8-month-old mice were typically symmetrically shaped around one or two bands of intermediate size, spectratypes from mice 16 or 24 months of age were frequently distorted, with specific size classes either over- or underrepresented compared to normal young controls. Each of 12 mice tested at 16 or 24 months of age had a skewed spectratype for at least one of the 24 Vbeta families examined, and some mice had more than 50% of their spectratypes skewed significantly, as judged by a chi2 test. Comparable age-associated skewing of the T cell repertoire occurred in the CD4 and CD8 subsets, and every mouse over 16 months of age exhibited at least one skewed Vbeta family in both the CD4 and CD8 populations. Although the mice were genetically identical and raised in common facilities, their spectratype patterns were nonetheless idiosyncratic: i.e., the specific set of abnormalities was distinct for each individual old mouse. Whether these distortions of the TCR repertoire in middle-aged and older mice lead to alterations in immune function remains to be determined.

Effective treatment of models of multiple sclerosis by matrix metalloproteinase inhibitors

The proinflammatory Th1 cytokine, tumor necrosis factor-alpha (TNF alpha), the cell death signaling molecule FasL, and several extracellular matrix degrading metalloproteinases have been implicated in the pathogenesis of multiple sclerosis (MS). The latter enzymes, as well as TNF alpha-converting enzyme and FasL-converting enzyme, can be blocked by matrix metalloproteinase inhibitors (MMPIs). In this study, we show that a potent MMPI was clinically effective in an animal model for MS, experimental autoimmune encephalomyelitis (EAE) in the SJL/J mouse. Efficacy was remarkable, as indicated by blocking and reversal of acute disease and reduced number of relapses and diminished mean cumulative disease score in chronic relapsing animals. Also, demyelination and glial scarring were significantly decreased in MMPI-treated mice with chronic relapsing EAE, as was central nervous system gene expression for TNF alpha and fasL. It is interesting that expression of the beneficial cytokine interleukin-4 (IL-4) was increased, and IL-4 was expressed on glial cells. The relevance of these compounds for MS was underscored by their ability to specifically inhibit TNF alpha shedding and cytotoxicity of myelin-autoreactive human cytotoxic CD4+ T-cell clones. This is the first report to show a positive effect by MMPIs on chronic relapsing EAE, its central nervous system cytokine profile, and on TNF alpha shedding by human myelin-autoreactive T cells.

Non-MHC-Restricted Cell-Mediated Lysis of Human Oligodendrocytes In Vitro: Relation with CD56 Expression

Oligodendrocytes and their myelin membranes are the apparent target of the autoimmune response that characterizes the human adult central nervous system-demyelinating disease multiple sclerosis. Human oligodendrocytes do not express MHC class II molecules, a requirement for MHC-restricted injury mediated by myelin-reactive CD4+ T cells, the cell type implicated in initiating the disease process. In this study we observed that human adult central nervous system-derived oligodendrocytes can be susceptible to non-MHC-restricted lysis mediated by myelin basic protein-reactive CD4+ T cell lines. Cytotoxicity was significantly greater (37 ± 4 vs 7 ± 3%) with cell lines in which a high proportion of cells (mean, 28 ± 6%) expressed CD56 compared with cytotoxicity mediated by low CD56 cell lines (8 ± 2%). High CD56 cell lines, when rested in IL-2, lost cytotoxic activity and had reduced expression of CD56 (mean, 5 ± 2%). CD4+ T cells isolated from short term (3-day) anti-CD3/IL-2-activated mononuclear cell cultures did not express CD56 and were not cytotoxic to oligodendrocytes unless lectin was added. In contrast, an enriched population of non-T cells extracted from the same activated MNC cultures expressed CD56 as well as other NK cell-associated surface molecules and was cytotoxic. These results indicate the potential susceptibility of human oligodendrocytes to non-MHC-restricted injury mediated by both Ag-reactive and nonspecific cellular immune effector cells, with CD56 expression being a common feature of the effector cells.

Use of T cell receptor/HLA-DRB1*04 molecular modeling to predict site-specific interactions for the DR shared epitope associated with rheumatoid arthritis

OBJECTIVE

To use molecular modeling tools to analyze the potential structural basis for the genetic association of rheumatoid arthritis (RA) with the major histocompatibility complex (MHC) "shared epitope," a set of conserved amino acid residues in the third hypervariable region of the DRbeta chain.

METHODS

Homology model building techniques were used to construct molecular models of the arthritis-associated DRB1*0404 molecule and a T cell receptor (TCR) from T cell clone EM025, which is specific for DR4 molecules containing the shared epitope sequence. Interactive graphics techniques were used to orient the TCR on the DR molecule, guided by surface complementarity analysis.

RESULTS

The predicted TCR-MHC-peptide complex involved multiple interactions and specificity for the shared epitope. TCR residues CDR1beta D30, CDR2beta N51, and CDR3beta Q97 were positioned to potentially participate in hydrogen bond interactions with the shared epitope DRbeta residues Q70 and R71.

CONCLUSION

These results suggest a structural mechanism in which specific TCR recognition and possibly Vbeta selection are directly influenced by the disease-associated MHC polymorphisms.

Pathogenesis of immune-mediated demyelination in the CNS

Collective evidence from studies in the animal model experimental autoimmune encephalomyelitis and pathological and immunological studies on MS patients suggest that this most common inflammatory demyelinating disorder of the central nervous system results from primarily T-lymphocyte driven aberrant immune responses to a number of myelin and possibly non-myelin antigens. These include MBP, PLP, MOG, MAG, CNP and S 100. Autoreactive T-cells reactive with these antigens circulate in blood and upon activation can travel across the blood-brain-barrier to initiate a local immunoflammatory response provided they encounter a microglial cell that displays antigenic epitopes in the context of MHC class II gene products and accessory molecules. Demyelination probably results from antibody-induced complement activation. Repeated inflammatory episodes eventually exhaust the reparative capacities of oligodendrocytes and damage axons. As the disease evolves, an initialy focussed immune response may diversify due to a process termed epitope spreading. The initial event of T lymphocyte activation remains elusive, but molecular mimicry, cross-recognition of structures shared between microbes and myelin, appears to be crucial.

B7-mediated costimulation and the immune response

In addition to presentation of antigen, T cells require additional or 'costimulatory' signals from antigen-presenting cells. Failure to receive costimulation following antigen presentation renders T cells anergic, and these cells are functionally incapable of proliferating or secreting cytokines in response to subsequent rechallenge. Recent evidence has demonstrated that a critical costimulatory signal is delivered by members of the B7 family. B7-1 (CD80) and B7-2 (CD86) provide costimulation through CD28, their ligand on the T cell. Dysregulation of expression of B7 may be implicated in the pathogenesis of autoimmune disease. In contrast, lack of expression of B7 on tumor cells may explain in part the lack of immune response against the majority of tumors. It may now be possible to exploit this pathway to induce immunological response against tumors. Blockade of this pathway will likely have significant impact on transplantation biology, to induce T-cell anergy and prevent graft rejection and graft-versus-host disease.