Receptor revision and atypical mutational characteristics in clonally expanded B cells from the cerebrospinal fluid of recently diagnosed multiple sclerosis patients

Molecular biomarkers in multiple sclerosis

Multiple sclerosis (MS) is a highly heterogenous disease regarding radiological, pathological, and clinical characteristics and therapeutic response, including both the efficacy and safety profile of treatments. Accordingly, there is a high demand for biomarkers that sensitively and specifically apprehend the distinctive aspects of the MS heterogeneity, and that can aid in better understanding of the disease diagnosis, prognosis, prediction of the treatment response, and, finally, in the development of new treatments. Currently, clinical characteristics (e.g., relapse rate and disease progression) and magnetic resonance imaging play the most important role in the clinical classification of MS and assessment of its course. Molecular biomarkers (e.g., immunoglobulin G (IgG) oligoclonal bands, IgG index, anti-aquaporin-4 antibodies, neutralizing antibodies against interferon-beta and natalizumab, anti-varicella zoster virus and anti-John Cunningham (JC) virus antibodies) complement these markers excellently. This review provides an overview of exploratory, validated and clinically useful molecular biomarkers in MS which are used for prediction, diagnosis, disease activity and treatment response.

Next Generation Sequencing of Cerebrospinal Fluid B Cell Repertoires in Multiple Sclerosis and Other Neuro-Inflammatory Diseases-A Comprehensive Review

During the last few decades, the role of B cells has been well established and redefined in neuro-inflammatory diseases, including multiple sclerosis and autoantibody-associated diseases. In particular, B cell maturation and trafficking across the blood–brain barrier (BBB) has recently been deciphered with the development of next-generation sequencing (NGS) approaches, which allow the assessment of representative cerebrospinal fluid (CSF) and peripheral blood B cell repertoires. In this review, we perform literature research focusing on NGS studies that allow further insights into B cell pathophysiology during neuro-inflammation. Besides the analysis of CSF B cells, the paralleled assessment of peripheral blood B cell repertoire provides deep insights into not only the CSF compartment, but also in B cell trafficking patterns across the BBB. In multiple sclerosis, CSF-specific B cell maturation, in combination with a bidirectional exchange of B cells across the BBB, is consistently detectable. These data suggest that B cells most likely encounter antigen(s) within the CSF and migrate across the BBB, with further maturation also taking place in the periphery. Autoantibody-mediated diseases, such as neuromyelitis optica spectrum disorder and LGI1 / NMDAR encephalitis, also show features of a CSF-specific B cell maturation and clonal connectivity with peripheral blood. In conclusion, these data suggest an intense exchange of B cells across the BBB, possibly feeding autoimmune circuits. Further developments in sequencing technologies will help to dissect the exact pathophysiologic mechanisms of B cells during neuro-inflammation.

Association of cerebrospinal fluid kappa free light chains with the intrathecal polyspecific antiviral immune response in multiple sclerosis

The polyspecific B-lymphocyte response to neurotropic viruses such as measles (M), rubella (R) and varicella zoster (Z), known as MRZ reaction, is to-date the most specific neurochemical marker for multiple sclerosis (MS). The aim of this study was to investigate a possible association of immunoglobulin (Ig) kappa (κ-) and lambda (λ-) free light chains (FLC) with the presence of the MRZ reaction in multiple sclerosis. Immunoglobulin κ- and λ-FLC, MRZ reaction, oligoclonal IgG bands (OCB), and cerebrospinal fluid (CSF) routine parameters were measured in 65 MS patients. OCB were detected in 97% of MS patients, intrathecal IgG synthesis according to Reiber was detectable in 57%, an elevated IgG index (>0.7) in 66% and the MRZR was positive in 45%. All investigated κ-values (CSF κFLC, CSF-serum ratio of κFLCs (QκFLC), and κFLC index (κFLC/QAlbumin)) were significantly higher in patients with positive MRZ reaction as compared to MRZ negative MS patients. In contrast, λ-values showed no significant differences. Additionally to the putative diagnostic sensitivity and prognostic value of κFLC, the association of κFLC with a highly specific neurochemical marker for MS - the MRZ reaction, especially the determination of κFLCs is an informative tool to assess the B-cell response and determine its extent in MS patients.

Evidence of Alternative Modes of B Cell Activation Involving Acquired Fab Regions of N-Glycosylation in Antibody-Secreting Cells Infiltrating the Labial Salivary Glands of Patients With Sjögren's Syndrome

OBJECTIVE

To better understand the role of B cells, the potential mechanisms responsible for their aberrant activation, and the production of autoantibodies in the pathogenesis of Sjögren's syndrome (SS), this study explored patterns of selection pressure and sites of N-glycosylation acquired by somatic mutation (acN-glyc) in the IgG variable (V) regions of antibody-secreting cells (ASCs) isolated from the minor salivary glands of patients with SS and non-SS control patients with sicca symptoms.

METHODS

A novel method to produce and characterize recombinant monoclonal antibodies (mAb) from single cell-sorted ASC infiltrates was applied to concurrently probe expressed genes (all heavy- and light-chain isotypes as well as any other gene of interest not related to immunoglobulin) in the labial salivary glands of patients with SS and non-SS controls. V regions were amplified by reverse transcription-polymerase chain reaction, sequenced, and analyzed for the incidence of N-glycosylation and selection pressure. For specificity testing, the amplified regions were expressed as either the native mAb or mutant mAb lacking the acN-glyc motif. Protein modeling was used to demonstrate how even an acN-glyc site outside of the complementarity-determining region could participate in, or inhibit, antigen binding.

RESULTS

V-region sequence analyses revealed clonal expansions and evidence of secondary light-chain editing and allelic inclusion, of which neither of the latter two have previously been reported in patients with SS. Increased frequencies of acN-glyc were found in the sequences from patients with SS, and these acN-glyc regions were associated with an increased number of replacement mutations and lowered selection pressure. A clonal set of polyreactive mAb with differential framework region 1 acN-glyc motifs was also identified, and removal of the acN-glyc could nearly abolish binding to autoantigens.

CONCLUSION

These findings support the notion of an alternative mechanism for the selection and proliferation of some autoreactive B cells, involving V-region N-glycosylation, in patients with SS.

In Silico Prediction Analysis of Idiotope-Driven T-B Cell Collaboration in Multiple Sclerosis

Memory B cells acting as antigen-presenting cells are believed to be important in multiple sclerosis (MS), but the antigen they present remains unknown. We hypothesized that B cells may activate CD4⁺ T cells in the central nervous system of MS patients by presenting idiotopes from their own immunoglobulin variable regions on human leukocyte antigen (HLA) class II molecules. Here, we use bioinformatics prediction analysis of B cell immunoglobulin variable regions from 11 MS patients and 6 controls with other inflammatory neurological disorders (OINDs), to assess whether the prerequisites for such idiotope-driven T–B cell collaboration are present. Our findings indicate that idiotopes from the complementarity determining region (CDR) 3 of MS patients on average have high predicted affinities for disease associated HLA-DRB1*15:01 molecules and are predicted to be endosomally processed by cathepsin S and L in positions that allows such HLA binding to occur. Additionally, complementarity determining region 3 sequences from cerebrospinal fluid (CSF) B cells from MS patients contain on average more rare T cell-exposed motifs that could potentially escape tolerance and stimulate CD4⁺ T cells than CSF B cells from OIND patients. Many of these features were associated with preferential use of the IGHV4 gene family by CSF B cells from MS patients. This is the first study to combine high-throughput sequencing of patient immune repertoires with large-scale prediction analysis and provides key indicators for future in vitro and in vivo analyses.

Peripheral VH4+ plasmablasts demonstrate autoreactive B cell expansion toward brain antigens in early multiple sclerosis patients

Plasmablasts are a highly differentiated, antibody secreting B cell subset whose prevalence correlates with disease activity in Multiple Sclerosis (MS). For most patients experiencing partial transverse myelitis (PTM), plasmablasts are elevated in the blood at the first clinical presentation of disease (known as a clinically isolated syndrome or CIS). In this study we found that many of these peripheral plasmablasts are autoreactive and recognize primarily gray matter targets in brain tissue. These plasmablasts express antibodies that over-utilize immunoglobulin heavy chain V-region subgroup 4 (VH4) genes, and the highly mutated VH4+ plasmablast antibodies recognize intracellular antigens of neurons and astrocytes. Most of the autoreactive, highly mutated VH4+ plasmablast antibodies recognize only a portion of cortical neurons, indicating that the response may be specific to neuronal subgroups or layers. Furthermore, CIS-PTM patients with this plasmablast response also exhibit modest reactivity toward neuroantigens in the plasma IgG antibody pool. Taken together, these data indicate that expanded VH4+ peripheral plasmablasts in early MS patients recognize brain gray matter antigens. Peripheral plasmablasts may be participating in the autoimmune response associated with MS, and provide an interesting avenue for investigating the expansion of autoreactive B cells at the time of the first documented clinical event.

Assessment of Intrathecal Free Light Chain Synthesis: Comparison of Different Quantitative Methods with the Detection of Oligoclonal Free Light Chains by Isoelectric Focusing and Affinity-Mediated Immunoblotting

Objectives

We aimed to compare various methods for free light chain (fLC) quantitation in cerebrospinal fluid (CSF) and serum and to determine whether quantitative CSF measurements could reliably predict intrathecal fLC synthesis. In addition, we wished to determine the relationship between free kappa and free lambda light chain concentrations in CSF and serum in various disease groups.

Methods

We analysed 166 paired CSF and serum samples by at least one of the following methods: turbidimetry (Freelite™, SPA_PLUS), nephelometry (N Latex FLC™, BN ProSpec), and two different (commercially available and in-house developed) sandwich ELISAs. The results were compared with oligoclonal fLC detected by affinity-mediated immunoblotting after isoelectric focusing.

Results

Although the correlations between quantitative methods were good, both proportional and systematic differences were discerned. However, no major differences were observed in the prediction of positive oligoclonal fLC test. Surprisingly, CSF free kappa/free lambda light chain ratios were lower than those in serum in about 75% of samples with negative oligoclonal fLC test. In about a half of patients with multiple sclerosis and clinically isolated syndrome, profoundly increased free kappa/free lambda light chain ratios were found in the CSF.

Conclusions

Our results show that using appropriate method-specific cut-offs, different methods of CSF fLC quantitation can be used for the prediction of intrathecal fLC synthesis. The reason for unexpectedly low free kappa/free lambda light chain ratios in normal CSFs remains to be elucidated. Whereas CSF free kappa light chain concentration is increased in most patients with multiple sclerosis and clinically isolated syndrome, CSF free lambda light chain values show large interindividual variability in these patients and should be investigated further for possible immunopathological and prognostic significance.

High-Density Peptide Microarray Analysis of IgG Autoantibody Reactivities in Serum and Cerebrospinal Fluid of Multiple Sclerosis Patients

Intrathecal immunoglobulin G (IgG) synthesis and oligoclonal IgG bands in cerebrospinal fluid (CSF) are hallmarks of multiple sclerosis (MS), but the antigen specificities remain enigmatic. Our study is the first investigating the autoantibody repertoire in paired serum and CSF samples from patients with relapsing-remitting MS (RRMS), primary progressive MS (PPMS), and other neurological diseases by the use of high-density peptide microarrays. Protein sequences of 45 presumed MS autoantigens (e.g.MOG, MBP, and MAG) were represented on the microarrays by overlapping 15mer peptides. IgG reactivities were screened against a total of 3991 peptides, including also selected viral epitopes. The measured antibody reactivities were highly individual but correlated for matched serum and CSF samples. We found 54 peptides to be recognized significantly more often by serum or CSF antibodies from MS patients compared with controls (pvalues <0.05). The results for RRMS and PPMS clearly overlapped. However, PPMS patients presented a broader peptide-antibody signature. The highest signals were detected for a peptide mapping to a region of the Epstein-Barr virus protein EBNA1 (amino acids 392-411), which is homologous to the N-terminal part of human crystallin alpha-B. Our data confirmed several known MS-associated antigens and epitopes, and they delivered additional potential linear epitopes, which await further validation. The peripheral and intrathecal humoral immune response in MS is polyspecific and includes antibodies that are also found in serum of patients with other diseases. Further studies are required to assess the pathogenic relevance of autoreactive and anti-EBNA1 antibodies as well as their combinatorial value as biomarkers for MS.

B Cells Are Multifunctional Players in Multiple Sclerosis Pathogenesis: Insights from Therapeutic Interventions

Multiple sclerosis (MS) is a severe disease of the central nervous system (CNS) characterized by autoimmune inflammation and neurodegeneration. Historically, damage to the CNS was thought to be mediated predominantly by activated pro-inflammatory T cells. B cell involvement in the pathogenesis of MS was solely attributed to autoantibody production. The first clues for the involvement of antibody-independent B cell functions in MS pathology came from positive results in clinical trials of the B cell-depleting treatment rituximab in patients with relapsing-remitting (RR) MS. The survival of antibody-secreting plasma cells and decrease in T cell numbers indicated the importance of other B cell functions in MS such as antigen presentation, costimulation, and cytokine production. Rituximab provided us with an example of how clinical trials can lead to new research opportunities concerning B cell biology. Moreover, analysis of the antibody-independent B cell functions in MS has gained interest since these trials. Limited information is present on the effects of current immunomodulatory therapies on B cell functions, although effects of both first-line (interferon, glatiramer acetate, dimethyl fumarate, and teriflunomide), second-line (fingolimod, natalizumab), and even third-line (monoclonal antibody therapies) treatments on B cell subtype distribution, expression of functional surface markers, and secretion of different cytokines by B cells have been studied to some extent. In this review, we summarize the effects of different MS-related treatments on B cell functions that have been described up to now in order to find new research opportunities and contribute to the understanding of the pathogenesis of MS.

MSPrecise: A molecular diagnostic test for multiple sclerosis using next generation sequencing

BACKGROUND

We have previously demonstrated that cerebrospinal fluid-derived B cells from early relapsing-remitting multiple sclerosis (RRMS) patients that express a VH4 gene accumulate specific replacement mutations. These mutations can be quantified as a score that identifies such patients as having or likely to convert to RRMS. Furthermore, we showed that next generation sequencing is an efficient method for obtaining the sequencing information required by this mutation scoring tool, originally developed using the less clinically viable single-cell Sanger sequencing.

OBJECTIVE

To determine the accuracy of MSPrecise, the diagnostic test that identifies the presence of the RRMS-enriched mutation pattern from patient cerebrospinal fluid B cells.

METHODS

Cerebrospinal fluid cell pellets were obtained from RRMS and other neurological disease (OND) patient cohorts. VH4 gene segments were amplified, sequenced by next generation sequencing and analyzed for mutation score.

RESULTS

The diagnostic test showed a sensitivity of 75% on the RRMS cohort and a specificity of 88% on the OND cohort. The accuracy of the test in identifying RRMS patients or patients that will develop RRMS is 84%.

CONCLUSION

MSPrecise exhibits good performance in identifying patients with RRMS irrespective of time with RRMS.

The Ins and Outs of B Cells in Multiple Sclerosis

B cells play a central role in multiple sclerosis (MS) pathology. B and plasma cells may contribute to disease activity through multiple mechanisms: antigen presentation, cytokine secretion, or antibody production. Molecular analyses of B cell populations in MS patients have revealed significant overlaps between peripheral lymphoid and clonally expanded central nervous system (CNS) B cell populations, indicating that B cell trafficking may play a critical role in driving MS exacerbations. In this review, we will assess our current knowledge of the mechanisms and pathways governing B cell migration into the CNS and examine evidence for and against a compartmentalized B cell response driving progressive MS pathology.

A Distinct Class of Antibodies May Be an Indicator of Gray Matter Autoimmunity in Early and Established Relapsing Remitting Multiple Sclerosis Patients

*These authors contributed equally to the work in this manuscript.We have previously identified a distinct class of antibodies expressed by B cells in the cerebrospinal fluid (CSF) of early and established relapsing remitting multiple sclerosis (RRMS) patients that is not observed in healthy donors. These antibodies contain a unique pattern of mutations in six codons along VH4 antibody genes that we termed the antibody gene signature (AGS). In fact, patients who have such B cells in their CSF are identified as either having RRMS or developing RRMS in the future. As mutations in antibody genes increase antibody affinity for particular antigens, the goal for this study was to investigate whether AGS(+) antibodies bind to brain tissue antigens. Single B cells were isolated from the CSF of 10 patients with early or established RRMS. We chose 32 of these B cells that expressed antibodies enriched for the AGS for further study. We generated monoclonal full-length recombinant human antibodies (rhAbs) and used both immunological assays and immunohistochemistry to investigate the capacity of these AGS(+) rhAbs to bind brain tissue antigens. AGS(+) rhAbs did not recognize myelin tracts in the corpus callosum. Instead, AGS(+) rhAbs recognized neuronal nuclei and/or astrocytes, which are prevalent in the cortical gray matter. This pattern was unique to the AGS(+) antibodies from early and established RRMS patients, as AGS(+) antibodies from an early neuromyelitis optica patient did not display the same reactivity. Prevalence of CSF-derived B cells expressing AGS(+) antibodies that bind to these cell types may be an indicator of gray matter-directed autoimmunity in early and established RRMS patients.

Antigen Presentation, Autoantigens, and Immune Regulation in Multiple Sclerosis and Other Autoimmune Diseases

Antigen presentation is in the center of the immune system, both in host defense against pathogens, but also when the system is unbalanced and autoimmune diseases like multiple sclerosis (MS) develop. It is not just by chance that a major histocompatibility complex gene is the major genetic susceptibility locus in MS; a feature that MS shares with other autoimmune diseases. The exact etiology of the disease, however, has not been fully understood yet. T cells are regarded as the major players in the disease, but most probably a complex interplay of altered central and peripheral tolerance mechanisms, T-cell and B-cell functions, characteristics of putative autoantigens, and a possible interference of environmental factors like microorganisms are at work. In this review, new data on all these different aspects of antigen presentation and their role in MS will be discussed, probable autoantigens will be summarized, and comparisons to other autoimmune diseases will be drawn.

Intrathecal BCR transcriptome in multiple sclerosis versus other neuroinflammation: Equally diverse and compartmentalized, but more mutated, biased and overlapping with the proteome

The mechanisms driving the intrathecal synthesis of IgG in multiple sclerosis (MS) are unknown. We combined high-throughput sequencing of transcribed immunoglobulin heavy-chain variable (IGHV) genes and mass spectrometry to chart the diversity and compartmentalization of IgG-producing B cells in the cerebrospinal fluid (CSF) of MS patients and controls with other neuroinflammatory diseases. In both groups, a few clones dominated the intrathecal IGHV transcriptome. In most MS patients and some controls, dominant transcripts matched the CSF IgG. The IGHV transcripts in CSF of MS patients frequently carried IGHV4 genes and had more replacement mutations compared to controls. In both groups, dominant IGHV transcripts were identified within clusters of clonally related B cells that had identical or related IGHV transcripts in the blood. These findings suggest more pronounced affinity maturation, but an equal degree of diversity and compartmentalization of the intrathecal B-cell response in MS compared to other neuroinflammatory diseases.

Capillary isoelectric focusing immunoassay as a new nanoscale approach for the detection of oligoclonal bands

The detection of oligoclonal bands (OCBs) in cerebrospinal fluid is an indicator of intrathecal synthesis of immunoglobulins which is a neurochemical sign of chronic inflammatory brain diseases. Intrathecally synthesized IgGs are typically observed in patients with multiple sclerosis. The current standard protocol for the detection of OCBs is IEF on agarose or polyacrylamide gels followed by immunoblotting or silver staining. These methods are time consuming, show substantial interlaboratory variation and cannot be used in a high throughput-approach. We have developed a new nanoscale method for the detection of OCBs based on automated capillary IEF followed by immunological detection. Evidence for intrathecal IgG synthesis was found in all tested patients (n = 27) with multiple sclerosis, even in two subjects who did not have oligoclonal bands according to standard methods. The test specificity was at 97.5% (n = 19). Our findings indicate that the novel OCB-CIEF-immunoassay is suitable for the rapid and highly sensitive detection of OCBs in clinical samples. Furthermore, the method allows for a higher sample throughput than the current standard methods.

The antibody genetics of multiple sclerosis: comparing next-generation sequencing to sanger sequencing

We previously identified a distinct mutation pattern in the antibody genes of B cells isolated from cerebrospinal fluid (CSF) that can identify patients who have relapsing-remitting multiple sclerosis (RRMS) and patients with clinically isolated syndromes who will convert to RRMS. This antibody gene signature (AGS) was developed using Sanger sequencing of single B cells. While potentially helpful to patients, Sanger sequencing is not an assay that can be practically deployed in clinical settings. In order to provide AGS evaluations to patients as part of their diagnostic workup, we developed protocols to generate AGS scores using next-generation DNA sequencing (NGS) on CSF-derived cell pellets without the need to isolate single cells. This approach has the potential to increase the coverage of the B-cell population being analyzed, reduce the time needed to generate AGS scores, and may improve the overall performance of the AGS approach as a diagnostic test in the future. However, no investigations have focused on whether NGS-based repertoires will properly reflect antibody gene frequencies and somatic hypermutation patterns defined by Sanger sequencing. To address this issue, we isolated paired CSF samples from eight patients who either had MS or were at risk to develop MS. Here, we present data that antibody gene frequencies and somatic hypermutation patterns are similar in Sanger and NGS-based antibody repertoires from these paired CSF samples. In addition, AGS scores derived from the NGS database correctly identified the patients who initially had or subsequently converted to RRMS, with precision similar to that of the Sanger sequencing approach. Further investigation of the utility of the AGS in predicting conversion to MS using NGS-derived antibody repertoires in a larger cohort of patients is warranted.

Intrathecal oligoclonal IgG synthesis in multiple sclerosis

The diagnosis of multiple sclerosis is based on dissemination in time and space. Before 2010 lack of evidence for dissemination in space could be substituted by a paraclinical test, cerebrospinal fluid (CSF) oligoclonal bands (OCBs). The present meta-analysis (13,467 patients) shows that the diagnostic specificity of OCB drops from 94% to 61% if inflammatory etiologies are considered. Importantly, this was not caused by poor laboratory practice. This review on CSF OCB further illustrates the conceptional problem of substituting dissemination in space with a biomarker. The potential prognostic value of intrathecal OCB will need to be tested prospectively.

Expansion of CD27high plasmablasts in transverse myelitis patients that utilize VH4 and JH6 genes and undergo extensive somatic hypermutation

Patients with the autoimmune disease multiple sclerosis (MS) typically present with the clinically isolated syndromes (CIS) transverse myelitis (TM) or optic neuritis (ON). B-cell disturbances have been well documented in patients with MS and CIS patients with ON, but not in CIS patients with TM, despite the fact that these patients have the worst clinical outcome of all CIS types. The goal of this study was to characterize the B-cell populations and immunoglobulin genetics in TM patients. We found a unique expansion of CD27(high) plasmablasts in both the cerebrospinal fluid and periphery of TM patients that is not present in ON patients. Additionally, plasmablasts from TM patients show evidence for positive selection with increased somatic hypermutation accumulation in VH4(+) B cells and receptor editing that is not observed in ON patients. These characteristics unique to TM patients may impact disease severity and progression.

Pathogenesis of multiple sclerosis: what can we learn from the cuprizone model

Multiple sclerosis is an inflammatory demyelinating and neurodegenerative disorder of the central nervous system (CNS). The primary cause of the disease remains unknown, but an altered immune regulation with features of autoimmunity has generally been considered to play a critical role in the pathogenesis. Historically, lesion development has been attributed to activation of CD4 and CD8 T lymphocytes, B lymphocytes, and monocytes in the peripheral circulation and the migration of these cells through the blood-brain barrier to exert direct or indirect cytotoxic effects on myelin, oligodendrocytes and neuronal processes in the CNS. This broadly accepted concept was significantly influenced by the experimental autoimmune encephalitis (EAE) model, in which either immunization with myelin antigens or injection of a myelin antigen-specific T cell line into a recipient results in inflammatory demyelination in the CNS. More recent studies reveal that the loss of oligodendrocytes and neurons begins in the earliest stages of the disease and may not always be associated with blood-derived inflammatory cells. The pathology affects both the white and the gray matters and the clinical disability best correlates with the overall neurodegenerative process. These newer observations prompted several revisions of the classical concept of MS and facilitated a shift from using EAE to using other model systems. This chapter summarizes the classical and more contemporary concepts of MS, and provides methodologies for employing the cuprizone model for further explorations of the pathogenesis and treatment of the disease.

Related B cell clones that populate the CSF and CNS of patients with multiple sclerosis produce CSF immunoglobulin

We investigated the overlap shared between the immunoglobulin (Ig) proteome of the cerebrospinal fluid (CSF) and the B cell Ig-transcriptome of CSF and the central nervous system (CNS) tissue of three patients with multiple sclerosis. We determined the IgG-proteomes of CSF by mass spectrometry, and compared them to the IgG-transcriptomes from CSF and brain lesions, which were analyzed by cDNA cloning. Characteristic peptides that were identified in the CSF-proteome could also be detected in the transcriptomes of both, brain lesions and CSF, providing evidence for a strong overlap of the IgG repertoires in brain lesions and in the CSF.

The cellular prion protein in multiple sclerosis: A potential target for neurotherapeutics?

Multiple sclerosis (MS) is a debilitating disease that affects millions. There is no known cure for the disease and neither is the cause of the disease known. Recent studies have indicated that it is a multi-factorial disease with several genes involved. Importantly, sunlight and vitamin D have been implicated in the progression of the disease. The pathogenesis of MS chiefly involves loss of oligodendrocytes, which in addition to being killed by inflammatory mediators in the CNS, also succumbs to loss of trophic support from astrocytes. Neurotrophins play an important role in myelination and the cellular prion protein (PrPC) is a key player in this process. Although the physiological roles of PrPC remain to be fully understood, increasing evidence suggests multiple roles for PrPC in regulation of cellular immunity and for its interaction with several neurotrophins that are necessary for homeostasis of the nervous system. This mini-review focuses on the findings establishing a crucial role for PrPC in the neuropathogenesis of MS, emphasizing its neuroprotective role. Since MS is a multi-factorial disease with unknown etiology and no cure, this review aims to highlight endogenous repair mechanisms mediated by PrPC that might contribute to functional recovery in MS patients.

Peptide reactivity between multiple sclerosis (MS) CSF IgG and recombinant antibodies generated from clonally expanded plasma cells in MS CSF

We employed 19 recombinant antibodies (rAbs) generated from clonally expanded plasma cells, and native IgG from cerebrospinal fluid (CSF) of three multiple sclerosis (MS) patients for panning with phage displayed random peptide libraries. Specific peptide epitopes/mimotopes were identified and characterized. Importantly, peptide-antibody interactions were shared by rAbs and native IgG from the same patient. Three peptides strongly interacted with at least one other MS CSF, but not to inflammatory CNS controls. Database searches revealed several protein candidates including stress proteins, cell surface proteins, and neuronal proteins. Peptides derived from the candidate proteins were recognized by rAbs. Identification of peptide epitopes/mimotopes in MS may provide clues regarding disease-relevant antigens.

A case for regulatory B cells in controlling the severity of autoimmune-mediated inflammation in experimental autoimmune encephalomyelitis and multiple sclerosis

Multiple sclerosis (MS) is considered to be a T cell-mediated autoimmune disease that results in the presence of inflammatory lesions/plaques associated with mononuclear cell infiltrates, demyelination and axonal damage within the central nervous system (CNS). To date, FDA approved therapies in MS are thought to largely function by modulation of the immune response. Since autoimmune responses require many arms of the immune system, the direct cellular mechanisms of action of MS therapeutics are not definitively known. The mouse model of MS, experimental autoimmune encephalomyelitis (EAE), has been instrumental in deciphering the mechanism of action of MS drugs. In addition, EAE has been widely used to study the contribution of individual components of the immune system in CNS autoimmunity. In this regard, the role of B cells in EAE has been studied in mice deficient in B cells due to genetic ablation and following depletion with a B cell-targeted monoclonal antibody (mAb) (anti-CD20). Both strategies have indicated that B cells regulate the extent of EAE clinical disease and in their absence disease is exacerbated. Thus a new population of "regulatory B cells" has emerged. One reoccurring component of regulatory B cell function is the production of IL-10, a pleiotropic cytokine with potent anti-inflammatory properties. B cell depletion has also indicated that B cells, in particular antibody production, play a pathogenic role in EAE. B cell depletion in MS using a mAb to CD20 (rituximab) has shown promising results. In this review, we will discuss the current thinking on the role of B cells in MS drawing from knowledge gained in EAE studies and clinical trials using therapeutics that target B cells.

Somatic hypermutation and antigen-driven selection of B cells are altered in autoimmune diseases

B cells have been found to play a critical role in the pathogenesis of several autoimmune (AI) diseases. A common feature amongst many AI diseases is the formation of ectopic germinal centers (GC) within the afflicted tissue or organ, in which activated B cells expand and undergo somatic hypermutation (SHM) and antigen-driven selection on their immunoglobulin variable region (IgV) genes. However, it is not yet clear whether these processes occurring in ectopic GCs are identical to those in normal GCs. The analysis of IgV mutations has aided in revealing many aspects concerning B cell expansion, mutation and selection in GC reactions. We have applied several mutation analysis methods, based on lineage tree construction, to a large set of data, containing IgV productive and non-productive heavy and light chain sequences from several different tissues, to examine three of the most profoundly studied AI diseases - Rheumatoid Arthritis (RA), Multiple Sclerosis (MS) and Sjögren's Syndrome (SS). We have found that RA and MS sequences exhibited normal mutation spectra and targeting motifs, but a stricter selection compared to normal controls, which was more apparent in RA. SS sequence analysis results deviated from normal controls in both mutation spectra and indications of selection, also showing differences between light and heavy chain IgV and between different tissues. The differences revealed between AI diseases and normal control mutation patterns may result from the different microenvironmental influences to which ectopic GCs are exposed, relative to those in normal secondary lymphoid tissues.

The double-edged sword of autoimmunity: lessons from multiple sclerosis

The relationship between immune responses to self-antigens and autoimmune disease is unclear. In contrast to its animal model experimental autoimmune encephalomyelitis (EAE), which is driven by T cell responses to myelin antigens, the target antigen of the intrathecal immune response in multiple sclerosis (MS) has not been identified. Although the immune response in MS contributes significantly to tissue destruction, the action of immunocompetent cells within the central nervous system (CNS) may also hold therapeutic potential. Thus, treatment of MS patients with glatiramer acetate triggers a protective immune response. Here we review the immunopathogenesis of MS and some recent findings on the mechanism of glatiramer acetate (GA).

The idiotype connection: linking infection and multiple sclerosis

B cells present idiotopes (Id) from their B cell receptor to Id-specific CD4(+) T cells. Chronic Id-driven T-B cell collaboration can cause autoimmune disease in mice. We propose that Id-driven T-B cell collaboration mediates the development of multiple sclerosis by perpetuating immune responses initiated against infectious agents. During germinal centre reactions, B cells express a multitude of mutated Ids. While most mutations lead to decreased affinity and deletion of the B cell, some B cells could be rescued by Id-specific T cells. Such Id-connected T-B cell pairs might initiate inflammatory foci in the central nervous system. This model may explain the intrathecal synthesis of low-avidity IgG against viruses, and the synthesis of oligoclonal IgG with unknown specificity in multiple sclerosis.

Novel approaches for identifying target antigens of autoreactive human B and T cells

Antigen-specific immune responses in multiple sclerosis have been studied for decades, but the target antigens of the putatively autoaggressive B and T cells still remain elusive. Here, we summarize recent strategies which are based on the direct analysis of biopsy or autopsy specimens from patients. Since this material is extremely scarce, the experimental methods need to be exceptionally sensitive. We describe technologies to distinguish (auto) aggressive T cells from irrelevant bystander lymphocytes by analyzing clonal expansions in relation to the morphological location of the cells in the tissue lesions. We then discuss approaches to clone matching α- and β-chains of the antigen-specific T cell receptor (TCR) molecules from single T cells. This is necessary because usually, several clones are expanded and are diluted by many irrelevant cells. The matching TCR chains from individual T cells can be resurrected in hybridoma cells which may then be used for antigen searches. We discuss strategies to identify antigens of γδ- and αβ-TCR molecules, such as biochemical methods, candidate antigens, human leukocyte antigen requirements, synthetic peptide, and cDNA libraries. These strategies are tailored to characterize the antigens of the membrane-anchored, low-affinity TCR molecules. The strategies to identify (auto) reactive B cells or immunoglobulin (Ig) molecules are fundamentally different, because Ig molecules are water-soluble and have high affinities. We further discuss proteome-based approaches, techniques that analyze Ig-chains from single B cells, and a repertoire-based method that compares Ig-proteomes and Ig-transcriptomes. The first method detects Ig antigens directly, whereas the latter two methods allow reconstruction of Ig molecules, which can be used for antigen searches.

Antibodies produced by clonally expanded plasma cells in multiple sclerosis cerebrospinal fluid

OBJECTIVE

Intrathecal IgG synthesis, persistence of bands of oligoclonal IgG, and memory B-cell clonal expansion are well-characterized features of the humoral response in multiple sclerosis (MS). Nevertheless, the target antigen of this response remains enigmatic.

METHODS

We produced 53 different human IgG1 monoclonal recombinant antibodies (rAbs) by coexpressing paired heavy- and light-chain variable region sequences of 51 plasma cell clones and 2 B-lymphocyte clones from MS cerebrospinal fluid in human tissue culture cells. Chimeric control rAbs were generated from anti-myelin hybridomas in which murine variable region sequences were fused to human constant region sequences. Purified rAbs were exhaustively assayed for reactivity against myelin basic protein, proteolipid protein, and myelin oligodendrocyte glycoprotein by immunostaining of transfected cells expressing individual myelin proteins, by protein immunoblotting, and by immunostaining of human brain tissue sections.

RESULTS

Whereas humanized control rAbs derived from anti-myelin hybridomas and anti-myelin monoclonal antibodies readily detected myelin antigens in multiple immunoassays, none of the rAbs derived from MS cerebrospinal fluid displayed immunoreactivity to the three myelin antigens tested. Immunocytochemical analysis of tissue sections from MS and control brain demonstrated only weak staining with a few rAbs against nuclei or cytoplasmic granules in neurons, glia, and inflammatory cells.

INTERPRETATION

The oligoclonal B-cell response in MS cerebrospinal fluid is not targeted to the well-characterized myelin antigens myelin basic protein, proteolipid protein, or myelin oligodendrocyte glycoprotein.

Potential of a unique antibody gene signature to predict conversion to clinically definite multiple sclerosis

We identified a unique antibody gene mutation pattern (i.e. "signature") in cerebrospinal fluid (CSF) B cells from multiple sclerosis (MS) patients not present in control populations. Prevalence of the signature in CSF B cells of patients at risk to develop MS predicted conversion to MS with 91% accuracy in a small cohort of clinically isolated syndrome patients. If confirmed, signature prevalence would be a novel genetic diagnostic tool candidate for patients with early demyelinating disease of the central nervous system.

Multiple sclerosis: clinical features, pathophysiology, neuroimaging and future therapies

Multiple sclerosis (MS) is a common immune-mediated progressive neurodegenerative disease of the CNS that typically manifests with periods of disease activity followed by intervals of remission. The etiology of MS remains unknown; however, existing evidence indicates that MS is a ‘whole-brain disease’ that is driven by a potent immune response against CNS antigen(s), particularly myelin peptide antigens. The immunopathogenesis of MS includes both the cell- and humorally-mediated arms of the immune system. Genetic and environmental factors play important roles in the development of MS. Application of various neuroimaging techniques to the world of MS have expanded our knowledge concerning its pathogenesis and assist us in the more accurate diagnosis of MS versus its imitators. Current treatments target acute attacks and aim to reduce future clinical relapses. A summary of the potential future therapies for MS is presented.

B- and T-cell responses in multiple sclerosis: novel approaches offer new insights

In experimental autoimmune encephalomyelitis (EAE), several target antigens of encephalitogenic T- and B-cell responses have been identified. However, in human multiple sclerosis (MS) the target antigens of pathogenic T and B cells have remained conjectural. Here we discuss how recent methodological advances have offered new insights into the nature of B- and T-cell receptor repertoires expressed in MS tissues, and how novel approaches have helped to identify neurofascin as a target of anti-axonal autoantibodies in MS and EAE.

The role of B cells in multiple sclerosis: rationale for B-cell-targeted therapies

Multiple sclerosis is an inflammatory demyelinating disease of the central nervous system with no clear etiology. Until recently, most studies have emphasized the role of T cells in the pathogenesis of multiple sclerosis. Data suggesting that B cells play a role in the pathogenesis of multiple sclerosis have been accumulating for the past five decades, demonstrating that the cerebrospinal fluid and central nervous system tissues of multiple sclerosis patients contain B cells, plasma cells, antibodies, and immunoglobulins. Data suggest that B cells are involved in antigen capture and presentation to T cells, cytokine production, antibody secretion, demyelination, tissue damage, and remyelination in multiple sclerosis. These advances in the understanding of B-cell and antibody roles in the pathophysiology of multiple sclerosis provide a strong rationale for B-cell-targeted therapies.

The natural history of B cells

Multiple sclerosis is a common neurological disorder that represents a significant source of disability. B cells have recently emerged as a novel therapeutic target for multiple sclerosis. The natural development of B cells is characterized by an antigen-independent phase that occurs in the bone marrow and an antigen-dependent phase that takes place in the peripheral lymphoid tissue. The stage of B-cell development can be identified by the presence of specific cell surface markers. Checkpoints are in place to prevent self-reactive B cells from further development and activation. Some self-reactive B cells are able to escape these checkpoints, resulting in a loss of tolerance. B cells may contribute to systemic autoimmunity and the development of autoimmune disease via cytokine production, antigen presentation, and complement activation. In addition, B cells may trigger autoimmune disease via molecular mimicry, which occurs when a single B-cell receptor recognizes both a non-self antigen molecule and a self-molecule. Accumulating data suggest that ectopic proliferation of B cells in the central nervous system may also play a role. Further research is needed to elucidate the pathology of B cells and their role in central nervous system autoimmune diseases, including multiple sclerosis.

CSF IgG heavy-chain bias in patients at the time of a clinically isolated syndrome

Using FACS and single cell reverse transcriptase polymerase chain reaction, we examined the cerebrospinal fluid (CSF) IgG VH repertoires from 10 subjects with a clinically isolated demyelinating syndrome (CIS). B and plasma cell repertoires from individual subjects showed similar VH family germline usage, nearly identical levels of post-germinal center somatic hypermutation, and significant overlap in their clonal populations. Repertoires from 7 of 10 CIS subjects demonstrated a biased usage of VH4 and/or VH2 family gene segments in their plasma or B cell repertoires. V-regionbias, however, was not observed in the corresponding peripheral blood CD19+ B cell repertoires from 2 CIS subjects or in normal healthy adults. Clinically, subjects with VH4 or VH2 CSF IgG repertoire bias rapidly progressed to definite MS, whereas individuals without repertoire bias did not develop MS after a minimum of 2 years of follow-up (p=0.01).

T cells from multiple sclerosis patients recognize multiple epitopes on Self-IgG

The highly diversified variable regions of immunoglobulin (Ig) molecules contain immunogenic determinants denoted idiotopes. We have previously reported that T cells from multiple sclerosis (MS) patients recognize IgG from autologous cerebrospinal fluid (CSF), and mapped a T-cell epitope to an IgG idiotope. To test the ability of CSF IgG molecules to elicit a broad polyclonal T-cell response in MS, we have analysed T-cell responses in the blood and CSF against idiotope peptides spanning complementarity determining region (CDR) 3 and somatic mutations within the variable regions of monoclonal CSF IgG. Consistent with a diversified idiotope-specific T-cell repertoire, CD4(+) T cells from both patients recognized several idiotope peptides presented by HLA-DR molecules. Mutations were critical for T-cell recognition, as T cells specific for a mutated CDR1 peptide did not recognize corresponding germline-encoded peptides. One T-cell clone recognized both an idiotope peptide and the B-cell clone expressing this idiotope, compatible with endogenous processing and presentation of this idiotope by B cells. These results suggest that mutated CSF IgG from MS patients carry several T-cell epitopes, which could mediate intrathecal IgG production and inflammation in MS through idiotope-driven T-B-cell collaboration.

B cells: no longer the nondominant arm of multiple sclerosis

The role B cells and humoral immunity play in multiple sclerosis (MS) is continually evolving. Recent discoveries include advances in lesion classification, identification of B cell clonal expansion in the central nervous system with evidence of antigen targeting, identification of chemokines in MS lesions, and expansion of information on the roles of autoantibodies and complement. Strong indications are accumulating that a greater degree of humoral dysfunction may lead to worsened long-term prognosis in MS. Effects of established MS treatments on B cells and their products have been further defined. Treatments that specifically target B cells are being implemented and hold promise.

Measles virus-specific plasma cells are prominent in subacute sclerosing panencephalitis CSF

OBJECTIVE

To demonstrate the specificity of expanded CD138(+) plasma cell clones recovered from the CSF of a patient with subacute sclerosing panencephalitis (SSPE) for measles virus (MV).

METHODS

IgG variable region sequences of single-antibody-secreting CD138(+) cells sorted from SSPE CSF were amplified by single-cell PCR and analyzed. Human IgG1 recombinant antibodies (rAbs) were produced from four expanded CD138(+) clones and assayed for immunoreactivity against MV proteins.

RESULTS

Clonal expansion was a prominent feature of the SSPE plasma cell repertoire, and each of the four rAbs assayed was specific for either the MV fusion or the MV nucleocapsid protein.

CONCLUSIONS

Expanded plasma cell clones in the CSF of patients with subacute sclerosing panencephalitis produce disease-relevant antibodies. Recombinant antibodies derived from CSF B cells could provide a tool to identify target antigens in idiopathic inflammatory disorders.

Antigen specificity of clonally expanded and receptor edited cerebrospinal fluid B cells from patients with relapsing remitting MS

We re-engineered the immunoglobulin rearrangements from clonally expanded CSF B cells of three Multiple Sclerosis patients as Fab fragments, and used three methods to test for their antigen (Ag) specificity. Nine out of ten Fab fragments were reactive to Myelin Basic Protein (MBP). The one Fab that did not react to MBP was a product of receptor editing. Two of the nine MBP reactive Fabs were also reactive to GFAP and CNPase, indicating that these clones were polyreactive. Targeting the mechanisms that allow these self-reactive B cells to reside in the CSF of MS patients may prove to be a potent immunotherapeutic strategy.

Cerebrospinal fluid B cells from multiple sclerosis patients are subject to normal germinal center selection

Previous findings from our laboratory demonstrated that some clonally expanded cerebrospinal fluid (CSF) B cells from MS patients exhibit diminished mutation targeting patterns in comparison to typical B cells selected in the context of germinal centers (GCs). In order to determine whether the overall CSF B cell repertoires adhered to mutation patterns typical of GC-selected B cells, we analyzed the immunoglobulin repertoires from CSF B cells of 8 MS patients for mutation characteristics typical of GC-derived B cells. Mutation targeting was preserved. Thus, clonal expansion of some CSF B cells may occur independently of GC, but the CSF B cell pool is governed by typical GC selection. Interestingly, the heavy chain CDR3's of CSF B cells from MS patients had a net acidic charge, similar to GC-derived B cells, but a tendency towards longer CDR3's, consistent with autoreactive B cells. How these findings may support current hypotheses regarding the origin of CSF B cells is discussed.

Rituximab in subacute sclerosing panencephalitis

Subacute sclerosing panencephalitis (SSPE) is a progressive, fatal neurological disorder of childhood and early adolescence. It is caused by a persistent measles virus infection of the brain without any available treatment to date. The physiopathology of the disease is largely unknown. Considering the potential role of humoral immunity in the pathogenesis of SSPE, one patient was given compassionate anti-CD20 antibodies. However, disease progression under treatment led to reconsider B cell involvement in this pathology. Nevertheless, we observed that carbamazepine was useful in improving life quality in our patient, and should be considered as a first-line drug. To date, measles vaccination remains the only solution to SSPE.

The B cell response in multiple sclerosis

Multiple sclerosis (MS) plaques and CSF contain increased amounts of intrathecally synthesized IgG, manifest as oligoclonal bands (OCBs) after protein electrophoresis. OCBs are not unique to MS and are also produced in infectious diseases of the CNS, in which the oligoclonal IgG has been shown to be antibody directed against the disease-causing agent. Thus, analysis of antibody specificity may identify the causative agent/antigen in MS. This review discusses recent studies that have analyzed the phenotypes of B cells in MS which infiltrate the CNS and the molecular features of their antigen-binding regions. Together with histologic studies showing the presence of ectopic lymphoid follicles in the meninges of some MS patients, this data supports the notion of a targeted and compartmentalized humoral response in MS.