B-lymphocyte and plasma cell clonal expansion in monosymptomatic optic neuritis cerebrospinal fluid

Pathogenic myelin-specific antibodies in multiple sclerosis target conformational proteolipid protein 1-anchored membrane domains

B cell clonal expansion and cerebrospinal fluid (CSF) oligoclonal IgG bands are established features of the immune response in multiple sclerosis (MS). Clone-specific recombinant monoclonal IgG1 Abs (rAbs) derived from MS patient CSF plasmablasts bound to conformational proteolipid protein 1 (PLP1) membrane complexes and, when injected into mouse brain with human complement, recapitulated histologic features of MS pathology: oligodendrocyte cell loss, complement deposition, and CD68+ phagocyte infiltration. Conformational PLP1 membrane epitopes were complex and governed by the local cholesterol and glycolipid microenvironment. Abs against conformational PLP1 membrane complexes targeted multiple surface epitopes, were enriched within the CSF compartment, and were detected in most MS patients, but not in inflammatory and noninflammatory neurologic controls. CSF PLP1 complex Abs provide a pathogenic autoantibody biomarker specific for MS.

Coronaviruses and their relationship with multiple sclerosis: is the prevalence of multiple sclerosis going to increase after the Covid-19 pandemia?

The purpose of this review is to examine whether there is a possible (etiological/triggering) relationship between infection with various Coronaviruses, including Severe Acute Respiratory Syndrome-related Coronavirus-2 (SARS-CoV-2), the virus responsible for the Coronavirus disease-19 (Covid-19) pandemia, and Multiple Sclerosis (MS), and whether an increase of the prevalence of MS after the current Covid-19 pandemia should be expected, examining new and preexisting data. Although the exact pathogenesis of MS remains unknown, environmental agents seem to greatly influence the onset of the disease, with viruses being the most popular candidate. Existing data support this possible etiological relationship between viruses and MS, and experimental studies show that Coronaviruses can actually induce an MS-like demyelinating disease in animal models. Findings in MS patients could also be compatible with this coronaviral MS hypothesis. More importantly, current data from the Covid-19 pandemia show that SARS-CoV-2 can trigger autoimmunity and possibly induce autoimmune diseases, in the Central Nervous System as well, strengthening the viral hypothesis of MS. If we accept that Coronaviruses can induce MS, it is reasonable to expect an increase in the prevalence of MS after the Covid-19 pandemia. This knowledge is of great importance in order to protect the aging groups that are more vulnerable against autoimmune diseases and MS specifically, and to establish proper vaccination and health policies.

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.

A Neuroprimer: Principles of Central Nervous System Immunity

Despite longstanding perceptions, robust innate and adaptive immune responses occur within the central nervous system (CNS) in response to infection and tissue damage. Although necessary to control infection, immune responses can lead to severe CNS pathology in the context of both viral infection and autoimmunity. Research into how the central nervous and immune systems communicate has accelerated over the past 20 years leading to a better understanding of pathways controlling immune activation and neuroinflammation that have guided the approval of new disease-modifying therapies to treat CNS immunopathology, particularly the inflammatory demyelinating disease multiple sclerosis. This article provides an introduction into the basic principles underlying immune responses within the CNS that developed from experimental animal models of both neurotropic virus infection and autoimmune T cell-mediated CNS demyelination.

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.

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.

ATON: results from a Phase II randomized trial of the B-cell-targeting agent atacicept in patients with optic neuritis

The 36-week ATON study compared the efficacy and safety of atacicept with matching placebo in 34 patients with unilateral optic neuritis as a clinically isolated syndrome. Atacicept (150mg) was administered twice weekly for 4weeks (loading period), then once weekly for 32weeks. The ATON study was terminated prematurely by the sponsor when an independent Data and Safety Monitoring Board review observed increased multiple sclerosis (MS)-related disease activity in the atacicept arms of the concurrent ATAcicept in MS (ATAMS) study. Analysis of the prematurely terminated ATON study showed that the mean (standard deviation) change from baseline in retinal nerve fiber layer thickness at last observed value in the affected eye was -8.6 (10.1) μm in patients treated with atacicept (n=15) compared with -17.3 (15.2) μm in patients treated with placebo (n=16). In the atacicept treatment group, a higher proportion of patients converted to clinically definite MS during the double-blind period compared with placebo (35.3% [6/17] vs 17.6% [3/17]). Treatment-emergent adverse events were similar across both treatment groups in the double-blind period. A dichotomy emerged with more atacicept-treated patients converting to relapsing-remitting MS compared with placebo-treated patients, despite the same patients experiencing less axonal loss after an optic neuritis event.

Viruses and multiple sclerosis

Multiple sclerosis (MS) is a chronic demyelinating disorder of unknown etiology, possibly caused by a virus or virus-triggered immunopathology. The virus might reactivate after years of latency and lyse oligodendrocytes, as in progressive multifocal leukoencephalopathy, or initiate immunopathological demyelination, as in animals infected with Theiler's murine encephalomyelitis virus or coronaviruses. The argument for a viral cause of MS is supported by epidemiological analyses and studies of MS in identical twins, indicating that disease is acquired. However, the most important evidence is the presence of bands of oligoclonal IgG (OCBs) in MS brain and CSF that persist throughout the lifetime of the patient. OCBs are found almost exclusively in infectious CNS disorders, and antigenic targets of OCBs represent the agent that causes disease. Here, the authors review past attempts to identify an infectious agent in MS brain cells and discuss the promise of using recombinant antibodies generated from clonally expanded plasma cells in brain and CSF to identify disease-relevant antigens. They show how this strategy has been used successfully to analyze antigen specificity in subacute sclerosing panencephalitis, a chronic encephalitis caused by measles virus, and in neuromyelitis optica, a chronic autoimmune demyelinating disease produced by antibodies directed against the aquaporin-4 water channel.

Viruses and Multiple Sclerosis

Multiple sclerosis (MS) is a chronic demyelinating disorder of unknown etiology, possibly caused by a virus or virus-triggered immunopathology. The virus might reactivate after years of latency and lyse oligodendrocytes, as in progressive multifocal leukoencephalopathy, or initiate immunopathological demyelination, as in animals infected with Theiler’s murine encephalomyelitis virus or coronaviruses. The argument for a viral cause of MS is supported by epidemiological analyses and studies of MS in identical twins, indicating that disease is acquired. However, the most important evidence is the presence of bands of oligoclonal IgG (OCBs) in MS brain and CSF that persist throughout the lifetime of the patient. OCBs are found almost exclusively in infectious CNS disorders, and antigenic targets of OCBs represent the agent that causes disease. Here, the authors review past attempts to identify an infectious agent in MS brain cells and discuss the promise of using recombinant antibodies generated from clonally expanded plasma cells in brain and CSF to identify disease-relevant antigens. They show how this strategy has been used successfully to analyze antigen specificity in subacute sclerosing panencephalitis, a chronic encephalitis caused by measles virus, and in neuromyelitis optica, a chronic autoimmune demyelinating disease produced by antibodies directed against the aquaporin-4 water channel.

Inhibition of glyceraldehyde-3-phosphate dehydrogenase activity by antibodies present in the cerebrospinal fluid of patients with multiple sclerosis

We have previously shown that B cells and Abs reactive with GAPDH and antitriosephosphate isomerase (TPI) are present in lesions and cerebrospinal fluid (CSF) in multiple sclerosis (MS). In the current study, we studied the effect of anti-GAPDH and anti-TPI CSF IgG on the glycolytic enzyme activity of GAPDH and TPI after exposure to intrathecal IgG from 10 patients with MS and 34 patients with other neurologic diseases. The degree of inhibition of GAPDH activity by CSF anti-GAPDH IgG in the seven MS samples tested varied from 13 to 98%, which seemed to correlate with the percentage of anti-GAPDH IgG in the CSF IgG (1-45%). Inhibition of GAPDH activity (18 and 23%) by CSF IgG was seen in two of the 34 patients with other neurologic diseases, corresponding to the low percentage of CSF anti-GAPDH IgG (1 and 8%). In addition, depletion of anti-GAPDH IgG from CSF IgG, using immobilized GAPDH, removed the inhibitory effect of the IgG on GAPDH. No inhibition of GAPDH activity was seen with CSF samples not containing anti-GAPDH IgG. No inhibition of TPI activity was seen with any purified CSF IgG sample. These findings demonstrate an increased percentage of anti-GAPDH Abs in the CSF of patients with MS that can inhibit GAPDH glycolytic enzyme activity and may contribute to neuroaxonal degeneration.

Intrathecal pathogenic anti-aquaporin-4 antibodies in early neuromyelitis optica

OBJECTIVE

The serum of most neuromyelitis optica (NMO) patients contains autoantibodies (NMO-IgGs) directed against the aquaporin-4 (AQP4) water channel located on astrocyte foot processes in the perivessel and subpial areas of the brain. Our objectives were to determine the source of central nervous system (CNS) NMO-IgGs and their role in disease pathogenesis.

METHODS

Fluorescence-activated cell sorting and single-cell reverse transcriptase polymerase chain reaction were used to identify overrepresented plasma cell immunoglobulin (Ig) sequences in the cerebrospinal fluid (CSF) of an NMO patient after a first clinical attack. Monoclonal recombinant antibodies (rAbs) were generated from the paired heavy and light chain sequences and tested for target specificity and Fc effector function. The effect of CSF rAbs on CNS immunopathology was investigated by delivering single rAbs to rats with experimental autoimmune encephalomyelitis (EAE).

RESULTS

Repertoire analysis revealed a dynamic, clonally expanded plasma cell population with features of an antigen-targeted response. Using multiple independent assays, 6 of 11 rAbs generated from CSF plasma cell clones specifically bound to AQP4. AQP4-specific rAbs recognized conformational epitopes and mediated both AQP4-directed antibody-dependent cellular cytotoxicity and complement-mediated lysis. When administered to rats with EAE, an AQP4-specific NMO CSF rAb induced NMO immunopathology: perivascular astrocyte depletion, myelinolysis, and complement and Ig deposition.

INTERPRETATION

Molecular characterization of the CSF plasma cell repertoire in an early NMO patient demonstrates that AQP4-specific Ig is synthesized intrathecally at disease onset and directly contributes to CNS pathology. AQP4 is now the first confirmed antigenic target in human demyelinating disease.

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).

Analysis of cerebrospinal fluid cell populations with monoclonal antibodies

Sixty-five samples of cerebrospinal fluid (CSF) were evaluated using an automated cytoflow method with the CD-Sapphire hematology analyzer in order to investigate possible relationships between cell population patterns and diagnostic groups and better understand the biology of neurological disease. A basic panel of CD markers, including CD3/4/8/19/138/HLA-DR, was used to analyze CSF samples from clinical and laboratory confirmed cases of multiple sclerosis, neuroborreliosis, viral and bacterial neuroinfective diseases, malignant infiltrations of meninges and scavenger macrophagic reactions of the central nervous system. The principles of immune response and the contribution of cytological 'disease-related patterns' for these nosological entities are described. The distinct patterns of lymphocyte subpopulations in neuroborreliosis appear to be characteristic and could possibly serve as diagnostic indicators. Further verification and research will be necessary to clarify the significance and nature of CD4+ CD8+ positive subset in cerebrospinal fluid.

B cells and autoantibodies in the pathogenesis of multiple sclerosis and related inflammatory demyelinating diseases

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system (CNS). The mainstream view is that MS is caused by an autoimmune attack of the CNS myelin by myelin-specific CD4 T cells, and this perspective is supported by extensive work in the experimental autoimmune encephalomyelitis (EAE) model of MS as well as immunological and genetic studies in humans. However, it is important to keep in mind that other cell populations of the immune system are also essential in the complex series of events leading to MS, as exemplified by the profound clinical efficacy of B cell depletion with Rituximab. This review discusses the mechanisms by which B cells contribute to the pathogenesis of MS and dissects their role as antigen-presenting cells (APCs) to T cells with matching antigen specificity, the production of proinflammatory cytokines and chemokines, as well as the secretion of autoantibodies that target structures on the myelin sheath and the axon. Mechanistic dissection of the interplay between T cells and B cells in MS may permit the development of B cell based therapies that do not require depletion of this important cell population.

Germinal center B-cell-associated DNA hypomethylation at transcriptional regions of the AID gene

T-cell-dependent antigen induces differentiation of germinal center (GC) B-cell in peripheral lymphoid follicles. We studied whether GC B-cell differentiation is associated with DNA methylation status by examining regulatory regions of mouse AID transcription that are essential for B-cell maturation. AID-negative cell lines of pre-B cells, immature B cells, mature B cells, plasmacytomas or T cells showed various hypermethylation profiles in the 5'-promoter and intronic regions. In contrast, AID-positive GC-type B cells were hypomethylated in these regions. Stimulation of splenic B cells with lipopolysaccharide and interleukin-4 caused DNA hypomethylation in the 5'-promoter and intronic CpG sites proportional to the increase in AID transcription. Mature GL7+Fas+ GC B cells were hypomethylated at these CpG sites, especially near the Pax5-consensus site and an intronic site. However, Syndecan-1+ plasma cells showed DNA hypermethylation, as seen in plasmacytomas. Methylation status of the transcriptional regulatory region might contribute to stage-dependent activation of AID transcription during GC B-cell differentiation.

New directions in optic neuritis and multiple sclerosis

Optic neuritis (ON) is the initial presentation in 15% to 20% of cases of multiple sclerosis (MS). Thirty-eight percent to 50% of patients with MS develop ON at some point during the course of their disease. The Optic Neuritis Treatment Trial (ONTT) provided much prospective data about the clinical presentation, clinical course with respect to treatment, and development of MS in patients with ON. The clinical course of MS initially involves episodes of demyelination followed by full recovery; however, later attacks often leave persistent deficits that lead to secondary progression of the disease. The risk of developing progressive neurologic deficits can be reduced by starting therapy with immunomodulating drugs early in the course of the disease. Optical coherence tomography is a noninvasive way to monitor patients with ON to determine if they are undergoing subclinical axonal loss of ganglion cells. Progression of axonal loss on optical coherence tomography may prompt a change in therapy or further imaging.

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.

Triosephosphate isomerase- and glyceraldehyde-3-phosphate dehydrogenase-reactive autoantibodies in the cerebrospinal fluid of patients with multiple sclerosis

Our previous results revealed that Igs in lesions and single chain variable fragment Abs (scFv-Abs) generated from clonal B cells in the cerebrospinal fluid (CSF) from patients with multiple sclerosis (MS) bind to axons in MS brains. To study the axonal Ags involved in MS, we identified the glycolytic enzymes, triosephosphate isomerase (TPI) and GAPDH, using Igs from the CSF and scFv-Abs generated from clonal B cells in the CSF and in lesions from MS patients. Elevated levels of CSF-Abs to TPI were observed in patients with MS (46%), clinically isolated syndrome (CIS) suggestive of MS (40%), other inflammatory neurological diseases (OIND; 29%), and other noninflammatory neurological diseases (ONIND; 31%). Levels of GAPDH-reactive Abs were elevated in MS patients (60%), in patients with CIS (10%), OIND (14%), and ONIND (8%). The coexistence of both autoantibodies was detected in 10 MS patients (29%), and 1 CIS patient (3%), but not in patients with OIND/ONIND. Two scFv-Abs generated from the CSF and from lesions of a MS brain showed immunoreactivity to TPI and GAPDH, respectively. The findings suggest that TPI and GAPDH may be candidate Ags for an autoimmune response to neurons and axons in MS.

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.

Optic neuritis and the neuro-ophthalmology of multiple sclerosis

Multiple sclerosis (MS) is the most common cause of neurological disability in young adults. Since approximately 40% of the brain is devoted to vision, demyelination commonly affects visual function, resulting in a myriad of neuro-ophthalmic symptoms. In this chapter, we examine the seminal afferent and efferent neuro-ophthalmological manifestations of MS, highlighting those history and examination findings critical for the diagnosis and treatment of various visual and ocular motor disorders. Among the topics, a special emphasis will be placed on optic neuritis, the most common clinically isolated demyelinating syndrome. This chapter focuses on the evaluation and treatment of visual sensory and oculomotor disorders in MS. The objective is to provide the reader with a working model for enhancing their care of patients with demyelinating disease.

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.

B lineage cells in the inflammatory central nervous system environment: Migration, maintenance, local antibody production, and therapeutic modulation

B cells have long played an enigmatic role in the scenario of multiple sclerosis pathogenesis. This review summarizes recent progress in our understanding of B-cell trafficking, survival, and differentiation in the central nervous system (CNS). We propose four possible routes of intrathecal immunoglobulin-producing cells. The inflammatory CNS provides a unique, B-cell-friendly environment, in which B lineage cells, notably long-lived plasma cells, can survive for many years, perhaps even for a lifetime. These new findings offer a plausible explanation for the notorious persistence and stability of cerebrospinal fluid oligoclonal bands. Furthermore, we highlight similarities and differences of intrathecal immunoglobulin production in multiple sclerosis patients and patients with other CNS inflammatory conditions. Finally, we outline the possibly double-edged effects of B cells and immunoglobulin in the CNS and discuss various therapeutic strategies for targeting the B-cell response.

Restrictive and diversifying elements of the anti-myelin/oligodendrocyte glycoprotein antibody response in primate experimental allergic encephalomyelitis

Autoantibody responses against conformational epitopes of myelin/oligodendrocyte glycoprotein (MOG) possess myelin destructive potential, as demonstrated in the marmoset model of human multiple sclerosis (MS) and in some rodent models of experimental allergic encephalomyelitis. We have previously characterized monoclonal Fab fragments specific for conformational epitopes of MOG that were derived from a combinatorial antibody library generated from a MOG-immune marmoset. In this paper, we address the molecular heterogeneity of humoral responses against MOG in this outbred model of MS by studying additional antibody clones derived from a genetically unrelated animal. We find that all MOG-specific IgGkappa Fab fragments, unrelated to genetic make-up, utilize a restricted set of variable region genes, IGHV1 and IGHV3 for the H chain and IGKV1, IGKV3, and IGKV5 for the L chain. Despite these restricting factors, diversity within these antibody repertoires can be observed, predominantly within the H-chain CDR3 regions. Our findings suggest that only a limited set of Ig genes is necessary to launch a diverse, destructive humoral immune response against a single CNS antigen in primates. These results are the first to contribute to a better understanding of how myelin-directed and potentially destructive autoantibody responses may develop in human MS.

Chemokines in multiple sclerosis: CXCL12 and CXCL13 up-regulation is differentially linked to CNS immune cell recruitment

Understanding the mechanisms of immune cell migration to multiple sclerosis lesions offers significant therapeutic potential. This study focused on the chemokines CXCL12 (SDF-1) and CXCL13 (BCA-1), both of which regulate B cell migration in lymphoid tissues. We report that immunohistologically CXCL12 was constitutively expressed in CNS parenchyma on blood vessel walls. In both active and chronic inactive multiple sclerosis lesions CXCL12 protein was elevated and detected on astrocytes and blood vessels. Quantitative PCR demonstrated that CXCL13 was produced in actively demyelinating multiple sclerosis lesions, but not in chronic inactive lesions or in the CNS of subjects who had no neurological disease. CXCL13 protein was localized in perivascular infiltrates and scattered infiltrating cells in lesion parenchyma. In the CSF of relapsing-remitting multiple sclerosis patients, both CXCL12 and CXCL13 were elevated. CXCL13, but not CXCL12, levels correlated strongly with intrathecal immunoglobulin production as well as the presence of B cells, plasma blasts and T cells. About 20% of CSF CD4+ cells and almost all B cells expressed the CXCL13 receptor CXCR5. In vitro, CXCL13 was produced by monocytes and at much higher levels by macrophages. CXCL13 mRNA and protein expression was induced by TNFalpha and IL-1beta but inhibited by IL-4 and IFNgamma. Together, CXCL12 and CXCL13 are elevated in active multiple sclerosis lesions and CXCL12 also in inactive lesions. The consequences of CXCL12 up-regulation could be manifold. CXCL12 localization on blood vessels indicates a possible role in leucocyte extravasation, and CXCL12 may contribute to plasma cell persistence since its receptor CXCR4 is retained during plasma cell differentiation. CXCL12 may contribute to axonal damage as it can become a neurotoxic mediator of cleavage by metalloproteases, which are present in multiple sclerosis lesions. The strong linkage of CXCL13 to immune cells and immunoglobulin levels in CSF suggests that this is one of the factors that attract and maintain B and T cells in inflamed CNS lesions. Therefore, both CXCL13 and CXCR5 may be promising therapeutic targets in multiple sclerosis.

Pathogenesis of multiple sclerosis

PURPOSE OF REVIEW

The aim of this article is to describe recent observations regarding the basis for the initiation and disease evolution of multiple sclerosis.

RECENT FINDINGS

A current debate is where and what initiates the neuroinflammatory reaction that characterizes the acute multiple sclerosis lesion. Immune sensitization to neural antigens could develop within the systemic compartment consequent to exposure to cross-reacting, possibly viral derived, peptides (molecular mimicry). Although CD4 T cells are considered central to initiating central nervous system inflammation, the actual extent and specificity of tissue injury reflects the array of adaptive (CD8 T cells and antibody) and innate (microglia/macrophages) immune constituents present in the lesions. Neuropathologic studies indicate that lethal changes in neural cells (oligodendrocytes) could also be the initiating event, reflecting as yet unidentified acquired insults (e.g. exogenous virus or reactivated endogenous retrovirus) or intrinsic abnormalities ('neurodegenerative' hypothesis). Recurrence or persistence of the disease process can reflect events occurring at multiple sites including expansion of the immune repertoire in response to neural antigens transported to regional lymph nodes (determinant spreading), especially if immune regulatory mechanisms are defective; alterations in blood-brain barrier properties consequent to initial cellular transmigration; and participation of endogenous (microglia, astrocytes) or long lived infiltrating cells (macrophages, B cells in ectopic germinal centers) in regulating and effecting immune functions within the central nervous system. Accumulating neurologic deficit reflects the balance between injury and repair; the latter also being negatively or positively (trophic support and clearance of tissue debris) impacted by inflammatory processes.

SUMMARY

Understanding the full spectrum of multiple sclerosis presents a continuing challenge for both immunology and neurobiology.

Infectious causes of multiple sclerosis

Multiple sclerosis (MS) is a serious chronic neurological disorder in which demyelination and inflammation occur in the white matter of the CNS. The findings of many epidemiological studies and a discordance of MS in monozygotic twins suggest that the disorder is acquired. The most likely cause is a virus because more than 90% of patients with MS have high concentrations of IgG, manifest as oligoclonal bands, in the brain and CSF. Most chronic inflammatory CNS disorders are infectious. More indirect evidence that MS is caused by a virus is the association of several viruses with demyelinating encephalomyelitis in human beings, and the induction of demyelination in animals infected with viruses in research. Nevertheless, no virus has been isolated from the brains of patients who had MS. Molecular analysis of IgG gene specificity in the brain and CSF of those with MS has shown features of an antigen-driven response: clonal amplification and extensive somatic mutations. A viral antigen against which the IgG in MS brain and CSF is directed might be identified.

Polyclonal B-Cell Expansion in the Cerebrospinal Fluid of Patients with Psedotumor Cerebri

To investigate the hypothesis that pseudotumor cerebri (PTC) is associated with humoral immunity, we analyzed immunoglobulin heavy chain variable region (Ig-VH) genes of B cells in the cerebrospinal fluid (CSF) of 10 patients with PTC. Using RT-PCR and sequencing techniques, intrathecal B-cell Ig-VH genes were amplified in 6 of 10 PTC samples. Sequence analysis of complementarity-determining region 3 (CDR 3) and VH genes revealed a polyclonal intrathecal B-cell expansion in these patients. The nucleotide sequences showed that one-third of analyzed sequences had a high replacement to silent nucleotide substitution ratio, indicating an antigen-driven T-cell-dependent intrathecal B-cell proliferation. Moreover, other one-third had germline VH genes without or with a few nucleotide mutations, suggesting a T-cell-independent natural B-cell-mediated humoral immunity in the CNS of these patients. Our results suggest that both T-cell-dependent and T-cell-independent humoral immunity are present in the CSF of PTC.