Ectopic Lymphoid Follicles in Multiple Sclerosis: Centers for Disease Control?

The immunological understanding on germinal center B cells in psoriasis

The development of psoriasis is mainly driven by the dysregulation of T cells within the skin, marking a primary involvement of these cells in the pathogenesis. Although B cells are integral components of the immune system, their role in the initiation and progression of psoriasis is not as pivotal as that of T cells. The paradox of B cell suggests that, while it is crucial for adaptive immunity, B cells may contribute to the exacerbation of psoriasis. Numerous ideas proposed that there are potential relationships between psoriasis and B cells especially within germinal centers (GCs). Recent research projected that B cells might be triggered by autoantigens which then induced molecular mimicry to alter B cells activity within GC and generate autoantibodies and pro-inflammatory cytokines, form ectopic GC, and dysregulate the proliferation of keratinocytes. Hence, in this review, we gathered potential evidence indicating the participation of B cells in psoriasis within the context of GC, aiming to enhance our comprehension and advance treatment strategies for psoriasis thus inviting many new researchers to investigate this issue.

B cells and the stressed brain: emerging evidence of neuroimmune interactions in the context of psychosocial stress and major depression

The immune system has emerged as a key regulator of central nervous system (CNS) function in health and in disease. Importantly, improved understanding of immune contributions to mood disorders has provided novel opportunities for the treatment of debilitating stress-related mental health conditions such as major depressive disorder (MDD). Yet, the impact to, and involvement of, B lymphocytes in the response to stress is not well-understood, leaving a fundamental gap in our knowledge underlying the immune theory of depression. Several emerging clinical and preclinical findings highlight pronounced consequences for B cells in stress and MDD and may indicate key roles for B cells in modulating mood. This review will describe the clinical and foundational observations implicating B cell-psychological stress interactions, discuss potential mechanisms by which B cells may impact brain function in the context of stress and mood disorders, describe research tools that support the investigation of their neurobiological impacts, and highlight remaining research questions. The goal here is for this discussion to illuminate both the scope and limitations of our current understanding regarding the role of B cells, stress, mood, and depression.

Single-Cell Profiling Indicates a Proinflammatory Role of Meningeal Ectopic Lymphoid Tissue in Experimental Autoimmune Encephalomyelitis

BACKGROUND AND OBJECTIVES

The factors that drive progression in multiple sclerosis (MS) remain obscure. Identification of key properties of meningeal inflammation will contribute to a better understanding of the mechanisms of progression and how to prevent it.

METHODS

Applying single-cell RNA sequencing, we compared gene expression profiles in immune cells from meningeal ectopic lymphoid tissue (mELT) with those from secondary lymphoid organs (SLOs) in spontaneous chronic experimental autoimmune encephalomyelitis (EAE), an animal model of MS.

RESULTS

Generally, mELT contained the same immune cell types as SLOs, suggesting a close relationship. Preponderance of B cells over T cells, an increase in regulatory T cells and granulocytes, and a decrease in naïve CD4+ T cells characterize mELT compared with SLOs. Differential gene expression analysis revealed that immune cells in mELT show a more activated and proinflammatory phenotype compared with their counterparts in SLOs. However, the increase in regulatory T cells and upregulation of immunosuppressive genes in most immune cell types indicate that there are mechanisms in place to counter-regulate the inflammatory events, keeping the immune response emanating from mELT in check.

DISCUSSION

Common features in immune cell composition and gene expression indicate that mELT resembles SLOs and may be regarded as a tertiary lymphoid tissue. Distinct differences in expression profiles suggest that mELT rather than SLOs is a key driver of CNS inflammation in spontaneous EAE. Our data provide a starting point for further exploration of molecules or pathways that could be targeted to disrupt mELT formation.

The pathogenesis of multiple sclerosis: a series of unfortunate events

Multiple sclerosis (MS) is characterized by the chronic inflammatory destruction of myelinated axons in the central nervous system. Several ideas have been put forward to clarify the roles of the peripheral immune system and neurodegenerative events in such destruction. Yet, none of the resulting models appears to be consistent with all the experimental evidence. They also do not answer the question of why MS is exclusively seen in humans, how Epstein-Barr virus contributes to its development but does not immediately trigger it, and why optic neuritis is such a frequent early manifestation in MS. Here we describe a scenario for the development of MS that unifies existing experimental evidence as well as answers the above questions. We propose that all manifestations of MS are caused by a series of unfortunate events that usually unfold over a longer period of time after a primary EBV infection and involve periodic weakening of the blood-brain barrier, antibody-mediated CNS disturbances, accumulation of the oligodendrocyte stress protein αB-crystallin and self-sustaining inflammatory damage.

The Impact of Innate Components on Viral Pathogenesis in the Neurotropic Coronavirus Encephalomyelitis Mouse Model

Recognition of viruses invading the central nervous system (CNS) by pattern recognition receptors (PRRs) is crucial to elicit early innate responses that stem dissemination. These innate responses comprise both type I interferon (IFN-I)-mediated defenses as well as signals recruiting leukocytes to control the infection. Focusing on insights from the neurotropic mouse CoV model, this review discusses how early IFN-I, fibroblast, and myeloid signals can influence protective anti-viral adaptive responses. Emphasis is placed on three main areas: the importance of coordinating the distinct capacities of resident CNS cells to induce and respond to IFN-I, the effects of select IFN-stimulated genes (ISGs) on host immune responses versus viral control, and the contribution of fibroblast activation and myeloid cells in aiding the access of T cells to the parenchyma. By unraveling how the dysregulation of early innate components influences adaptive immunity and viral control, this review illustrates the combined effort of resident CNS cells to achieve viral control.

Continued dysregulation of the B cell lineage promotes multiple sclerosis activity despite disease modifying therapies

A clear understanding of the origin and role of the different subtypes of the B cell lineage involved in the activity or remission of multiple sclerosis (MS) is important for the treatment and follow-up of patients living with this disease. B cells, however, are dynamic and can play an anti-inflammatory or pro-inflammatory role, depending on their milieu. Depletion of B cells has been effective in controlling the progression of MS, but it can have adverse side effects. A better understanding of the role of the B cell subtypes, through the use of surface biomarkers of cellular activity with special attention to the function of memory and other regulatory B cells (Bregs), will be necessary in order to offer specific treatments without inducing undesirable effects.

A Dual Role of Osteopontin in Modifying B Cell Responses

The occurrence of B cell aggregates within the central nervous system (CNS) has prompted the investigation of the potential sources of pathogenic B cell and T cell responses in a subgroup of secondary progressive multiple sclerosis (MS) patients. Nevertheless, the expression profile of molecules associated with these aggregates and their role in aggregate development and persistence is poorly described. Here, we focused on the expression pattern of osteopontin (OPN), which is a well-described cytokine, in MS brain tissue. Autopsied brain sections from MS cases with and without B cell pathology were screened for the presence of CD20⁺ B cell aggregates and co-expression of OPN. To demonstrate the effect of OPN on B cells, flow cytometry, ELISA and in vitro aggregation assays were conducted using the peripheral blood of healthy volunteers. Although OPN was expressed in MS brain tissue independent of B cell pathology, it was also highly expressed within B cell aggregates. In vitro studies demonstrated that OPN downregulated the co-stimulatory molecules CD80 and CD86 on B cells. OPN-treated B cells produced significantly lower amounts of IL-6. However, OPN-treated B cells also exhibited a higher tendency to form homotypic cell aggregates in vitro. Taken together, our data indicate a conflicting role of OPN in modulating B cell responses.

Remyelination in animal models of multiple sclerosis: finding the elusive grail of regeneration

Remyelination biology and the therapeutic potential of restoring myelin sheaths to prevent neurodegeneration and disability in multiple sclerosis (MS) has made considerable gains over the past decade with many regeneration strategies undergoing tested in MS clinical trials. Animal models used to investigate oligodendroglial responses and regeneration of myelin vary considerably in the mechanism of demyelination, involvement of inflammatory cells, neurodegeneration and capacity for remyelination. The investigation of remyelination in the context of aging and an inflammatory environment are of considerable interest for the potential translation to progressive multiple sclerosis. Here we review how remyelination is assessed in mouse models of demyelination, differences and advantages of these models, therapeutic strategies that have emerged and current pro-remyelination clinical trials.

B cells going viral in the CNS: Dynamics, complexities, and functions of B cells responding to viral encephalitis

A diverse number of DNA and RNA viruses have the potential to invade the central nervous system (CNS), causing inflammation and injury to cells that have a limited capacity for repair and regeneration. While rare, viral encephalitis in humans is often fatal and survivors commonly suffer from permanent neurological sequelae including seizures. Established treatment options are extremely limited, predominantly relying on vaccines, antivirals, or supportive care. Many viral CNS infections are characterized by the presence of antiviral antibodies in the cerebral spinal fluid (CSF), indicating local maintenance of protective antibody secreting cells. However, the mechanisms maintaining these humoral responses are poorly characterized. Furthermore, while both viral and autoimmune encephalitis are associated with the recruitment of diverse B cell subsets to the CNS, their protective and pathogenic roles aside from antibody production are just beginning to be understood. This review will focus on the relevance of B cell responses to viral CNS infections, with an emphasis on the importance of intrathecal immunity and the potential contribution to autoimmunity. Specifically, it will summarize the newest data characterizing B cell activation, differentiation, migration, and localization in clinical samples as well as experimental models of acute and persistent viral encephalitis.

The CXCL13/CXCR5 Immune Axis in Health and Disease—Implications for Intrathecal B Cell Activities in Neuroinflammation

The chemokine C-X-C- ligand 13 (CXCL13) is a major B cell chemoattractant to B cell follicles in secondary lymphoid organs (SLO) that proposedly recruits B cells to the cerebrospinal fluid (CSF) during neuroinflammation. CXCR5, the cognate receptor of CXCL13, is expressed on B cells and certain T cell subsets, in particular T follicular helper cells (Tfh cells), enabling them to follow CXCL13 gradients towards B cell follicles for spatial proximity, a prerequisite for productive T cell–B cell interaction. Tfh cells are essential contributors to B cell proliferation, differentiation, and high-affinity antibody synthesis and are required for germinal center formation and maintenance. Circulating Tfh cells (cTfh) have been observed in the peripheral blood and CSF. Furthermore, CXCL13/CXCR5-associated immune activities organize and shape adaptive B cell-related immune responses outside of SLO via the formation of ectopic lymphoid structures in inflamed tissues, including the central nervous system (CNS). This review summarizes the recent advances in our understanding of the CXCL13/CXCR5 immune axis and its role in vaccination, autoimmunity, and infection with a special focus on its relevance for intrathecal B cell activities in inflammatory CNS diseases.

Serotonergic drug repurposing in multiple sclerosis: A new possibility for disease-modifying therapy

Investigation of neuroimmune interactions is one of the most developing areas in the study of multiple sclerosis pathogenesis. Recent evidence suggests the possibility of modulating neuroinflammation by targeting biogenic amine receptors. It has been shown that selective serotonin reuptake inhibitor fluoxetine modulates innate and adaptive immune system cells' function and can reduce experimental autoimmune encephalomyelitis and multiple sclerosis severity. This brief report discusses the immune mechanisms underlying the multiple sclerosis pathogenesis and the influence of fluoxetine on them. The retrospective data on the impact of fluoxetine treatment on the course of multiple sclerosis are also presented. The results of this and other studies suggest that fluoxetine could be considered an additional therapy to the standard first-line disease-modifying treatment for relapsing–remitting multiple sclerosis.

Role of Chitinase 3-like 1 as a Biomarker in Multiple Sclerosis: A Systematic Review and Meta-analysis

BACKGROUND AND OBJECTIVES

Multiple sclerosis (MS) is an autoimmune disease confined in the CNS, and its course is frequently subtle and variable. Therefore, predictive biomarkers are needed. In this scenario, we conducted a systematic review and meta-analysis to evaluate the reliability of chitinase 3-like 1 as a biomarker of MS.

METHODS

Research through the main scientific databases (PubMed, Scopus, Web of Science, and Cochrane Library) published from January 2010 to December 2020 was performed using the following keywords: "chitinase 3-like 1 and multiple sclerosis" and "YKL40 and multiple sclerosis." Articles were selected according to the 2020 updated Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines by 2 authors independently, and data were extracted; 20 of the 90 studies screened were included in the meta-analysis. The main efficacy measure was represented by the standardized mean difference of CSF and blood CHI3L1 levels; Review Manager version 5.4 and R software applications were used for analysis.

RESULTS

Higher levels of CHI3L1 were found in CSF of 673 patients with MS compared with 336 healthy controls (size-weighted mean difference [SMD] 50.88; 95% CI = 44.98-56.79; p < 0.00001) and in 461 patients with MS than 283 patients with clinically isolated syndrome (CIS) (SMD 28.18; 95% CI = 23.59-32.76; p < 0.00001). Mean CSF CHI3L1 levels were significantly higher in 561 converting than 445 nonconverting CIS (SMD 30.6; 95% CI = 28.31-32.93; p < 0.00001). CSF CHI3L1 levels were significantly higher in patients with primary progressive MS (PPMS) than in patients with relapsing-remitting MS (RRMS) (SMD 43.15; 95% CI = 24.41-61.90; p < 0.00001) and in patients with secondary progressive MS (SMD 41.86 with 95% CI = 32.39-51.33; p < 0.00001). CSF CHI3L1 levels in 407 patients with MS during remission phase of disease were significantly higher than those in 395 patients with MS with acute relapse (SMD 10.48; 95% CI = 08.51-12.44; p < 0.00001). The performances of CHI3L1 in blood for differentiating patients with MS from healthy controls were not significant (SMD 0.48; 95% CI = -1.18 to 2.14; p: 0.57).

DISCUSSION

CSF levels of CHI3L1 have a strong correlation with the MS pathologic course, in particular with the mechanism of progression of the disease; it helps to distinguish the PPMS from the RRMS. The potential role of CHI3L1 in serum needs to be further studied in the future.

Innate Lymphoid Cells - Neglected Players in Multiple Sclerosis

Multiple sclerosis (MS) is a highly debilitating autoimmune disease affecting millions of individuals worldwide. Although classically viewed as T-cell mediated disease, the role of innate lymphoid cells (ILC) such as natural killer (NK) cells and ILC 1-3s has become a focal point as several findings implicate them in the disease pathology. The role of ILCs in MS is still not completely understood as controversial findings have been reported assigning them either a protective or disease-accelerating role. Recent findings in experimental autoimmune encephalomyelitis (EAE) suggest that ILCs infiltrate the central nervous system (CNS), mediate inflammation, and have a disease exacerbating role by influencing the recruitment of autoreactive T-cells. Elucidating the detailed role of ILCs and altered signaling pathways in MS is essential for a more complete picture of the disease pathology and novel therapeutic targets. We here review the current knowledge about ILCs in the development and progression of MS and preclinical models of MS and discuss their potential for therapeutic applications.

The Neuroimmunology of Multiple Sclerosis: Fictions and Facts

There have been tremendous advances in the neuroimmunology of multiple sclerosis over the past five decades, which have led to improved diagnosis and therapy in the clinic. However, further advances must take into account an understanding of some of the complex issues in the field, particularly an appreciation of “facts” and “fiction.” Not surprisingly given the incredible complexity of both the nervous and immune systems, our understanding of the basic biology of the disease is very incomplete. This lack of understanding has led to many controversies in the field. This review identifies some of these controversies and facts/fictions with relation to the basic neuroimmunology of the disease (cells and molecules), and important clinical issues. Fortunately, the field is in a healthy transition from excessive reliance on animal models to a broader understanding of the disease in humans, which will likely lead to many improved treatments especially of the neurodegeneration in multiple sclerosis (MS).

Role and Relevance of Cerebrospinal Fluid Cells in Diagnostics and Research: State-of-the-Art and Underutilized Opportunities

Cerebrospinal fluid (CSF) has recently experienced a revival in diagnostics and research. However, little progress has been made regarding CSF cell analysis. For almost a century, CSF cell count and cytomorphological examination have been central diagnostic parameters, with CSF pleocytosis as a hallmark finding of neuroinflammation and cytology offering valuable clues regarding infectious, autoimmune, and malignant aetiologies. A great deal of information, however, remains unattended as modern immune phenotyping technologies have not yet been broadly incorporated into routine CSF analysis. This is a serious deficit considering the central role of CSF cells as effectors in central nervous system (CNS) immune defence and autoimmune CNS processes, and the diagnostic challenges posed by clinically overlapping infectious and immune-mediated CNS diseases. Here, we summarize historical, specimen-intrinsic, methodological, and technical issues determining the state-of-the-art diagnostics of CSF cells and outline future perspectives for this underutilized window into meningeal and CNS immunity.

Serum, but Not Saliva, CXCL13 Levels Associate With Infiltrating CXCL13+ Cells in the Minor Salivary Gland Lesions and Other Histologic Parameters in Patients With Sjögren's Syndrome

Recent studies suggest that elevated CXCL13 serum levels in patients with primary Sjögren’s syndrome (pSS) associate with minor salivary gland (MSG) histologic features, disease severity, as well as high-risk status for non-Hodgkin lymphoma (NHL) development and NHL itself. In contrast, limited discriminative value of CXCL13 saliva levels has been reported. Prompt by these reports, we sought to validate the clinical utility of CXCL13 by investigating potential correlations of serum and saliva levels with MSG histopathologic [including CXCL13+-cell number, severity of infiltrates and germinal center (GC) formation], serologic and clinical parameters, as well as NHL. CXCL13 levels were evaluated in paired serum and saliva specimens of 45 pSS patients (15 with NHL; pSS-associated NHL: SSL), 11 sicca-controls (sicca-complaining individuals with negative MSG biopsy and negative autoantibody profile), 10 healthy individuals (healthy-controls) and 6 non-SS-NHLs. CXCL13+-cells were measured in paired MSG-tissues of 22 of pSS patients studied (including 7 SSLs) and all sicca-controls. CXCL13 serum levels were significantly increased in pSS and SSL patients compared to sicca- and healthy-controls and were positively correlated with the CXCL13+-cell number and biopsy focus-score. Serum CXCL13 was significantly higher in pSS patients with GCs, rheumatoid factor, hypocomplementemia, high disease activity, NHL and in high-risk patients for NHL development. CXCL13 saliva levels were significantly increased in SSL patients (compared to non-SS-NHLs), patients with GCs and in high-risk for NHL patients. Univariate analysis revealed that CXCL13 serum, but not saliva, levels were associated with lymphoma, an association that did not survive multivariate analysis. Conclusively, our findings confirm that serum, but not saliva, levels of CXCL13 are associated with histologic, serologic and clinical features indicative of more severe pSS.

The CXCL13/CXCR5-chemokine axis in neuroinflammation: evidence of CXCR5+CD4 T cell recruitment to CSF

Background

C-X-C chemokine ligand 13 (CXCL13) is frequently elevated in cerebrospinal fluid (CSF) in a variety of inflammatory central nervous system (CNS) diseases, has been detected in meningeal B cell aggregates in brain tissues of multiple sclerosis patients, and proposedly recruits B cells into the inflamed CNS. Besides B cells also follicular helper T (Tfh) cells express the cognate receptor C-X-C chemokine receptor type 5 (CXCR5) and follow CXCL13 gradients in lymphoid tissues. These highly specialized B cell helper T cells are indispensable for B cell responses to infection and vaccination and involved in autoimmune diseases. Phenotypically and functionally related circulating CXCR5+CD4 T cells occur in blood. Their co-recruitment to the inflamed CSF is feasible but unresolved.

Methods

We approached this question with a retrospective study including data of all patients between 2017 and 2019 of whom immune phenotyping data of CXCR5 expression and CSF CXCL13 concentrations were available. Discharge diagnoses and CSF laboratory parameters were retrieved from records. Patients were categorized as pyogenic/aseptic meningoencephalitis (ME, n = 29), neuroimmunological diseases (NIMM, n = 22), and non-inflammatory neurological diseases (NIND, n = 6). ANOVA models and Spearman’s Rank-Order correlation were used for group comparisons and associations of CXCL13 levels with immune phenotyping data.

Results

In fact, intrathecal CXCL13 elevations strongly correlated with CXCR5+CD4 T cell frequencies in the total cohort (p < 0.0001, r = 0.59), and ME (p = 0.003, r = 0.54) and NIMM (p = 0.043, r = 0.44) patients. Moreover, the ratio of CSF-to-peripheral blood (CSF/PB) frequencies of CXCR5+CD4 T cells strongly correlated with CXCL13 levels both in the total cohort (p = 0.001, r = 0.45) and ME subgroup (p = 0.005, r = 0.50), indicating selective accumulation. ME, NIMM and NIND groups differed with regard to CSF cell counts, albumin quotient, intrathecal IgG, CXCL13 elevations and CXCR5+CD4 T cells, which were higher in inflammatory subgroups.

Conclusion

The observed link between intrathecal CXCL13 elevations and CXCR5+CD4 T cell frequencies does not prove but suggests recruitment of possible professional B cell helpers to the inflamed CSF. This highlights CSF CXCR5+CD4 T cells a key target and potential missing link to the poorly understood phenomenon of intrathecal B cell and antibody responses with relevance for infection control, chronic inflammation and CNS autoimmunity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-021-00272-1.

A Milestone in Multiple Sclerosis Therapy: Monoclonal Antibodies Against CD20-Yet Progress Continues

Multiple sclerosis (MS), which is a chronic inflammatory disease of the central nervous system, still represents one of the most common causes of persisting disability with an early disease onset. Growing evidence suggests B cells to play a crucial role in its pathogenesis and progression. Over the last decades, monoclonal antibodies (mabs) against the surface protein CD20 have been intensively studied as a B cell targeting therapy in relapsing MS (RMS) as well as primary progressive MS (PPMS). Pivotal studies on anti-CD20 therapy in RMS showed remarkable clinical and radiological effects, especially on acute inflammation and relapse biology. These results paved the way for further research on the implication of B cells in the pathogenesis of MS. Besides controlling relapse development in RMS, ocrelizumab (OCR) also showed clinical benefits in patients with PPMS and became the first approved drug for this disease course. In this review, we provide an overview of the current anti-CD20 mabs used or tested for the treatment of MS-namely rituximab (RTX), OCR, ofatumumab (OFA), and ublituximab (UB). Besides their effectiveness, we also discuss possible limitations and safety concerns especially in regard to long-term treatment, both for this class of drugs overall as well as for each anti-CD20 mab individually. Additionally, we elucidate to what extent anti-CD20 therapy may alter the function of other immune cells, both directly or indirectly. Finally, we cover the current knowledge on repopulation of CD20+ cells after cessation of anti-CD20 treatment and discuss future aspirations towards alternative, further developed B cell silencing therapies.