Immune complexes and the complement factors C4 and C3 in cerebrospinal fluid and serum from patients with chronic progressive multiple sclerosis

Torben Fog - A Danish pioneer in a multi-faceted spectrum of multiple sclerosis research

Torben Fog was committed to multiple sclerosis (MS) research for more than four decades, starting before the defence of his thesis in 1948 and lasting until his death in 1987. His research was multi-facetted, making him one of the great pioneers in the study of essential parts of the pathology, immunology and treatment of MS. He has contributed with meticulous studies of the MS plaques, documenting the perivenous distribution of plaques in the spinal cord. He constructed a scoring system for the disability in MS and used a computer programme to calculate a total neurological deficit. Together with his co-workers, Fog in 1972 was the first to report the association between MS and the human leukocyte antigen system. Fog can be considered as the father of immunomodulatory therapy in MS, treating MS patients with the first transfer factor, and as early as 1980, he was the first to treat MS with intramuscular natural interferon.

Free complement and complement containing extracellular vesicles as potential biomarkers for neuroinflammatory and neurodegenerative disorders

The complement system is implicated in a broad range of neuroinflammatory disorders such as Alzheimer's disease (AD) and multiple sclerosis (MS). Consequently, measuring complement levels in biofluids could serve as a potential biomarker for these diseases. Indeed, complement levels are shown to be altered in patients compared to controls, and some studies reported a correlation between the level of free complement in biofluids and disease progression, severity or the response to therapeutics. Overall, they are not (yet) suitable as a diagnostic tool due to heterogeneity of reported results. Moreover, measurement of free complement proteins has the disadvantage that information on their origin is lost, which might be of value in a multi-parameter approach for disease prediction and stratification. In light of this, extracellular vesicles (EVs) could provide a platform to improve the diagnostic power of complement proteins. EVs are nanosized double membrane particles that are secreted by essentially every cell type and resemble the (status of the) cell of origin. Interestingly, EVs can contain complement proteins, while the cellular origin can still be determined by the presence of EV surface markers. In this review, we summarize the current knowledge and future opportunities on the use of free and EV-associated complement proteins as biomarkers for neuroinflammatory and neurodegenerative disorders.

Aptamer-based screen of Neuropsychiatric Lupus cerebrospinal fluid reveals potential biomarkers that overlap with the choroid plexus transcriptome

OBJECTIVES

As no gold-standard diagnostic test exists for neuropsychiatric systemic lupus erythematosus (NPSLE), we executed a broad screen of NPSLE cerebrospinal fluid (CSF) using an aptamer-based platform.

METHODS

CSF were obtained from NPSLE patients and subjected to proteomic assay using the aptamer-based screen. Potential biomarkers were identified and validated in independent NPSLE cohorts in comparison with other neurological diseases.

RESULTS

40 proteins out of 1129 screened were elevated in NPSLE CSF. By ELISA validation, CSF Angiostatin, α2-Macroglobulin, DAN, Fibronectin, HCC-1, IgM, Lipocalin 2, M-CSF and SERPING1 were significantly elevated in a predominantly Caucasian NPSLE cohort (n=24), compared to patients with other neurological diseases (n=54), with CSF IgM (AUC=0.95) and M-CSF (AUC=0.91) being the most discriminatory. In a second, Hong Kong NPSLE cohort, CSF IgM (AUC=0.78) and Lipocalin-2 (AUC=0.85) were the most discriminatory. Several CSF proteins exhibited high diagnostic specificity for NPSLE in both cohorts. Elevated CSF C3 was associated with acute confusional state. Eleven molecules elevated in NPSLE CSF exhibited concordant elevation in the choroid plexus, suggesting shared origins.

CONCLUSIONS

CSF Lipocalin-2, M-CSF, IgM and complement C3 emerge as promising CSF biomarkers of NPSLE with diagnostic potential.

Assessing the values of circulating immune complexes in multiple sclerosis patients following immunomodulator or corticosteroid treatment

Multiple sclerosis is defined as an immune-mediated disease that affects the central nervous system, and also is characterized by the presence of immune cells and mediators which contribute to the subsidiary neuroinflammation associated with multiple sclerosis. Throughout the evolution of multiple sclerosis, it has been observed that circulating immune complexes (CICs) have higher values in these patients, especially in the acute phase of the disease. Thus, the aim of the present study was to observe, if in acute attack, relapsing-remitting multiple sclerosis patients still present high values of CICs after treatment with glatiramer and prednisone. We divided 70 patients with multiple sclerosis with high values of CICs into two treatment groups, one treated with glatiramer (Copaxone) (immunomodulatory treatment) and the other with prednisone (corticosteroid treatment). After three months of treatment, we assessed the levels of CICs of the two multiple sclerosis groups and we observed that the patients that followed the immunomodulatory treatment had lower values of CICs than the group that followed the corticosteroid treatment. In addition, another observation established was that the glatiramer treatment group had higher levels of vitamin D in the serum than the prednisone group of multiple sclerosis patients. To conclude, better outcomes, from the point of view of the results obtained from the comparative analysis of the values of CICs and vitamin D, were demonstrated by following immunomodulatory treatment.

An "Outside-In" and "Inside-Out" Consideration of Complement in the Multiple Sclerosis Brain: Lessons From Development and Neurodegenerative Diseases

The last 15 years have seen an explosion of new findings on the role of complement, a major arm of the immune system, in the central nervous system (CNS) compartment including contributions to cell migration, elimination of synapse during development, aberrant synapse pruning in neurologic disorders, damage to nerve cells in autoimmune diseases, and traumatic injury. Activation of the complement system in multiple sclerosis (MS) is typically thought to occur as part of a primary (auto)immune response from the periphery (the outside) against CNS antigens (the inside). However, evidence of local complement production from CNS-resident cells, intracellular complement functions, and the more recently discovered role of early complement components in shaping synaptic circuits in the absence of inflammation opens up the possibility that complement-related sequelae may start and finish within the brain itself. In this review, the complement system will be introduced, followed by evidence that implicates complement in shaping the developing, adult, and normal aging CNS as well as its contribution to pathology in neurodegenerative conditions. Discussion of data supporting "outside-in" vs. "inside-out" roles of complement in MS will be presented, concluded by thoughts on potential approaches to therapies targeting specific elements of the complement system.

Brain-Immune Interactions and Neuroinflammation After Traumatic Brain Injury

Traumatic brain injury (TBI) is the principal cause of death and disability in children and young adults. Clinical and preclinical research efforts have been carried out to understand the acute, life-threatening pathophysiological events happening after TBI. In the past few years, however, it was recognized that TBI causes significant morbidity weeks, months, or years after the initial injury, thereby contributing substantially to the overall burden of TBI and the decrease of life expectancy in these patients. Long-lasting sequels of TBI include cognitive decline/dementia, sensory-motor dysfunction, and psychiatric disorders, and most important for patients is the need for socio-economic rehabilitation affecting their quality of life. Cerebrovascular alterations have been described during the first week after TBI for direct consequence development of neuroinflammatory process in relation to brain edema. Within the brain-immune interactions, the complement system, which is a family of blood and cell surface proteins, participates in the pathophysiology process. In fact, the complement system is part of the primary defense and clearance component of innate and adaptive immune response. In this review, the complement activation after TBI will be described in relation to the activation of the microglia and astrocytes as well as the blood-brain barrier dysfunction during the first week after the injury. Considering the neuroinflammatory activity as a causal element of neurological handicaps, some major parallel lines of complement activity in multiple sclerosis and Alzheimer pathologies with regard to cognitive impairment will be discussed for chronic TBI. A better understanding of the role of complement activation could facilitate the development of new therapeutic approaches for TBI.

Proteomic approach to profiling immune complex antigens in cerebrospinal fluid samples from patients with central nervous system autoimmune diseases

BACKGROUND

Immune complexes (ICs) may clearly reflect immunological abnormalities caused by disease, especially for autoimmune diseases. Although ICs have been detected in cerebrospinal fluid (CSF) from patients with CNS autoimmune diseases, identities of antigens in such ICs have not been comprehensively determined.

METHODS

We used immune complexome analysis, in which nano-liquid chromatography-tandem mass spectrometry is employed to comprehensively identify antigens incorporated into ICs in biological fluids, to characterize ICs in CSF samples from patients with CNS autoimmune diseases, and to find disease-specific IC antigen to a certain CNS autoimmune disease. Also, we compared the IC antigens we identified with the reported CSF proteome or with the published plasma proteome to examine if the method is distinguished from the conventional CSF proteome analysis.

RESULTS

We identified 176 antigens in 78 CSF samples. We then assessed the overlaps among these antigens, the CSF proteome, and the plasma proteome; 140 of the 176 antigens were found to be exclusively detected by our method. Notably, IC-associated suprabasin in CSF was 100% specific to neuropsychiatric systemic lupus erythematosus (NPSLE).

CONCLUSIONS

This report is the first to comprehensively identify the antigens incorporated into ICs in CSF. There was limited overlap between the antigens we identified and the CSF proteome or the plasma proteome; therefore, our method can be distinguished from the conventional CSF proteome analysis. Although the sensitivity of disease-specific IC-antigens detected in immune complexome analysis screening, the sensitivity may be improved by developing an ELISA method specifically for detecting the ICs. Immune complexome analysis of CSF may be a new and promising path to biomarker discovery for diagnosis and study for CNS autoimmune diseases.

Adipsin Is Associated with Multiple Sclerosis: A Follow-Up Study of Adipokines

Background and Objective. The role of adipokines in regulation of immune responses has been recognized, but very little is known about their impact on multiple sclerosis (MS). In this study, we analysed whether the major adipokines are differentially expressed in plasma of patients with different MS subtypes and clinically isolated syndrome (CIS) and explored their association with major disease characteristics. Methods. The levels of adiponectin, adipsin, leptin, and resistin in the plasma of 80 patients with different subtypes of MS and CIS were followed up annually over the two years. The data obtained were correlated with disease activity, EDSS and volumes of T1-weighted lesions (T1-LV), and fluid attenuation inversion recovery lesions (FLAIR-LV) on MRI. Results. In MS group, a correlation was found between the level of adipsin and EDSS score at baseline (r = 0.506, p < 0.001). In RRMS, the levels of adipsin correlated with EDSS scores (r = 0.542, p = 0.002), T1-LV (r = 0.410, p = 0.034), and FLAIR-LV (r = 0.601, p = 0.0001) at baseline and an increase in the T1-LV over the follow-up (r = 0.582, p = 0.003). Associations with other adipokines were not detected. Conclusion. Our exploratory study provides novel insights on the impact of adipokines in MS and suggests that adipsin exerts predictive potential as a biomarker of neurodegeneration.

Enhanced complement consumption in neuromyelitis optica and Behçet's disease patients

The complement system is essential in the pathogenesis of inflammatory central nervous system disorders. To investigate the involvement of complement pathways in neuromyelitis optica (NMO), levels of breakdown products for classical (C4d), alternative (FBb) and common (sC5b-9) pathways were measured in the sera of 28 NMO and control patients (30 Behçet's disease (BD), 29 multiple sclerosis (MS)) and 31 healthy controls by ELISA. Classical and/or alternative pathway consumption was enhanced in NMO and BD patients as compared to MS patients and healthy controls. Our results suggest that NBD and NMO differ from MS by the predominance of complement system involvement.

Complement in multiple sclerosis: its role in disease and potential as a biomarker

Multiple sclerosis (MS) is a common inflammatory disease of the central nervous system with a poorly defined and complex immunopathogenesis. Although initiated by reactive T cells, persistent inflammation is evident throughout the disease course. A contribution from complement has long been suspected, based on the results of pathological and functional studies which have demonstrated complement activation products in MS brain and biological fluids. However, the extent and nature of complement activation and its contribution to disease phenotype and long-term outcome remain unclear. Furthermore, functional polymorphisms in components and regulators of the complement system which cause dysregulation, and are known to contribute to other autoimmune inflammatory disorders, have not been investigated to date in MS in any detail. In this paper we review evidence from pathological, animal model and human functional and genetic studies, implicating activation of complement in MS. We also evaluate the potential of complement components and regulators and their polymorphic variants as biomarkers of disease, and suggest appropriate directions for future research.

Glial cells as targets for cytotoxic immune mediators

Oligodendrocytes and Schwann cells are the glia principally responsible for the synthesis and maintenance of myelin. Damage may occur to these cells in a number of conditions, but perhaps the most studied are the idiopathic inflammatory demyelinating diseases, multiple sclerosis in the CNS, and Guillain-Barré syndrome and its variants in the peripheral nervous system (PNS). This article explores the effects on these cells of cytotoxic immunological and inflammatory mediators: similarities are revealed, of which perhaps the most important is the sensitivity of both Schwann cells and oligodendrocytes to many such agents. This area of research is, however, characterised and complicated by numerous and often very substantial inter-observer discrepancies. Marked variability in cell culture techniques, and in assays of cell damage and death, provide artifactual explanations for some of this variability; true inter-species differences also contribute. Not the least important conclusion centres on the limited capacity of in vitro studies to reveal disease mechanisms: cell culture findings merely illustrate possibilities which must then be tested ex vivo using human tissue samples affected by the relevant disease.

Mechanisms of damage to myelin and oligodendrocytes and their relevance to disease

Oligodendrocytes synthesize and maintain myelin in the central nervous system (CNS). Damage may occur to these cells in a number of conditions, including infections, exposure to toxins, injury, degeneration, or autoimmune disease, arising both in the course of human disease and in experimental animal models of demyelination and dysmyelination; multiple sclerosis is the commonest human demyelinating disorder. Conventional classical accounts of the pathology of this and other myelin diseases have given great insights into their core features, but there remain considerable uncertainties concerning the timing, means and cause(s) of oligodendrocyte and myelin damage. At present, therapeutic efforts largely concentrate on immune manipulation and damage limitation, an approach that has produced only modest effects in multiple sclerosis. One reason for this must be the limited understanding of the mechanisms underlying cell damage - clearly, successful therapeutic strategies for preserving the oligodendrocyte-myelin unit must depend on knowledge of how oligodendrocyte damage and death occurs. In this review, mechanisms of oligodendrocyte and myelin damage are considered, and attempts made to relate them to disease processes, clinical and experimental. The hallmarks of different cell death processes are described, and oligodendrocyte-myelin injury by cellular and soluble mediators is discussed, both in vitro and invivo. Recent developments concerning the pathological involvement of oligodendrocytes in neurodegenerative disease are summarized. Finally, these neuropathological and applied neurobiological observations are drawn together in the context of multiple sclerosis.

Multiple sclerosis: immune mechanism and update on current therapies

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

Cerebrospinal fluid concentrations of the complement MAC inhibitor CD59 in multiple sclerosis and patients with other neurological disorders

Rodent oligodendrocytes have a unique susceptibility among glia to the lytic effects of complement, due in part to a deficiency in CD59 (protectin), a key surface inhibitor of the complement membrane attack complex (MAC). The possibility that shedding of CD59 by human oligodendrocytes contributes to complement-mediated oligodendrocyte injury in inflammatory demyelinating disease has been investigated by estimating levels of CD59 in cerebrospinal fluid samples from 12 patients with demyelinating disease of the central nervous system and 13 with other neurological diseases. No significant differences were found between patients and controls, or between patients with active and those with clinically inactive demyelinating disease, providing no direct support for oligodendrocyte shedding of CD59 in multiple sclerosis.

The pathogenesis of demyelinating disease: insights from cell biology

Cellular and humoral immune mechanisms have been implicated in the pathogenesis of human and experimental demyelinating diseases of the CNS. How these interact in the complex sequence of events that culminates in phagocytosis of myelin by macrophages has yet to be resolved. The relationship between leakage of the blood-brain barrier and demyelination, the reason why recurrent inflammatory demyelination occurs--seemingly in the absence of an antigen-specific immune response--and the lack of effective remyelination all require explanation if a coherent account of immunologically mediated demyelination is to be achieved. One approach to these problems is to study in vitro the developmental and cellular biology of oligodendrocytes--the glial cells responsible for the synthesis and maintenance of CNS myelin. This provides experimental opportunities not offered by more direct investigation of the intact nervous system, but carries the clear disadvantage that observations made in vitro cannot necessarily be extrapolated to humans.

Immune mechanisms in the pathogenesis of demyelinating diseases

The loss of myelin which characterises many human and experimental demyelinating diseases, among them multiple sclerosis, is thought to be immune mediated, but the precise mechanisms responsible remain unknown despite intense research. Normally, myelin in the central nervous system (CNS) is protected from systemic immune responses by the blood brain barrier, which separates nervous tissue from the peripheral circulation. Here we review evidence suggesting that an understanding of the demyelinating disorders may be helped by considering their immune pathogenesis in two stages. The first is damage to the blood brain barrier; this appears to be cell mediated, and allows infiltration into the CNS of other immune effectors. These include complement and also macrophages, which together may mediate the second stage, injury to the myelin/oligodendrocyte complex.

Relevance of platelet factor four (PF4) plasma levels in multiple sclerosis

In order to study the role of platelets in Multiple Sclerosis (MS) we assessed, in a group of patients during a quiescent phase of the disease, the plasma levels of beta-thromboglobulin (beta-TG) and platelet factor four (PF4) both in absence of treatment and during administration of aspirin (ASA) at the dose of 50 mg/daily. In the MS patients studied, the basal plasma levels of beta-TG and PF4 were significantly higher than in control subjects. The increase in the beta-TG plasma levels occurred independently of the age, sex and severity of the disease, whereas the modification in the PF4 plasma levels was significantly correlated with the severity of the disease. Administration to the patients of ASA, at the dose that does not affect prostacyclin production, determined a decrease of beta-TG in 77% of the patients. Mean PF4 plasma levels remained unchanged. These results suggest that PF4 in the plasma of MS patients may originate not only from the platelets but also from the mast cells following platelet aggregating factor (PAF) stimulation and immunocomplex formation.

Detection and isolation of immune complexes in multiple sclerosis cerebrospinal fluid

Immune complexes were studied in the cerebrospinal fluid (CSF) of 20 multiple sclerosis (MS) and 20 other neurological disease (OND) patients using polyethylene glycol precipitation; ten samples from each group were also examined using gel chromatography followed by ELISA. Polyethylene glycol detected predominantly IgG and IgM complexes in 13 of 20 MS samples and four of 20 OND samples. Intact MS complexes ranged in size from 230 to 340 kDa and contained 64 and 53 kDa antigens. Gel chromatography detected IgA complexes in eight of ten MS samples and one of ten OND samples; these complexes appeared to consist of polymeric IgA rather than true antigen. Chromatography detected IgG complexes in nine of ten MS and four of ten OND samples. Intact MS complexes ranged from 240 to 320 kDa and contained 200 and 150 kDa antigens. This study suggests that immune complexes are a very frequent finding in the CSF of MS patients and are in sufficient quantity to visualize on gel electrophoresis.

Intrathecal complement activation in neurological diseases evaluated by analysis of the terminal complement complex

The terminal complement complex (TCC) was determined in plasma and cerebrospinal fluid (CSF) from 208 neurological patients. Elevated CSF TCC levels were observed in higher frequencies in patients with infectious diseases (80%), radiculoneuritis (62%), multiple sclerosis (30%), and miscellaneous autoimmune diseases (27%) than in patients with miscellaneous non-inflammatory diseases (2-13%). The plasma level of TCC was significantly increased only in the infectious group. No positive correlation was observed between the plasma and the CSF TCC concentration in the whole patient population nor in subgroups divided according to blood-brain barrier function. Furthermore, the CSF TCC concentration did not correlate with the serum/CSF albumin ratio or with CSF total protein concentration when this was below 1.0 g/l. It is concluded that an elevated TCC concentration in CSF reflects intrathecal complement activation and that quantification of TCC in CSF may be a valuable supplement in the examination of neurological diseases.

Immunomodulatory factors in cerebrospinal fluid of patients with multiple sclerosis and controls

The immunomodulatory effects of cerebrospinal fluid (CSF) from patients with multiple sclerosis (MS) and other neurologic diseases (OND) were determined by measuring their abilities to suppress alloantigen-specific and nonspecific (IL-2 mediated) proliferative responses. An alloantigen primed, IL-2-dependent line of human T-cells (PLT) was used as indicator. CSF from both patient groups significantly suppressed alloantigen-specific and nonspecific PLT proliferative response. However, patterns of suppression differed between the two groups. While alloantigen-specific proliferative responses were suppressed similarly by MS and controls, CSF from MS patients had significantly less suppressing effect on nonspecific lymphocyte proliferation than did control CSF. The degree of suppression of alloantigen-stimulated proliferation by MS CSF correlated with the concentrations of gamma-globulin and myelin basic protein as well as with the Ig index. Suppression of alloantigen-stimulated proliferation by control CSF correlated only with the concentration of alpha 1-globulin. Sera from 3 MS patients and 7 OND patients were also tested in our system. Only MS sera significantly suppressed the alloantigen stimulated proliferative responses of the PLT. Neither serum group affected nonspecific (IL-2 mediated) proliferation. Our data suggest that there are immunomodulatory factors present in both MS and control CSF, but MS CSF may be relatively lacking in a factor controlling nonspecific lymphocyte proliferation. Deficiency of this factor(s) may contribute to the increased numbers of activated lymphocytes in MS CSF.

Complement in the pathophysiology and diagnosis of human diseases

Complement is a humoral effector system composed of 21 plasma proteins that was identified initially because of its cytolytic effects. In addition to cytolysis, complement has a number of different functions related to inflammatory and other host defense processes. The description of the reaction mechanism includes: (1) activation of the classical pathway through recognition of IgG and IgM antibodies by C1q, (2) activation of the alternative pathway which is usually achieved without participation of immunoglobulins, (3) generation of proteolytic enzymes composed of heteropolymers that cleave certain precursor proteins, (4) formation of the membrane attack complex (MAC), and (5) participation of control mechanisms. Methodologies for studying protein concentration and functional activities of complement components include not only the classical hemolytic techniques but also the extremely sensitive new radioimmunoassays and enzyme immunoassays for measuring the products of complement activation that are generated in vivo. Examples of genetically controlled complement deficiencies have been published for most complement components. The symptomatology of some of these patients serves to emphasize the protective role of complement. Acquired deficiencies are significant not only as laboratory aids in diagnosis and to evaluate the course of certain diseases, but also to indicate possible pathogenic disease mechanisms. Recently, it has been recognized that the complement proteins with genes located in the HLA region are polymorphic. Certain variants of proteins C2, C4, and factor B occur with higher frequencies in certain diseases than in the general population, which appears to be of great practical importance in laboratory medicine.