Quantitative analysis of monoclonal immunoglobulins in serum of patients with amyotrophic lateral sclerosis

Immunology of amyotrophic lateral sclerosis - role of the innate and adaptive immunity

This review aims to summarize the latest evidence about the role of innate and adaptive immunity in Amyotrophic Lateral Sclerosis (ALS). ALS is a devastating neurodegenerative disease affecting upper and lower motor neurons, which involves essential cells of the immune system that play a basic role in innate or adaptive immunity, that can be neurotoxic or neuroprotective for neurons. However, distinguishing between the sole neurotoxic or neuroprotective function of certain cells such as astrocytes can be challenging due to intricate nature of these cells, the complexity of the microenvironment and the contextual factors. In this review, in regard to innate immunity we focus on the involvement of monocytes/macrophages, microglia, the complement, NK cells, neutrophils, mast cells, and astrocytes, while regarding adaptive immunity, in addition to humoral immunity the most important features and roles of T and B cells are highlighted, specifically different subsets of CD4+ as well as CD8+ T cells. The role of autoantibodies and cytokines is also discussed in distinct sections of this review.

Investigation of the causal relationship between ALS and autoimmune disorders: a Mendelian randomization study

BACKGROUND

Epidemiological studies have reported an association between amyotrophic lateral sclerosis (ALS) and different autoimmune disorders. This study aims to explore the causal relationship between autoimmune disorders and ALS using Mendelian randomization (MR).

METHODS

To test the genetically predicted effects of liability towards immune-related outcomes on ALS risk, we used summary statistics from the largest European genome-wide association studies (GWAS) for these disorders in a two-sample MR setting. To do this, we extracted single nucleotide polymorphisms (SNPs) from the GWAS, which strongly associated with the 12 traits, and queried their effects in a large European ALS GWAS (27,265 cases and 110,881 controls). To avoid bias in our MR instruments related to the complex linkage disequilibrium structure of the human leukocyte antigen (HLA) region, we excluded SNPs within this region from the analyses. We computed inverse-variance weighted (IVW) MR estimates and undertook sensitivity analyses using MR methods robust to horizontal pleiotropy. We also performed a reverse MR analysis testing the causal effects of ALS on the above autoimmune traits.

RESULTS

After applying Bonferroni correction for multiple testing, our MR analyses showed that the liability to autoimmune disorders does not affect ALS risk. Our reverse MR analysis also did not support the effects of liability to ALS on other autoimmune disorders. The results of the main IVW MR analyses were generally supported by our sensitivity MR analyses. The variance in the exposures explained by the sets of SNPs used as MR instruments ranged from 8.1 × 10^-4 to 0.31. Our MR study was well-powered to detect effects as small as an odds ratio (OR) of 1.045 for ALS in the main MR and as small as an OR of 1.32 in the reverse MR.

CONCLUSION

Our MR study does not support a relationship between liability to autoimmune disorders and ALS risk in the European population. The associations observed in epidemiological studies could be partly attributed to shared biology or environmental confounders.

Polygenic associations and causal inferences between serum immunoglobulins and amyotrophic lateral sclerosis

BACKGROUND

Due to the limitations like reverse causation and residual confounding commonly seen in the observational studies, the relationship between serum immunoglobulins and amyotrophic lateral sclerosis (ALS) remains unclear.

METHODS

Summary statistics from large-scale genome-wide association studies (GWAS) among European ancestry populations (~15,000 individuals for serum immunoglobulins, and more than 36,000 individuals for ALS) were accessed and used in the discovery and replication phase, respectively. Polygenic risk score analysis was performed to test the polygenic association, and Mendelian randomization analysis was used to infer the causality.

RESULTS

An inverse polygenic association was discovered between IgA and ALS, as well as between IgM and ALS. Such associations were however not replicated using a larger GWAS of ALS, and no causal association was observed for either IgA-ALS or IgM-ALS. For IgG and ALS, a positive polygenic association was both discovered [odds ratio (OR) = 1.18, 95% confidence interval (CI): 1.12-1.25, P = 5.9x10^-7] and replicated (OR = 1.13, 95% CI: 1.06-1.20, P = 0.001). A causal association between IgG and ALS was suggested in the discovery analysis (OR = 1.06, 95 %CI: 1.02-1.10, P = 0.009), but it was not statistically significant in the replication analysis (OR = 1.07, 95 %CI: 0.90-1.24, P = 0.420).

CONCLUSION

This study suggests a positive polygenic association between serum IgG and ALS.

Inflammation in ALS/FTD pathogenesis

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are neurodegenerative diseases that overlap in their clinical presentation, pathology and genetics, and likely represent a spectrum of one underlying disease. In ALS/FTD patients, neuroinflammation characterized by innate immune responses of tissue-resident glial cells is uniformly present on end-stage pathology, and human imaging studies and rodent models support that neuroinflammation begins early in disease pathogenesis. Additionally, changes in circulating immune cell populations and cytokines are found in ALS/FTD patients, and there is evidence for an autoinflammatory state. However, despite the prominent role of neuro- and systemic inflammation in ALS/FTD, and experimental evidence in rodents that altering microglial function can mitigate pathology, therapeutic approaches to decrease inflammation have thus far failed to alter disease course in humans. Here, we review the characteristics of inflammation in ALS/FTD in both the nervous and peripheral immune systems. We further discuss evidence for direct influence on immune cell function by mutations in ALS/FTD genes including C9orf72, TBK1 and OPTN, and how this could lead to the altered innate immune system “tone” observed in these patients.

Microglia and C9orf72 in neuroinflammation and ALS and frontotemporal dementia

Amyotrophic lateral sclerosis (ALS) is a degenerative disorder that is characterized by loss of motor neurons and shows clinical, pathological, and genetic overlap with frontotemporal dementia (FTD). Activated microglia are a universal feature of ALS/FTD pathology; however, their role in disease pathogenesis remains incompletely understood. The recent discovery that ORF 72 on chromosome 9 (C9orf72), the gene most commonly mutated in ALS/FTD, has an important role in myeloid cells opened the possibility that altered microglial function plays an active role in disease. This Review highlights the contribution of microglia to ALS/FTD pathogenesis, discusses the connection between autoimmunity and ALS/FTD, and explores the possibility that C9orf72 and other ALS/FTD genes may have a "dual effect" on both neuronal and myeloid cell function that could explain a shared propensity for altered systemic immunity and neurodegeneration.

Decreased level of serum autoantibody against LG72 is a biosignature of amyotrophic lateral sclerosis

AIM

LG72 can increase mitochondrial ROSs and oxidative stress has been implicated in the pathophysiology of amyotrophic lateral sclerosis (ALS). The serum level of LG72 or LG72-related molecules might therefore be associated with ALS. Here, we aim to determine the serum autoantibody against LG72 has potential as a biomarker for the diagnosis of ALS.

MATERIALS

Seventy-eighty patients with ALS, 45 patients with AD, 43 patients with PD and 88 healthy adults were enrolled.

RESULTS

The concentration of serum autoantibody against LG72 was more than fourfold lower in ALS than other control groups (p < 0.001). The AUC was 0.9627 when the cut-off value for autoantibody concentration was 0.167 μg/ml.

CONCLUSION

This finding suggests that the autoantibody against LG72 might serve as a surrogate biomarker for ALS.

Novel molecular biomarkers at the blood-brain barrier in ALS

Recently neuroinflammation has gained a particular focus as a key mechanism of ALS. Several studies in vivo as well as in vitro have nominated immunoglobulin G (IgG) isolated from ALS patients as an active contributor to disease onset and progression. We have shown that ALS IgG affects astroglial Ca²⁺ excitability and induces downstream activation of phosphatidylinositol 3-kinase. These studies were hampered by a lack of knowledge of the pathway of entry of immune factors in the CNS. Our MRI data revealed the blood-brain barrier BBB leakage and T cell infiltration into brain parenchyma in ALS G93A rats. Since astrocyte ensheathes blood vessel wall contributing to BBB stability and plays an important role in ALS pathogenesis, we have studied astrocytic membrane proteins water channel aquaporin-4 and the inwardly rectifying potassium channel. In this review, we will summarize data related to BBB disruption with particular emphasis on impaired function of astrocytes in ALS. We will discuss implication of membrane proteins expressed on astrocytic endfeet, aquaporin-4, and inwardly rectifying potassium channel in the pathology of ALS. In addition to ALS-specific IgGs, these membrane proteins are proposed as novel biomarkers of the disease.

Humoral immune activation in amyotrophic lateral sclerosis patients

There is evidence that immunological factors may involved in the pathogenetic mechanisms of amyotrophic lateral sclerosis (ALS). Few studies to date have explored the status of the humoral immune response in patients with ALS. We examined the presence of humoral immune activation in ALS patients, serum immunoglobulins (IgG, IgA and IgM) levels were measured in 36 patients with ALS and 35 normal controls. Serum IgG, IgM and IgA levels were not significantly different in our ALS patients compared with the control group (P=ns). No correlations of serum IgG, IgM and IgA concentrations with duration, severity of the disease or the clinical form of onset (bulbar or spinal) were found in our ALS patients. Our results do not suggest a humoral immune activation in ALS patients. This does not exclude that immunological mechanisms may be involved in ALS pathogenesis.

Amyotrophic lateral sclerosis immunoglobulins G enhance the mobility of Lysotracker-labelled vesicles in cultured rat astrocytes

AIM

We examined the effect of purified immunoglobulins G (IgG) from patients with amyotrophic lateral sclerosis (ALS) on the mobility and exocytotic release from Lysotracker-stained vesicles in cultured rat astrocytes.

METHODS

Time-lapse confocal images were acquired, and vesicle mobility was analysed before and after the application of ALS IgG. The vesicle counts were obtained to assess cargo exocytosis from stained organelles.

RESULTS

At rest, when mobility was monitored for 2 min in bath with Ca(2+), two vesicle populations were discovered: (1) non-mobile vesicles (6.1%) with total track length (TL) < 1 μm, averaging at 0.33 ± 0.01 μm (n = 1305) and (2) mobile vesicles (93.9%) with TL > 1 μm, averaging at 3.03 ± 0.01 μm (n = 20,200). ALS IgG (0.1 mg mL(-1)) from 12 of 13 patients increased the TL of mobile vesicles by approx. 24% and maximal displacement (MD) by approx. 26% within 4 min, while the IgG from control group did not alter the vesicle mobility. The mobility enhancement by ALS IgG was reduced in extracellular solution devoid of Ca(2+), indicating that ALS IgG vesicle mobility enhancement involves changes in Ca(2+) homeostasis. To examine whether enhanced mobility relates to elevated Ca(2+) activity, cells were stimulated by 1 mm ATP, a cytosolic Ca(2+) increasing agent, in the presence (2 mm) and in the absence of extracellular Ca(2+). ATP stimulation triggered an increase in TL by approx. 7% and 12% and a decrease in MD by approx. 11% and 1%, within 4 min respectively. Interestingly, none of the stimuli triggered the release of vesicle cargo.

CONCLUSION

Amyotrophic lateral sclerosis-IgG-enhanced vesicle mobility in astrocytes engages changes in calcium homeostasis.

ALS-IgG-induced selective motor neurone apoptosis in rat mixed primary spinal cord cultures

There is evidence that in sporadic amyotrophic lateral sclerosis (ALS) immunological mechanisms may be involved in the pathophysiology of the disease. We tested whether purified IgG from ALS patients induce cell death in rat mixed primary spinal cord cultures and compared this with the effect of IgG purified from patients with Guillain-Barré syndrome (GBS) or from healthy donors. Treatment with ALS-IgG increases caspase-3 apoptosis when compared with control IgG or with GBS-IgG, but does not induce death by necrosis. Because ALS is characterized by the selective loss of motor neurones, we next assessed the differential effect of ALS-IgG on motor neurones or astrocytes. We showed, semiquantitatively, that motor neurones are more susceptible to apoptosis when cultures were treated with ALS-IgG compared with control-IgG. In conclusion, we have demonstrated in primary spinal cord cultures that IgG from patients with ALS induces apoptosis selectively in motor neurones, and that the caspase-3 pathway is involved. This suggests that immunological mechanisms may contribute to the selective loss of motor neurones in ALS.

Evidence for systemic immune system alterations in sporadic amyotrophic lateral sclerosis (sALS)

Sporadic amyotrophic lateral sclerosis (sALS) is a progressive neuroinflammatory disease of spinal cord motor neurons of unclear etiology. Blood from 38 patients with sALS, 28 aged-match controls, and 25 Alzheimer's disease (AD) patients were evaluated and activated monocyte/macrophages were observed in all patients with sALS and AD; the degree of activation was directly related to the rate of sALS disease progression. Other parameters of T-cell activation and immune globulin levels showed similar disease associated changes. These data are consistent with a disease model previously suggested for AD, wherein systemic immunologic activation plays an active role in sALS.

Amyotrophic lateral sclerosis patient IgG alters voltage dependence of Ca2+ channels in dissociated rat motoneurons

Previous studies on sporadic amyotrophic lateral sclerosis (SALS) have detected IgG within motoneurons of patients and these IgGs have been shown to alter voltage dependent calcium channel activity in various cell types. The current study investigates whether IgG from categorized SALS patients alter voltage dependent calcium currents in rat motoneurons in culture. Patients were categorized based on onset and progression pattern. IgG yields were 38% higher in SALS patients compared to control subjects. Incubation with 1 mg/ml IgG from SALS patients did not cause visible toxicity, alter input resistance, capacitance or the maximal calcium conductance in rat motoneurons when compared to motoneurons incubated with control IgG. However, the activation curve of calcium current was shifted to the left in motoneurons treated with SALS IgG compared to control IgG.

Can antiglycolipid antibodies present in HIV-infected individuals induce immune demyelination?

Of the eight clinically defined neuropathies associated with HIV infection, there is compelling evidence that acute and chronic inflammatory demyelinating polyneuropathy (IDPN) have an autoimmune pathogenesis. Many non-HIV infected individuals who suffer from sensory-motor nerve dysfunction have autoimmune indicators. The immunopathogenesis of demyelination must involve neuritogenic components in myelin. The various antigens suspected to play a role in HIV-seronegative IDPN include (i) P2 protein; (ii) sulfatide (GalS); (iii) various gangliosides (especially GM1); (iv) galactocerebroside (GalC); and (v) glycoproteins or glycolipids with the carbohydrate epitope glucuronyl-3-sulfate. These glycoproteins or glycolipids may be individually targeted, or an immune attack may be raised against a combination of any of these epitopes. The glycolipids, however, especially GalS, have recently evoked much interest as mediators of immune events underlying both non-HIV and HIV-associated demyelinating neuropathies. The present review outlines the recent research findings of antiglycolipid antibodies present in HIV-infected patients with and without peripheral nerve dysfunction, in an attempt to arrive at some consensus as to whether these antibodies may play a role in the immunopathogenesis of HIV-associated inflammatory demyelinating polyneuropathy.

In vitro induction of neuronal apoptosis by anti-Fas antibody-containing sera from amyotrophic lateral sclerosis patients

Sera from 26% of patients with sporadic amyotrophic lateral sclerosis (ALS) induced in vitro apoptosis of a human neuroblastoma cell line, as detected by two methods, and most contained anti-Fas autoantibodies. In contrast, Alzheimer sera (studied as controls) very rarely induced apoptosis and did not contain detectable anti-Fas antibodies. Soluble Fas-ligand levels in ALS sera were not different from those in normal sera, except for slightly higher levels in a single case. In mixed cultures of rat embryonic brain and spinal cord cells, ALS sera (and agonistic anti-Fas monoclonal antibodies and soluble Fas-ligand) induced the apoptosis of a subpopulation of neurons. These neurons were motoneurons on the basis of staining with the monoclonal antibody SMI 32 and Fas expression was restricted to these SMI 32-positive neurons. These data are compatible with the hypothesis of the participation of an autoimmune mechanism possibly related to anti-Fas autoantibodies in certain ALS patients.

Serum autoantibodies to neurofilament proteins in sporadic amyotrophic lateral sclerosis

Anti-neurofilament (NF) autoantibodies were searched for by enzyme-linked immunosorbent assays (ELISA) in the serum from 85 sporadic amyotrophic lateral sclerosis (ALS) patients, 98 healthy controls and 79 patients with unrelated immunological diseases (Guillain-Barré syndrome, myasthenia gravis and multiple sclerosis). ELISA cutoff value was determined as mean control levels +2 SD and it corresponded to a specificity of 94%. Such high level antibodies were detected in 24.7% of ALS patients contrasting with 12.6% of neurological controls (P<0.05) and only 6.1% of healthy subjects (P<5.10[-4]). In ALS, anti-NF antibodies were significantly associated with a slow evolution, as measured by the mean time spent in the initial functional states. They did not relate with age, sex and clinical form. The predominant isotype of the anti-NF antibodies was IgM lambda by ELISA. In contrast to negative sera, indirect immunohistochemical studies demonstrated that most sera positive for anti-NF antibodies reacted with axons with predominant isotypes restricted to IgM lambda. By using Western blotting, small amounts of serum monoclonal IgM were found with a high frequency in anti-NF antibody-positive patients. These results suggest the possible involvement of anti-NF antibodies in an autoimmune process in a subgroup of ALS patients.

Altered muscle calcium channel binding kinetics in autoimmune motoneuron disease

While skeletal muscle is not apparently affected directly in amyotrophic lateral sclerosis (ALS), immunoglobulin G fractions purified from patients with ALS (ALS IgG) bind dihydropyridine (DHP)-sensitive L-type voltage-gated calcium channel (VGCC) antigen isolated from skeletal muscle in ELISA and Western immunoblot, and alter VGCC function in vitro. To determine whether muscle VGCC properties are altered in ALS, VGCC-enriched subsarcolemmal membrane fractions were prepared from biopsied quadriceps muscle of patients with ALS, with other neurologic diseases, or without apparent muscle disease, and tested for DHP binding with [3H]PN200-110. ALS muscle VGCCs possessed eightfold higher binding affinities for [3H]PN200-110 than did VGCCs from muscle fractions of most other patients, independent of denervation-induced increases in DHP binding site number. Similarly elevated DHP binding affinities were observed in specimens from patients with autoimmune motor neuropathies, suggesting that ALS and immune mediated motoneuron disease share skeletal muscle L-type VGCC alterations.

Evidence for autoimmunity in amyotrophic lateral sclerosis

Although the etiology and pathogenesis of ALS is unknown, increasing evidence supports a role for autoimmune mechanisms in motoneuron degeneration and death. An animal model, experimental autoimmune gray matter disease, can be induced by the inoculation of spinal cord gray matter. The experimental disease is characterized by weakness secondary to the loss of upper and lower motoneurons, accompanied by inflammatory foci within the spinal cord, and IgG at the neuromuscular junction and within UMN and LMN. In human ALS, IgG is present within the UMN and LMN, and T-lymphocytes and activated microglia have been identified within spinal cord gray matter and motor cortex. ALS IgG can passively transfer physiological changes of the neuromuscular junction to mice resulting in enhanced release of acetylcholine. The ALS IgG selectively interact with calcium channels and alter channel function. These data suggest a potential role for autoimmune mechanisms in the destruction and loss of motoneurons in ALS.

Amyotrophic lateral sclerosis patient antibodies label Ca2+ channel alpha 1 subunit

Sporadic amyotrophic lateral sclerosis is an idiopathic human degenerative disease of spinal cord and brain motor neurons. Prior studies demonstrated that most patients with amyotrophic lateral sclerosis possess immunoglobulins that bind to purified L-type voltage-gated calcium channels, that titers of anti-voltage-gated calcium channel antibodies correlate with disease progression rates, and that amyotrophic lateral sclerosis patient-derived antibodies (ALS IgG) produce electrophysiological changes in the function of voltage-gated calcium channels. Using Western transfer immunoblots and enzyme-linked immunosorbent assays, the calcium ionophore-forming alpha 1 subunit of the voltage-gated calcium channel is now identified as the major voltage-gated calcium channel antigen to which ALS IgG binds. Additionally, the binding of an L-type voltage-gated calcium channel alpha 1 subunit-directed monoclonal antibody, which itself mimics the effects of ALS IgG on skeletal muscle voltage-gated calcium channel currents, is selectively prevented by preaddition of ALS IgG. Voltage-gated calcium channel-binding IgG from patients with Lambert-Eaton myasthenic syndrome appears to be differentiated from ALS IgG by the reactivity of the former to both alpha 1 and beta subunits of the calcium channel. These assays provide further evidence linking amyotrophic lateral sclerosis to an autoimmune process, and suggest one means to differentiate immunoglobulins from patients with amyotrophic lateral sclerosis from those of patients with another autoimmune disease expressing calcium channel antibodies.

Evidence for autoimmunity in amyotrophic lateral sclerosis

Although the etiology and pathogenesis of ALS is unknown, increasing evidence supports a role for autoimmune mechanisms in motoneuron degeneration and death. An animal model, experimental autoimmune gray matter disease, can be induced by the inoculation of spinal cord gray matter. The experimental disease is characterized by weakness secondary to the loss of upper and lower motoneurons, accompanied by inflammatory foci within the spinal cord, and IgG at the neuromuscular junction and within UMN and LMN. In human ALS, IgG is present within the UMN and LMN, and T-lymphocytes and activated microglia have been identified within spinal cord gray matter and motor cortex. ALS IgG can passively transfer physiological changes of the neuromuscular junction to mice resulting in enhanced release of acetylcholine. The ALS IgG selectively interact with calcium channels and alter channel function. These data suggest a potential role for autoimmune mechanisms in the destruction and loss of motoneurons in ALS.

Antiglycolipid antibodies, immunoglobulins and paraproteins in motor neuron disease: a population based case-control study

The role of humoral autoimmune factors in the pathogenesis of motor neuron disease (MND) is currently under considerable scrutiny. In particular, there have been many reports of abnormal serum immunoglobulin patterns and elevated titres of anti-ganglioside antibodies in patients with MND. However, many of these studies may be biased by the selection criteria for patients and controls. In order to carefully address this issue we obtained 82 blood samples from consecutive MND patients identified through a national MND register in combination with 82 community controls matched for age, sex and geographical area. We used these samples to determine the frequency of monoclonal immunoglobulins (mIgs) and measure the levels of serum immunoglobulins and anti-GM1 ganglioside antibodies in sporadic cases of MND in comparison with normal controls. Serum mIgs detected using high resolution and immunofixation agarose electrophoresis were present in 1.2% of MND patients and 2.4% of controls. Using a highly sensitive isoelectric focusing and immunoblotting method, monoclonal or oligoclonal immunoglobulins were found in 28% of MND patients and 27% of controls. Anti-GM1 antibodies were present in 26% of MND patients and 18% of controls (odds ratio = 1.5, 95%, CI 0.7-3.6) with no significant differences in titres between the 2 groups. Mean immunoglobulin G, A and M levels were equal in 2 groups. Thus, although alterations in these parameters were identified, we were unable to demonstrate any significant difference between MND patients and controls. We conclude that the majority of sporadic cases of MND are unlikely to have an autoimmune basis as judged by the lack of abnormalities in these parameters.