Humoral and cellular immune parameters before and during immunosuppressive therapy of a patient with stiff-man syndrome and insulin dependent diabetes mellitus

Toward curing neurological autoimmune disorders: Biomarkers, immunological mechanisms, and therapeutic targets

Autoimmune neurology is a rapidly expanding field driven by the discovery of neuroglial autoantibodies and encompassing a myriad of conditions affecting every level of the nervous system. Traditionally, autoantibodies targeting intracellular antigens are considered markers of T cell-mediated cytotoxicity, while those targeting extracellular antigens are viewed as pathogenic drivers of disease. However, recent advances highlight complex interactions between these immune mechanisms, suggesting a continuum of immunopathogenesis. The breakdown of immune tolerance, central to these conditions, is affected by modifiable and non-modifiable risk factors such as genetic predisposition, infections, and malignancy. While significant therapeutic advancements have revolutionized treatment of certain diseases, such as neuromyelitis optica, our understanding of many others, particularly T cell-mediated conditions, remains limited, with fewer treatment options available. Future research should focus on improving effector function modeling and deepening our understanding of the factors influencing immune tolerance, with the goal of providing novel treatment options and improving patient care.

Diabetes in stiff-person syndrome

Anti-glutamic acid decarboxylase (GAD) autoantibodies are a hallmark of stiff-person syndrome (SPS) and insulin-dependent diabetes mellitus (IDDM). However, patients with concurrent IDDM and SPS often manifest insulin resistance, and SPS-associated IDDM probably has heterogeneous causes. Some patients manifest IDDM associated only with high titers of anti-GAD65 caused by SPS. By contrast, other patients develop IDDM only after being treated with high-dose corticosteroids or they progress to insulin dependency following their treatment with high-dose corticosteroids. The profile of autoantibodies differs markedly between type 1 diabetes mellitus (T1DM), late-onset diabetes mellitus, and SPS-associated IDDM. Therefore, as with new-onset diabetes after transplantation (NODAT), SPS-associated IDDM should be classified as a specific diabetes entity, the pathophysiology of which requires increased attention.

Expanding Role of T Cells in Human Autoimmune Diseases of the Central Nervous System

It is being increasingly recognized that a dysregulation of the immune system plays a vital role in neurological disorders and shapes the treatment of the disease. Aberrant T cell responses, in particular, are key in driving autoimmunity and have been traditionally associated with multiple sclerosis. Yet, it is evident that there are other neurological diseases in which autoreactive T cells have an active role in pathogenesis. In this review, we report on the recent progress in profiling and assessing the functionality of autoreactive T cells in central nervous system (CNS) autoimmune disorders that are currently postulated to be primarily T cell driven. We also explore the autoreactive T cell response in a recently emerging group of syndromes characterized by autoantibodies against neuronal cell-surface proteins. Common methodology implemented in T cell biology is further considered as it is an important determinant in their detection and characterization. An improved understanding of the contribution of autoreactive T cells expands our knowledge of the autoimmune response in CNS disorders and can offer novel methods of therapeutic intervention.

Stiff-person syndrome (SPS) and anti-GAD-related CNS degenerations: protean additions to the autoimmune central neuropathies

Stiff Person Syndrome (SPS) is a rare autoimmune neurological disease attributable to autoantibodies to glutamic acid decarboxylase (anti-GAD) more usually associated with the islet beta cell destruction of autoimmune type 1 diabetes (T1D). SPS is characterized by interference in neurons with the synthesis/activity of the inhibitory neurotransmitter gamma amino butyric acid (GABA) resulting in the prototypic progressive spasmodic muscular rigidity of SPS, or diverse neurological syndromes, cerebellar ataxia, intractable epilepsy, myoclonus and several others. Remarkably, a single autoantibody, anti-GAD, can be common to widely different disease expressions, i.e. T1D and SPS. One explanation for these data is the differences in epitope engagement between the anti-GAD reactivity in SPS and T1D: in both diseases, anti-GAD antibody reactivity is predominantly to a conformational epitope region in the PLP- and C-terminal domains of the 65 kDa isoform but, additionally in SPS, there is reactivity to conformational epitope(s) on GAD67, and short linear epitopes in the C-terminal region and at the N-terminus of GAD65. Another explanation for disease expressions in SPS includes ready access of anti-GAD to antigen sites due to immune responsiveness within the CNS itself according to intrathecal anti-GAD-specific B cells and autoantibody. Closer study of the mysterious stiff-person syndrome should enhance the understanding of this disease itself, and autoimmunity in general.

The potential of multimer technologies in type 1 diabetes prediction strategies

Type 1 diabetes is an autoimmune disease which occurs in (human leukocyte antigen) genetically predisposed individuals as a consequence of the organ-specific immune destruction of the insulin-producing β cells in the islets of Langherans within the pancreas. Type 1 diabetes is the result of a breakdown in immune regulation that leads to expansion of autoreactive CD4+ and CD8+ T cells, autoantibody-producing B lymphocytes and activation of the innate immune system. Islet-related autoantibodies revealed themselves to be good predictors of future onset of the disease, although they are not directly pathogenetic; T cells instead play a dominant role in disease initiation and progression. In this review, we first discuss the approaches that several laboratories attempted to measure human islet autoantigen-specific T-cell function in type 1 diabetes. T-cell assays could be used in combination with standardized autoantibody screenings to improve predictive strategies. They could also help to monitor in long-term follow-up the efficacy of tolerogenic immunotherapeutic strategies when established at the onset of the disease, and help to predict the recurrence of disease. Although some recent developments based on enzyme-linked immunosorbent spot and immunoblotting techniques have been able to distinguish with good sensitivity and specificity patients from controls, T-cell results, as revealed by international workshops, were indeed largely inconclusive. Nowadays, novel technologies have been exploited that could contribute to answering the tantalizing question of identifying autoreactive T cells. We particularly focus on and discuss MHC multimer tools and emphasize the advantages they can offer but also their weaknesses when used in combination with other T-cell assays. Copyright © 2011 John Wiley & Sons, Ltd.

Characterization of CD4+ T cells specific for glutamic acid decarboxylase (GAD65) and proinsulin in a patient with stiff-person syndrome but without type 1 diabetes

BACKGROUND

Glutamic acid decarboxylase (GAD) is a rate-limiting enzyme in the synthesis of gamma-amino butyric acid (GABA) and an important autoantigen both in patients with type 1 diabetes (T1D) and stiff-person syndrome (SPS). Autoantibodies (GADA) to the 65-kDa isoform of GAD are a characteristic feature in both diseases. Approximately 30% of patients with SPS develop diabetes, yet, it is unclear to which extent co-existing autoimmunity to GAD65 and other islet autoantigens determines the risk of developing T1D.

METHODS

In this study, we monitored CD4+ T-cell responses to GAD65 and proinsulin in a patient with SPS who remained normoglycaemic during the 46-month follow-up.

RESULTS

Fluctuating but persistent T-cell reactivity to GAD65 was identified, as well as T-cell reactivity to proinsulin at one time point. The majority of the T-cell clones isolated from the patient with SPS produced high levels of Th2 cytokines (IL-13, IL-5 and IL-4). We also examined levels of GADA, insulin and IA-2 autoantibodies, and epitope specificity of GADA. In both serum and cerebrospinal fluid (CSF), GADA levels were high, and GADA persisted throughout the follow-up. Despite T-cell reactivity to both GAD65 and proinsulin, autoantibodies to other islet autoantigens did not develop.

CONCLUSIONS

Further follow-up will determine whether the beta-cell autoimmunity observed in this patient will eventually lead to T1D.

Central nervous system destruction mediated by glutamic acid decarboxylase-specific CD4+ T cells

High titers of autoantibodies against glutamic acid decarboxylase (GAD) 65 are commonly observed in patients suffering from type 1 diabetes as well as stiff-person syndrome (SPS), a disorder that affects the CNS, and a variant of SPS, progressive encephalomyelitis with rigidity and myoclonus. Although there is a considerable amount of data focusing on the role of GAD65-specific CD4(+) T cells in type 1 diabetes, little is known about their role in SPS. In this study, we show that mice possessing a monoclonal GAD65-specific CD4(+) T cell population (4B5, PA19.9G11, or PA17.9G7) develop a lethal encephalomyelitis-like disease in the absence of any other T cells or B cells. GAD65-reactive CD4(+) T cells were found throughout the CNS in direct concordance with GAD65 expression and activated microglia: proximal to the circumventricular organs at the interface between the brain parenchyma and the blood-brain barrier. In the presence of B cells, high titer anti-GAD65 autoantibodies were generated, but these had no effect on the incidence or severity of disease. In addition, GAD65-specific CD4(+) T cells isolated from the brain were activated and produced IFN-gamma. These findings suggest that GAD65-reactive CD4(+) T cells alone mediate a lethal encephalomyelitis-like disease that may serve as a useful model to study GAD65-mediated diseases of the CNS.

Minimal Change Nephrotic Syndrome With Stiff-Person Syndrome: Is There a Link?

Stiff-person syndrome is a rare, likely immune-mediated neurological disorder characterized by painful spasms and progressive symmetric rigidity of the axial and proximal limb muscles. Rigidity of truncal muscles and continuous contraction of the agonist and antagonist muscles caused by involuntary motor-unit firing at rest are the hallmarks of stiff-person syndrome. Immunosuppressive therapy has induced remission in patients with stiff-person syndrome. We report a patient with stiff-person syndrome with minimal change nephrotic syndrome (MCNS). The pathophysiologic states of stiff-person syndrome and MCNS are unclear. T-Cell-dependent mechanisms are highly suspected for the pathogenesis of both. The diagnosis of stiff-person syndrome was made on the basis of clinical and laboratory findings, and both MCNS and stiff-person syndrome resolved completely with immunosuppressive therapy. To our knowledge, this is the first case of stiff-person syndrome in association with MCNS in the literature.

Stiff-person Syndrome

Stiff-person syndrome (SPS) is a progressive neurologic disorder characterized by 1) stiffness that is prominent in axial muscles, with co-contraction of agonist and antagonist muscles; 2) sudden episodic spasms; and 3) absence of another disease that causes similar symptoms. The diagnosis of SPS is based on clinical grounds and requires a high degree of suspicion. The diagnosis is, however, aided by electromyography, which demonstrates motor unit firing at rest simultaneously from the agonist and antagonist muscles, and by high serum titers of antibodies against glutamic acid decarboxylase (GAD), the rate-limiting enzyme for the synthesis of gamma-aminobutyric acid (GABA), which is the brain's main inhibitory neurotransmitter. The reduced GABA level in the brain and cerebrospinal fluid explains the patients' stiffness and justifies the clinical improvement observed by drugs enhancing GABAergic transmission. The association of SPS with other autoimmune disorders or autoantibodies, the intrathecal GAD-specific immunoglobulin G antibody synthesis, and the suppression of GABA by the patient's antibodies supports the autoimmune nature of SPS and justifies the use of immunotherapies. At present, GABA-enhancing agents, such as benzodiazepines, valproate, vigabatrin, tiagabine, gabapentin, and baclofen, provide symptomatic relief. Plasmapheresis, steroids, and periodic intravenous immunoglobulin infusions provide additional and lasting benefit. In this article, the treatment options for patients with SPS are discussed based on the authors' experience and that of others. The beneficial effects from the first controlled study conducted in SPS using intravenous immunoglobulin are presented.

T-cell reactivity to glutamic acid decarboxylase in stiff-man syndrome and cerebellar ataxia associated with polyendocrine autoimmunity

Antibodies to glutamic acid decarboxilase (GAD-Abs) are present in the serum of 60-80% of newly diagnosed type 1 diabetes (DM1) patients and patients with autoimmune polyendocrine syndrome (APS) associated with DM1. Higher titre of GAD-Abs are also present in the serum of 60% of patients with stiff-man syndrome (SMS) and all reported patients with cerebellar ataxia associated with polyendocrine autoimmunity (CAPA). Several studies suggest that GAD-Abs may play a critical role in the pathogenesis of SMS and CAPA but little is known about T-cell responsiveness to GAD-65 in these neurological diseases. To analyse cell-mediated responses to GAD, we studied the peripheral blood lymphocyte proliferation and cytokine responses to recombinant human GAD-65 in 5 patients with SMS, 6 with CAPA, 9 with DM1, 8 with APS and 15 control subjects. GAD-65-specific cellular proliferation was significantly higher in SMS than in CAPA, DM1, APS or controls. In contrast, only T cells from CAPA patients showed a significantly high production of interferon-gamma after GAD stimulation, compared to all other patients and controls. No differences were found for IL-4 production. These results suggest that, despite similar humoral autoreactivity, cellular responses to GAD are different between SMS and CAPA, with a greater inflammatory response in CAPA, and this difference may be relevant to the pathogenesis of these diseases.

Type 1 diabetes mellitus and epilepsia partialis continua in a 6-year-old boy with elevated anti-GAD65 antibodies

A 6-year-old boy presented with epilepsia partialis continua 6 months after diagnosis of type 1 diabetes. Anti-glutamic acid decarboxylase 65 antibodies were found in his serum and cerebrospinal fluid. Anti-epileptic agents did not improve his seizures. High-dose steroids, plasmapheresis, and intravenous immunoglobulin resulted in decreased anti-glutamic acid decarboxylase 65 antibody levels and resolution of his seizures.

Atypical low back pain: stiff-person syndrome

Stiff-person syndrome was diagnosed in a patient with chronic low back pain. The diagnosis of this rare neurological condition rests mainly on the clinical findings of axial and proximal limb rigidity, increased lumbar lordosis often accompanied with pain, and normal neurological findings apart from brisk deep tendon reflexes. Electromyography of the lumbar paraspinal muscles shows motor unit firing at rest with normal appearance of the motor unit potentials. Titers of antibody to glutamic acid decarboxylase are elevated. Diazepam is the treatment of reference. Physical therapy can substantially improve quality of life.

Immune reactivity to glutamic acid decarboxylase 65 in stiffman syndrome and type 1 diabetes mellitus

BACKGROUND

The immune response to an isoform of glutamic acid decarboxylase (GAD), GAD65, is associated with two clinically distinct diseases, stiff-man syndrome (SMS) and type 1 (insulin-dependent) diabetes mellitus. We sought to identify differences in the cellular and humoral immune responses to GAD in these two diseases.

METHODS

We compared T-cell responses in 14 SMS patients with axial disease and 17 patients with type 1 diabetes.

FINDINGS

Peripheral blood T cells of eight SMS patients recognised different immunodominant epitopes of GAD65 compared with T cells from 17 patients with type 1 diabetes. GAD regions 81-171 and 313-403 induced a dominant T-cell response in six of eight patients with SMS but in only one of 17 patients with type 1 diabetes (p=0.001). No SMS patients responded dominantly to GAD fragments 161-243 and 473-555 compared with ten patients with type 1 diabetes (p=0.008). GAD antibodies were detected in 11 of 14 SMS patients (seven with diabetes) and 11 of 17 patients with type 1 diabetes; IgG1 was dominant in both groups. SMS patients, however, were more likely than patients with diabetes to have isotypes other than IgG1 (p=0.03), in particular, IgG4 or IgE isotypes, which were not detected in patients with type 1 diabetes (p=0.012).

INTERPRETATION

Our findings indicate differences between patients with SMS and type 1 diabetes in cellular (epitope recognition) and humoral (isotype pattern) responses to GAD65. Thus the same autoantigen can elicit distinct immune responses in patients with SMS, even when associated with diabetes, compared with patients with type 1 diabetes.

The stiff-person syndrome: an autoimmune disorder affecting neurotransmission of gamma-aminobutyric acid

The stiff-person syndrome, a rare and disabling disorder, is characterized by muscle rigidity and episodic spasms that involve axial and limb musculature. Continuous contraction of agonist and antagonist muscles caused by involuntary motor-unit firing at rest are the hallmark clinical and electrophysiologic signs of the disease. Except for global muscle stiffness, results of neurologic examination are usually normal. Results of conventional computed tomography and magnetic resonance imaging of the brain are also normal. The cause of the stiff-person syndrome is unknown; however, an autoimmune pathogenesis is suspected because of 1) the presence of antibodies against glutamic acid decarboxylase (GAD), the rate-limiting enzyme for the synthesis of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA); 2) the association of the disease with other autoimmune conditions; 3) the presence of various autoantibodies; and 4) a strong immunogenetic association. Anti-GAD antibodies, which are found in high titers in most patients, seem to be directed against conformational forms of GAD. New evidence suggests that these antibodies may be pathogenic because they interfere with the synthesis of GABA. In addition, a reduction in brain levels of GABA, which is prominent in the motor cortex, has been demonstrated with magnetic resonance spectroscopy in patients with the stiff-person syndrome. The stiff-person syndrome is clinically elusive but potentially treatable and should be considered in patients with unexplained stiffness and spasms. Drugs that enhance GABA neurotransmission, such as diazepam, vigabatrin, and baclofen, provide mild to modest relief of clinical symptoms. Immunomodulatory agents, such as steroids, plasmapheresis, and intravenous immunoglobulin, seem to offer substantial improvement. Results of an ongoing controlled trial will elucidate the role of these agents in the treatment of the disease.