Mateusz Makuch

Intracellular and non-neuronal targets of voltage-gated potassium channel complex antibodies

Objectives Autoantibodies against the extracellular domains of the voltage-gated potassium channel (VGKC) complex proteins, leucine-rich glioma-inactivated 1 (LGI1) and contactin-associated protein-2 (CASPR2), are found in patients with limbic encephalitis, faciobrachial dystonic seizures, Morvans syndrome and neuromyotonia. However, in routine testing, VGKC complex antibodies without LGI1 or CASPR2 reactivities (double-negative) are more common than LGI1 or CASPR2 specificities. Therefore, the target(s) and clinical associations of double-negative antibodies need to be determined. Methods Sera (n=1131) from several clinically defined cohorts were tested for IgG radioimmunoprecipitation of radioiodinated α-dendrotoxin (125I-αDTX)-labelled VGKC complexes from mammalian brain extracts. Positive samples were systematically tested for live hippocampal neuron reactivity, IgG precipitation of 125I-αDTX and 125I-αDTX-labelled Kv1 subunits, and by cell-based assays which expressed Kv1 subunits, LGI1 and CASPR2. Results VGKC complex antibodies were found in 162 of 1131 (14%) sera. 90 of these (56%) had antibodies targeting the extracellular domains of LGI1 or CASPR2. Of the remaining 72 double-negative sera, 10 (14%) immunoprecipitated 125I-αDTX itself, and 27 (38%) bound to solubilised co-expressed Kv1.1/1.2/1.6 subunits and/or Kv1.2 subunits alone, at levels proportionate to VGKC complex antibody levels (r=0.57, p=0.0017). The sera with LGI1 and CASPR2 antibodies immunoprecipitated neither preparation. None of the 27 Kv1-precipitating samples bound live hippocampal neurons or Kv1 extracellular domains, but 16 (59%) bound to permeabilised Kv1-expressing human embryonic kidney 293T cells. These intracellular Kv1 antibodies mainly associated with non-immune disease aetiologies, poor longitudinal clinical–serological correlations and a limited immunotherapy response. Conclusions Double-negative VGKC complex antibodies are often directed against cytosolic epitopes of Kv1 subunits and occasionally against non-mammalian αDTX. These antibodies should no longer be classified as neuronal-surface antibodies. They consequently lack pathogenic potential and do not in themselves support the use of immunotherapies.

Elevated Serum IgG4 Levels in Diagnosis, Treatment Response, Organ Involvement, and Relapse in a Prospective IgG4-Related Disease UK Cohort.

OBJECTIVES:Elevated serum immunoglobulin G4 (IgG4) levels have been associated with autoimmune pancreatitis and IgG4-related disease (IgG4-RD) for over a decade. However, an elevated serum IgG4 is not specific for the disease. There have been inconsistent reports of its use in diagnosis, as a marker of disease relapse, and its relationship to organ involvement in retrospective cohorts. The aims of this study were to ascertain conditions that are associated with an elevated serum IgG4 and to investigate the role of IgG4 in diagnosis, relapse, and organ involvement in a prospective cohort of patients with IgG4-RD.METHODS:We evaluated serum IgG4 measurements in the Oxford Immunology Laboratory over 6 years. Patients in whom serum IgG4 was requested to differentiate IgG4-RD from other diseases were recruited into a longitudinal follow-up study to determine final diagnosis. In a prospective cohort of IgG4-RD patients, organ involvement, response to therapy, and disease relapse were determined.RESULTS:Two thousand and sixty-seven samples from 1,510 patients had serum IgG4 measured. Of these, IgG4 was elevated (≥1.4 g l−1) in 243 (16.1%) patients. The main indication (85.6%) was to distinguish between IgG4-RD and non-IgG4-RD conditions. Only 5.1% of patients who had serum IgG4 measured for this purpose had a final diagnosis of IgG4-RD. Of those with an elevated serum IgG4, 22.4% met IgG4-RD diagnostic criteria. Serum IgG4 was elevated in 48 (82.8%) of IgG4-RD patients. An IgG4 cutoff of 1.4 g l−1 gave a sensitivity of 82.8% and specificity of 84.7% to diagnose IgG4-RD. Increasing this to 2.8 g l−1 increased specificity to 96.2% and negative predictive value to 97.7%, with a lower sensitivity of 56.9% and positive predictive value of 44.5%. Serum IgG4 levels fell with corticosteroid therapy, but this was not disease-specific. A serum IgG4 of ≥2.8 g l−1 at diagnosis was associated with multi-organ involvement and risk of relapse.CONCLUSIONS:Serum IgG4 levels are elevated in multiple non-IgG4-RD inflammatory and malignant conditions, with less than one-quarter of those with an elevated IgG4 meeting IgG4-RD diagnostic criteria. A serum IgG4 of ≥2.8 g l−1 is useful in distinguishing between IgG4-RD and non-IgG4-RD diagnoses, predicting multiple-organ involvement and risk of relapse in IgG4-RD.

Increased IgG4 responses to multiple food and animal antigens indicate a polyclonal expansion and differentiation of pre-existing B cells in IgG4-related disease

Background IgG4-related disease (IgG4-RD) is a systemic fibroinflammatory condition, characterised by an elevated serum IgG4 concentration and abundant IgG4-positive plasma cells in the involved organs. An important question is whether the elevated IgG4 response is causal or a reflection of immune-regulatory mechanisms of the disease. Objectives To investigate if the IgG4 response in IgG4-RD represents a generalised polyclonal amplification by examining the response to common environmental antigens. Methods Serum from 24 patients with IgG4-RD (14 treatment-naive, 10 treatment-experienced), 9 patients with primary sclerosing cholangitis and an elevated serum IgG4 (PSC-high IgG4), and 18 healthy controls were tested against egg white and yolk, milk, banana, cat, peanut, rice and wheat antigens by radioimmunoassay. Results We demonstrated an elevated polyclonal IgG4 response to multiple antigens in patients with IgG4-RD and in PSC-high IgG4, compared with healthy controls. There was a strong correlation between serum IgG4 and antigen-specific responses. Responses to antigens were higher in treatment-naive compared with treatment-experienced patients with IgG4-RD. Serum electrophoresis and immunofixation demonstrated polyclonality. Conclusions This is the first study to show enhanced levels of polyclonal IgG4 to multiple antigens in IgG4-RD. This supports that elevated IgG4 levels reflect an aberrant immunological regulation of the overall IgG4 response, but does not exclude that causality of disease could be antigen-driven.

The importance of early immunotherapy in patients with faciobrachial dystonic seizures

Faciobrachial dystonic seizures (FBDS) are the first adult-onset autoantibody-mediated epilepsy. Thompson et al. describe 103 patients with FBDS, and show that seizures are responsive to immunotherapy, with early seizure cessation reducing long-term disability and preventing cognitive impairment. Potential pathogenic mechanisms include complement fixation and LGI1-ADAM22 complex internalisation.

Increases in IgE, Eosinophils, and Mast Cells Can be Used in Diagnosis and to Predict Relapse of IgG4-Related Disease.

BACKGROUND & AIMS: IgG subclass 4–related disease (IgG4‐RD) is characterized by increased serum levels of IgG4 and infiltration of biliary, pancreatic, and other tissues by IgG4‐positive plasma cells. We assessed the prevalence of allergy and/or atopy, serum, and tissue IgE antibodies, and blood and tissue eosinophils in patients with IgG4‐RD. We investigated the association between serum IgE and diagnosis and relapse of this disease. METHODS: We performed a prospective study of 48 patients with IgG4‐RD, 42 patients with an increased serum level of IgG4 with other inflammatory and autoimmune conditions (disease control subjects), and 51 healthy individuals (healthy control subjects) recruited from Oxford, United Kingdom from March 2010 through March 2014, and followed for a median of 41 months (range, 3–73 months). Serum levels of immunoglobulin were measured at diagnosis, during steroid treatment, and at disease relapse for patients with IgG4‐RD; levels at diagnosis were compared with baseline levels of control subjects. Allergen‐specific IgEs were measured using the IgE ImmunoCAP. Levels and distribution of IgG4 and IgE antibodies in lymphoid, biliary, and pancreatic tissues from patients with IgG4‐RD and disease control subjects were measured by immunohistochemistry. We analyzed data using the Spearman rank correlation and receiver operating characteristic curves. RESULTS: Serum levels of IgG4 increased to 1.4 g/L or more, and IgE increased to 125 kIU/L or more, in 81% and 54% of patients with IgG4‐RD, respectively, compared with 6% and 16% of healthy control subjects (P < .0001). Peripheral blood eosinophilia was detected in 38% of patients with IgG4‐RD versus 9% of healthy control subjects (P = .004). Of patients with IgG4‐RD, 63% had a history of allergy and 40% had a history of atopy with an IgE‐specific response; these values were 60% and 53% in patients with increased serum levels of IgE (P < .05). Level of IgE at diagnosis >480 kIU/L distinguished patients with IgG4‐RD from disease control subjects with 86% specificity, 36% sensitivity, and a likelihood ratio of 3.2. Level of IgE at diagnosis >380 kIU/L identified patients with disease relapse with 88% specificity, 64% sensitivity, and a likelihood ratio of 5.4. IgE‐positive mast cells and eosinophilia were observed in lymphoid, biliary, and pancreatic tissue samples from 50% and 86% of patients with IgG4‐RD, respectively. CONCLUSIONS: In a prospective study, we associated IgG4‐RD with allergy, atopy, eosinophilia, increased serum levels of IgE, and IgE‐positive mast cells in lymphoid, biliary, and pancreatic tissue. An IgE‐mediated allergic response therefore seems to develop in most patients with IgG4‐RD; levels of IgE might be used in diagnosis and predicting relapse.

N-methyl-D-aspartate receptor antibody production from germinal center reactions: Therapeutic implications.

N‐methyl‐D‐aspartate receptor (NMDAR) antibody encephalitis is mediated by immunoglobulin G (IgG) autoantibodies directed against the NR1 subunit of the NMDAR. Around 20% of patients have an underlying ovarian teratoma, and the condition responds to early immunotherapies and ovarian teratoma removal. However, despite clear therapeutic relevance, mechanisms of NR1‐IgG production and the contribution of germinal center B cells to NR1‐IgG levels are unknown.

Condition-dependent generation of aquaporin-4 antibodies from circulating B cells in neuromyelitis optica

Aquaporin-4 antibodies are pathogenic in neuromyelitis optica spectrum disorders (NMOSD). Wilson et al. show that circulating memory and naïve B cells from patients can differentiate to produce aquaporin-4 antibodies under conditions chosen to mimic aspects of NMOSD. This platform should direct rationale immunotherapy in NMOSD and other antibody-mediated conditions.

No evidence to support a role for Helicobacter pylori infection and plasminogen binding protein in autoimmune pancreatitis and IgG4-related disease in a UK cohort

Background and objectives Helicobacter pylori (H.pylori) plasminogen binding protein (PBP) has been proposed as an antigen triggering autoimmune pancreatitis (AIP), the pancreatic manifestation of IgG4-related disease (IgG4-RD). We investigated exposure to H. pylori infection, cytokine response and immunological memory to H. pylori PBP in a prospective IgG4-RD cohort in the UK. Methods Clinical and endoscopic evidence of peptic ulceration, serological H. pylori exposure and serum IgG4 levels were obtained in 55 IgG4-RD patients and 52 disease controls (DC) with autoimmune or inflammatory conditions with an elevated serum IgG4. Gastric and duodenal tissues were assessed for H. pylori and immunostained for IgG4. B and T cell ELISpot and cytokine luminex assays were used to detect immune responses to H. pylori PBP. Results 85% of IgG4-RD patients had pancreatic and/or biliary disease, 89% had extra-pancreatic manifestations, and 84% had an increased serum IgG4. Clinical dyspepsia (35.2%), gastritis (58%), peptic ulceration (7.4%) and H. pylori colonisation (24%) in IgG4-RD was similar to DC. In IgG4-RD, gastric tissue contained a chronic inflammatory infiltrate with a low IgG4+ plasma-cell count (<10/HPF; range 1–4/HPF), and duodenal specimens had an increased IgG4 count (>10/HPF; range 7–54) compared with DC (p < 0.01). Th1 and Th2 cytokine response and immunological B-cell memory to H. pylori PBP did not differ between IgG4-RD and DC. Conclusions In a prospective UK cohort, the prevalence of gastric ulceration, exposure to H. pylori, cytokine response and immunological memory to H. pylori PBP did not differ in IgG4-RD patients compared with DC. This study does not support a role for H. pylori PBP as a microbial antigen in IgG4-RD. Keywords for abstract Peptic ulceration, Antigens, B cells, T cells, Interleukins, Helicobacter pylori.

ONGOING GERMINAL CENTRE REACTIONS CONTRIBUTE TO N-METHYL-D-ASPARTATE RECEPTOR (NMDAR) ANTIBODY PRODUCTION IN NMDAR-ANTIBODY ENCEPHALITIS

Abstract Background Immunoglobulin G (IgG) against the NR1-subunit of the N-methyl-D-aspartate (NMDAR) receptor mediates NMDAR-antibody encephalitis (NMDAR-Ab-E). This multi-stage illness presents with an acute severe psychiatric syndrome, alongside other neurological features, similar to human and animal NMDAR antagonist models. The disease is associated with an ovarian teratoma in around 20% of cases. The cellular immunity underlying this disease is not well understood. While antibody-modifying immunotherapies often promote disease resolution, the illness can be refractory to these treatments correlating with sub-optimal outcomes. NR1-IgG can be detected several years after clinical resolution, which may be via ongoing germinal centre reactions or the establishment of antibody-secreting cells as long-lived plasma cells in bone marrow niches. These two divergent models implicate use of differing immunotherapies to target these cells. Here we investigate the contribution of ongoing germinal centre reactions to disease progression, potentially informing disease mechanisms and guide targeted immunotherapy. Methods We hypothesised that recurrent antigen-driven germinal centre reactions would be associated with active generation of NR1-specific IgM and IgG and NR1-specific circulating B cells. We validated a NR1-IgM cell based assay establishing specificity cut-offs by screening healthy and disease control cohorts alongside a previously collected NMDAR-Ab-E cohort (n=46). Following this we went on to explore the temporal evolution of NR1-IgG and NR1-IgM titres in a prospective cohort (n=12). To investigate the lymphocyte characteristics, we stimulated ovarian teratoma lymphocytes and peripheral blood mononuclear cells (PBMCs) from multiple time points under varying cytokine conditions to understand whether these circulating cells showed capacity for NR1-IgG and IgM generation. Results We found a 43% prevalence rate of NR1-IgM in the historic cohort. We then confirmed that NR1-IgM binding was specific by its selective depletion after anti-IgM precipitation but not with protein G. In the prospective cohort, we noted often high titres of IgM (up to 1:500) most commonly early in the disease but persisting for around 2 years. NR1-IgM levels varied in titre alongside NR1-IgG spikes. Consistently, culture experiments of patient lymphocytes (PBMCs and tumour-derived) produced varying degrees of NR1-IgM and NR1-IgG under conditions associated with B cell proliferation. The NR1-IgG levels correlated with serum NR1-titres suggesting these circulating B cells made a proportional contribution to serum levels. Discussion Ongoing germinal centre reactions likely contribute much of the circulating NR1-specific B cell population in NMDAR-Ab-E. Autoimmunisation at these centres represents an as yet unexplored therapeutic target in this and potentially other autoimmune encephalopathies. Regional specificity of these reactions including lymph nodes draining sources of NR1-antigen require further direct evaluation.