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Background: Antibodies targeting membrane proteins play an important role in various autoimmune diseases of the nervous system. So far, assays allowing proper analysis of such autoantibodies are largely missing. A serum autoantibody to aquaporin 4 (AQP4) is associated with neuromyelitis optica (NMO). Although several assays are able to detect this autoantibody, they do not allow determination of the biological activity of anti-AQP4 antibodies., Objective: To develop a bioassay for quantification and characterization of human anti-AQP4 antibodies., Design, Setting, and Participants: We developed a novel bioassay for quantification and characterization of human anti-AQP4 antibodies based on high-level expression of native AQP4 (nAQP4) protein on the surface of human astroglioma cells. The test was validated in 2 independent cohorts of patients with NMO spectrum disease., Results: We detected anti-nAQP4-IgG with a sensitivity of 57.9% and specificity of 100% in patients with NMO spectrum diseases, suggesting that our bioassay is at least as sensitive and specific as the gold-standard NMO-IgG assay. The anti-AQP4 antibodies belonged predominantly to the IgG1 isotype and bound with high affinity to the extracellular domain of nAQP4. Our data suggest that the autoantibody exerts pathological properties because nAQP4-IgG-positive sera induced cell death of nAQP4-expressing cells by antibody-dependent cellular natural killer cell cytotoxic effect and complement activation. Furthermore, nAQP4-IgG titers strongly correlated with in vitro cytotoxic effect., Conclusions: In NMO, this assay may help to unravel the biological function of anti-nAQP4-IgG. Our findings demonstrate the potential of bioassays to characterize biologically relevant antibodies in human autoimmune diseases.

Objective: To determine if neutralizing antibodies (NAbs) against interferon beta from patients with multiple sclerosis (MS) cross-react with other type 1 interferons, especially endogenous interferon beta, and thus might impede the immune systems of affected patients., Design: Masked serum samples from MS patients were challenged in vitro against recombinant interferon beta-1a and interferon beta-1b, as well as human leukocyte interferon and fibroblast interferon, the latter representing endogenous interferon. The neutralizing capacity of serum samples on these type 1 interferons was assessed using a luciferase reporter gene assay. Randomly selected samples were titrated to further delineate the cross-reactivity of antibodies., Setting: University medical center in Düsseldorf, Germany., Patients: We randomly selected 150 samples from interferon beta-treated MS patients who had previously been tested for the presence of binding antibodies and NAbs., Main Outcome Measures: Neutralization of interferon beta bioactivity and cross-reactivity of anti-interferon beta antibodies., Results: Antibody-mediated neutralization of interferon beta bioactivity in vitro against recombinant interferon beta was observed in all serum samples that had previously tested positive for binding antibodies and NAbs. A neutralizing pattern comparable to that of recombinant interferon beta was observed when endogenous interferon was assessed, reflecting cross-reactivity of NAbs. No differences in neutralization between recombinant and endogenous interferon were observed with respect to the interferon beta preparation used for treatment. Furthermore, no neutralization of other type 1interferons by NAbs could be detected., Conclusions: A proportion of MS patients who are treated with recombinant interferon beta develop NAbs that also neutralize endogenous interferon. Because NAbs at high titers can persist for years, these antibodies may impede the immune system in affected MS patients regardless of their current treatment regimen.

Natalizumab (Tysabri) was the first monoclonal antibody approved for the treatment of relapsing forms of multiple sclerosis (MS). After its initial approval, 3 patients undergoing natalizumab therapy in combination with other immunoregulatory and immunosuppressive agents were diagnosed with progressive multifocal leukoencephalopathy (PML). The agent was later reapproved and its use restricted to monotherapy in patients with relapsing forms of MS. Since reapproval in 2006, additional cases of PML were reported in patients with MS receiving natalizumab monotherapy. Thus, there is currently no convincing evidence that natalizumab-associated PML is restricted to combination therapy with other disease-modifying or immunosuppressive agents. In addition, recent data indicate that risk of PML might increase beyond 24 months of treatment.

Objective: To study clinical and paraclinical effects of natalizumab in a patient with chronic inflammatory demyelinating polyneuropathy (CIDP)., Design: Case report., Setting: Department of Neurology, Heinrich-Heine University, Düsseldorf, Germany. Patient A patient with highly active CIDP who did not respond to standard therapies. Intervention Standard therapy then treatment with natalizumab (300 mg)., Main Outcome Measures: Clinical disability, magnetic resonance imaging, and saturation of the alpha(4) integrin on T lymphocytes., Results: T cells expressing the alpha(4) integrin were found in the inflamed peripheral nerve. Natalizumab bound with high affinity to the alpha(4) integrin on T lymphocytes in our patient. However, the patient's clinical condition deteriorated and as seen on magnetic resonance imaging without any measurable effect after treatment with this antibody., Conclusions: Although experimental evidence suggests that natalizumab could theoretically be effective in immune-mediated disorders of the peripheral nervous system, our patient with CIDP did not benefit from this therapeutic approach. Natalizumab cannot be recommended in CIDP at present and should only be explored in controlled clinical trials.

Objective: To describe 2 patients with relapsing-remitting multiple sclerosis (RRMS) receiving long-term treatment with the monoclonal antibody rituximab. The clinical and paraclinical efficacy of rituximab was demonstrated recently in a phase 2 clinical trial in patients with RRMS., Design: Case series., Setting: Tertiary care university medical center., Patients: Two young patients with highly active RRMS in whom standard therapy had failed before receiving rituximab for up to 48 months., Main Outcome Measures: Relapse rate, clinical disability, and results of magnetic resonance imaging., Results: Both patients tolerated rituximab treatment well and have been clinically stable throughout the study period., Conclusion: Long-term therapy with rituximab appears safe and effective in some patients with RRMS. Our observation should be confirmed in controlled long-term trials.

Acute disseminated encephalomyelitis (ADEM) is a monophasic autoimmune demyelinating disease of the central nervous system that typically follows a febrile infection or a vaccination. Children are predominantly affected. A plethora of viral and bacterial pathogens and a number of vaccinations have been associated with ADEM. Experimental animal studies indicate that both primary and secondary autoimmune responses contribute to central nervous system inflammation and subsequent demyelination. The clinical diagnosis of ADEM is strongly suggested by a close temporal relationship between an infectious incident or an immunization and the onset of leukoencephalopathic neurological symptoms. Paraclinical tests may support the diagnosis. Particularly helpful are acute signs of newly developed extensive, multifocal, subcortical white matter abnormalities on magnetic resonance images of the brain. The cerebrospinal fluid may disclose a mild lymphocytic pleocytosis and elevated albumin levels. Oligoclonal bands are not always present in ADEM and, if so, may be transient. The major differential diagnosis of ADEM is multiple sclerosis. Treatment options for ADEM consist of anti-inflammatory and immunosuppressive agents. In general, the disease is self-limiting and the prognostic outcome favorable. In the absence of widely accepted clinical or paraclinical diagnostic guidelines, a number of recently conducted observational case series have substantially broadened our understanding about the clinical phenotype, diagnosis, and prognosis of ADEM.