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Background:Circulating autoantibodies (AB) against brain-antigens, often deemed pathological, receive increasing attention. We assessed predispositions and seroprevalence/characteristics of 49 AB in >7000 individuals.Methods:Exploratory cross-sectional cohort study, investigating deeply phenotyped neuropsychiatric patients and healthy individuals of GRAS Data Collection for presence/characteristics of 49 brain-directed serum-AB. Predispositions were evaluated through GWAS of NMDAR1-AB carriers, analyses of immune check-point genotypes, APOE4 status, neurotrauma. Chi-square, Fisher’s exact tests and logistic regression analyses were used.Results:Study of N=7025 subjects (55.8% male; 41±16 years) revealed N=1133 (16.13%) carriers of any AB against 49 defined brain-antigens. Overall, age dependence of seroprevalence (OR=1.018/year; 95% CI [1.015-1.022]) emerged, but no disease association, neither general nor with neuropsychiatric subgroups. Males had higher AB seroprevalence (OR=1.303; 95% CI [1.144-1.486]). Immunoglobulin class (N for IgM:462; IgA:487; IgG:477) and titers were similar. Abundant were NMDAR1-AB (7.7%). Low seroprevalence (1.25%-0.02%) was seen for most AB (e.g. amphiphysin, KCNA2, ARHGAP26, GFAP, CASPR2, MOG, Homer-3, KCNA1, GLRA1b, GAD65). Non-detectable were others. GWAS of NMDAR1-AB carriers revealed three genome-wide significant SNPs, two intergenic, one in TENM3, previously autoimmune disease-associated. Targeted analysis of immune check-point genotypes (CTLA4, PD1, PD-L1) uncovered effects on humoral anti-brain autoimmunity (OR=1.55; 95% CI [1.058-2.271]) and disease likelihood (OR=1.43; 95% CI [1.032-1.985]). APOE4 carriers (∼19%) had lower seropositivity (OR=0.766; 95% CI [0.625-0.933]). Neurotrauma predisposed to NMDAR1-AB seroprevalence (IgM: OR=1.599; 95% CI [1.022-2.468]).Conclusions:Humoral autoimmunity against brain-antigens, frequent across health and disease, is predicted by age, gender, genetic predisposition, and brain injury. Seroprevalence, immunoglobulin class, or titers do not predict disease.

IgG of type 1 anti-neuronal nuclear antibody (ANNA-1, anti-Hu) specificity is a serological marker of paraneoplastic neurological autoimmunity (including enteric/autonomic) usually related to small-cell lung carcinoma. We show here that IgG isolated from such sera and also affinity-purified anti-HuD label enteric neurons and cause an immediate spike discharge in enteric and visceral sensory neurons. Both labelling and activation of enteric neurons was prevented by preincubation with the HuD antigen. Activation of enteric neurons was inhibited by the nicotinic receptor antagonists hexamethonium and dihydro-β-erythroidine and reduced by the P2X antagonist pyridoxal phosphate-6-azo (benzene-2,4-disulfonic acid (PPADS) but not by the 5-HT3 antagonist tropisetron or the N-type Ca-channel blocker ω-Conotoxin GVIA. Ca(++) imaging experiments confirmed activation of enteric neurons but not enteric glia. These findings demonstrate a direct excitatory action of ANNA-1, in particular anti-HuD, on visceral sensory and enteric neurons, which involves nicotinic and P2X receptors. The results provide evidence for a novel link between nerve activation and symptom generation in patients with antibody-mediated gut dysfunction.

Autoantibodies (AB) against N-methyl-D-aspartate receptor subunit NR1 (NMDAR1) are highly seroprevalent in health and disease. Symptomatic relevance may arise upon compromised blood-brain barrier (BBB). However, it remained unknown whether circulating NMDAR1 AB appear in the cerebrospinal fluid (CSF). Of n = 271 subjects with CSF-serum pairs, 26 were NMDAR1 AB seropositive, but only 1 was CSF positive. Contrariwise, tetanus AB (non-brain-binding) were present in serum and CSF of all subjects, with CSF levels higher upon BBB dysfunction. Translational mouse experiments proved the hypothesis that the brain acts as an 'immunoprecipitator'; simultaneous injection of NMDAR1 AB and the non-brain-binding green fluorescent protein AB resulted in high detectability of the former in brain and the latter in CSF.

The aim of this study was to evaluate the pathological significance of antibodies against cornea and inner ear tissue in the development of audiovestibular and ocular symptoms in patients with Cogan's syndrome (CS). We analysed the serum of 5 CS patients for binding of IgM and IgG to fresh cryosections of rat labyrinth (semicircular canals, ampulla, utricle, saccule) and cornea by indirect immunofluorescence (IF). The predominant pattern of anti-corneal IgM was staining of the superficial cell layer of the non-keratinizing squamous epithelium. IgM against cornea was found in 3 patients, all of whom had bilateral inflammatory eye signs at the start of the disease. However, IgM was also detected in the chronic stage of the disease when no clinical signs of eye involvement were apparent. The study includes the first follow-up examination of anti-corneal IgM and IgG antibodies during a complete episode of active CS. During the first episode of CS in 1 patient, anti-corneal IgM became detectable 1 week after the onset of interstitial keratitis and 3 weeks after the onset of audiovestibular symptoms. It increased over several weeks and then fell to very low levels. However, at no time was anti-corneal IgG found. In the course of follow-up examinations, the serum of 4 patients intermittently contained low titre IgG antibodies against inner ear labyrinthine tissue, but without any clear correlation with the active stages of CS. In addition, high-resolution MRI (HR-MRI) of the inner ear was performed in the acute and chronic stages of CS to evaluate the activity of CS. In the acute stage, HR-MRI revealed abnormal MRI signals in the vestibule, semicircular canals, vestibular nerve, or cochlea. In the chronic stage, patients showed narrowing or occlusion of semicircular canals and the cochlea on the 3D-CISS images, but no high signal lesions (T1) and no enhancement. Antibodies against cornea or labyrinthine tissue were not consistently detected in CS and the level of organ-specific antibodies did not correlate with the activity of the disease.

Recently, several novel autoantibodies have been identified which are closely associated with different subtypes of autoimmune encephalitis. These antibodies are directed against structures located on the neuronal cell surface: glutamate receptors (types NMDA and AMPA), GABA Breceptors, as well as the voltage-gated potassium channel-associated proteins LGI1 and CASPR2. They are much more common than the classical paraneoplastic antibodies (anti-Hu,-Yo,-Ri,-Ma,-CV2,-amphiphysin), less frequently associated with a tumour, and the corresponding clinical syndromes respond significantly better to immunotherapy. Monospecific detection of these autoantibodies in the serum or cerebrospinal fluid of patients is primarily performed by indirect immunofluorescence using transfected HEK293 cell lines recombinantly expressing the membrane-associated target antigens. Owing to the symptom overlap of the respective disorders, it is highly appropriate to determine these parameters in parallel for each patient (autoantibody profiles). Early diagnosis (substantially supported by the serological laboratory), the immediate initiation of immunotherapeutic intervention and, in cases of paraneoplastic aetiology, tumour resection are crucial for prognosis. In our own investigations, antibodies against glutamate receptors (type NMDA) are most frequently found among the newly identified forms of autoimmune encephalitis, accounting for 42% of cases. In laboratory practice, one-third of positive reactions were caused by an autoantibody whose determination was not requested by the clinician. Considering the clinical significance of a positive result, these findings substantiate the need to implement multiparametric serological test systems in this diagnostic area. © 2011 by Walter de Gruyter.

To investigate the possibility of an autoimmune mechanism in idiopathic bilateral vestibulopathy (IBV), we screened patients’ sera for antibodies against inner ear structures. IgG antibodies against membranous labyrinth (ampulla, semicircular canals, saccule and utricle) were detected in 8 of 12 patients by immunofluorescence on rat inner ear cryosections. All but one serum of 22 healthy controls and the sera of 6 patients with known autoimmune disorders showed only background staining. Low-titre anti-nuclear IgM antibodies were present in three control sera and one IBV serum. High-titre anti-nuclear IgM was found in a patient with lupus erythematosus and in one with scleroderma. Anti-nuclear IgM was not organ-specific. No human serum used contained detectable anti-vascular preformed antibodies. Cross-reactivity to sections of liver, kidney, cornea, brain and skeletal muscle was absent. Double-staining for IgG and F-actin, the primary constituent of hair cell cilia, did not show predominant Ig-coating of sensory hair cells. Immunosuppressive therapy in 3 IBV patients did not improve the disorder, probably owing to irreversible loss of sensory and neural structures. These data suggest that the bulk of anti-labyrinthine autoantibodies may be an epiphenomenon, yet a small subgroup of organ-specific autoantibodies may synergize with a cellular response in the development of vestibular lesions.

The catalytic zinc ion of astacin, a prototypical metalloproteinase from crayfish, has been substituted by Co(II), Cu(II), Hg(II), and Ni(II) in order to probe the role of the metal for both catalysis and structure. Compared to Zn(II)-astacin, Co(II)- and Cu(II)-astacin display enzymatic activities of about 140 and 37%, respectively, while Ni(II)- and Hg(II)-astacin are almost inactive. The electron paramagnetic resonance spectrum of Cu(II)-astacin is typical of 5-fold coordinated copper(II), and its intense absorption maxima at 445 and 325 nm are probably due to ligand-metal charge-transfer transitions involving Tyr-149. This residue had been identified previously by x-ray crystallography of the zinc enzyme as a zinc ligand, in addition to three imidazoles and a glutamic acid-bound water molecule. We present now the refined high-resolution x-ray crystal structures of Cu(II)-, Co(II)-, and Ni(II)-astacin, which exhibit a virtually identical protein framework to the previously analyzed structures of Zn(II)-, apo-, and Hg(II)-astacin. In Co(II)- and Cu(II)-astacin, the metal is penta-coordinated similarly to the native zinc enzyme. In the Ni(II) derivative, however, an additional solvent molecule expands the metal coordination sphere to a distorted octahedral ligand geometry, while in Hg(II)-astacin, no ordered solvent molecule at all is observed in the inner coordination sphere of the metal. This indicates a close correlation between catalytic properties and ground-state metal coordination of astacin.