Kristin Rentzsch

Seroprevalence of autoantibodies against brain antigens in health and disease.

We previously reported an unexpectedly high seroprevalence (∼10%) of N‐methyl‐D‐aspartate‐receptor subunit‐NR1 (NMDAR1) autoantibodies (AB) in healthy and neuropsychiatrically ill subjects (N = 2,817). This finding challenges an unambiguous causal relationship of serum AB with brain disease. To test whether similar results would be obtained for other brain antigen‐directed AB previously connected with pathological conditions, we systematically screened serum samples of 4,236 individuals.

Multicentre comparison of a diagnostic assay: aquaporin-4 antibodies in neuromyelitis optica

Objective Antibodies to cell surface central nervous system proteins help to diagnose conditions which often respond to immunotherapies. The assessment of antibody assays needs to reflect their clinical utility. We report the results of a multicentre study of aquaporin (AQP) 4 antibody (AQP4-Ab) assays in neuromyelitis optica spectrum disorders (NMOSD). Methods Coded samples from patients with neuromyelitis optica (NMO) or NMOSD (101) and controls (92) were tested at 15 European diagnostic centres using 21 assays including live (n=3) or fixed cell-based assays (n=10), flow cytometry (n=4), immunohistochemistry (n=3) and ELISA (n=1). Results Results of tests on 92 controls identified 12assays as highly specific (0–1 false-positive results). 32 samples from 50 (64%) NMO sera and 34 from 51 (67%) NMOSD sera were positive on at least two of the 12 highly specific assays, leaving 35 patients with seronegative NMO/spectrum disorder (SD). On the basis of a combination of clinical phenotype and the highly specific assays, 66 AQP4-Ab seropositive samples were used to establish the sensitivities (51.5–100%) of all 21 assays. The specificities (85.8–100%) were based on 92 control samples and 35 seronegative NMO/SD patient samples. Conclusions The cell-based assays were most sensitive and specific overall, but immunohistochemistry or flow cytometry could be equally accurate in specialist centres. Since patients with AQP4-Ab negative NMO/SD require different management, the use of both appropriate control samples and defined seronegative NMOSD samples is essential to evaluate these assays in a clinically meaningful way. The process described here can be applied to the evaluation of other antibody assays in the newly evolving field of autoimmune neurology.

Serological diagnosis of autoimmune bullous skin diseases: Prospective comparison of the BIOCHIP mosaic-based indirect immunofluorescence technique with the conventional multi-step single test strategy

BackgroundVarious antigen-specific immunoassays are available for the serological diagnosis of autoimmune bullous diseases. However, a spectrum of different tissue-based and monovalent antigen-specific assays is required to establish the diagnosis. BIOCHIP mosaics consisting of different antigen substrates allow polyvalent immunofluorescence (IF) tests and provide antibody profiles in a single incubation.MethodsSlides for indirect IF were prepared, containing BIOCHIPS with the following test substrates in each reaction field: monkey esophagus, primate salt-split skin, antigen dots of tetrameric BP180-NC16A as well as desmoglein 1-, desmoglein 3-, and BP230gC-expressing human HEK293 cells. This BIOCHIP mosaic was probed using a large panel of sera from patients with pemphigus vulgaris (PV, n = 65), pemphigus foliaceus (PF, n = 50), bullous pemphigoid (BP, n = 42), and non-inflammatory skin diseases (n = 97) as well as from healthy blood donors (n = 100). Furthermore, to evaluate the usability in routine diagnostics, 454 consecutive sera from patients with suspected immunobullous disorders were prospectively analyzed in parallel using a) the IF BIOCHIP mosaic and b) a panel of single antibody assays as commonly used by specialized centers.ResultsUsing the BIOCHIP mosaic, sensitivities of the desmoglein 1-, desmoglein 3-, and NC16A-specific substrates were 90%, 98.5% and 100%, respectively. BP230 was recognized by 54% of the BP sera. Specificities ranged from 98.2% to 100% for all substrates. In the prospective study, a high agreement was found between the results obtained by the BIOCHIP mosaic and the single test panel for the diagnosis of BP, PV, PF, and sera without serum autoantibodies (Cohen’s κ between 0.88 and 0.97).ConclusionsThe BIOCHIP mosaic contains sensitive and specific substrates for the indirect IF diagnosis of BP, PF, and PV. Its diagnostic accuracy is comparable with the conventional multi-step approach. The highly standardized and practical BIOCHIP mosaic will facilitate the serological diagnosis of autoimmune blistering diseases.

Preexisting Serum Autoantibodies Against the NMDAR Subunit NR1 Modulate Evolution of Lesion Size in Acute Ischemic Stroke

Background and Purpose— Recently, we reported high seroprevalence (age-dependent up to >19%) of N-methyl-D-aspartate-receptor subunit NR1 (NMDAR1) autoantibodies in both healthy and neuropsychiatrically ill subjects (N=4236). Neuropsychiatric syndrome relevance was restricted to individuals with compromised blood–brain barrier, for example, apolipoprotein E4 (APOE4) carrier status, both clinically and experimentally. We now hypothesized that these autoantibodies may upon stroke be protective in individuals with hitherto intact blood–brain barrier, but harmful for subjects with chronically compromised blood–brain barrier. Methods— Of 464 patients admitted with acute ischemic stroke in the middle cerebral artery territory, blood for NMDAR1 autoantibody measurements and APOE4 carrier status as indicator of a preexisting leaky blood–brain barrier was collected within 3 to 5 hours after stroke. Evolution of lesion size (delta day 7–1) in diffusion-weighted magnetic resonance imaging was primary outcome parameter. In subgroups, NMDAR1 autoantibody measurements were repeated on days 2 and 7. Results— Of all 464 patients, 21.6% were NMDAR1 autoantibody–positive (immunoglobulin M, A, or G) and 21% were APOE4 carriers. Patients with magnetic resonance imaging data available on days 1 and 7 (N=384) were divided into 4 groups according to NMDAR1 autoantibody and APOE4 status. Groups were comparable in all stroke-relevant presenting characteristics. The autoantibody+/APOE4− group had a smaller mean delta lesion size compared with the autoantibody−/APOE4- group, suggesting a protective effect of circulating NMDAR1 autoantibodies. In contrast, the autoantibody+/APOE4+ group had the largest mean delta lesion area. NMDAR1 autoantibody serum titers dropped on day 2 and remounted by day 7. Conclusions— Dependent on blood–brain barrier integrity before an acute ischemic brain injury, preexisting NMDAR1 autoantibodies seem to be beneficial or detrimental.

Co-occurrence of autoantibodies in healthy blood donors

Autoimmune diseases are rare, but their incidence has increased over the past decades. Interestingly, the co‐occurrence of autoimmune diseases is well documented; however, data on the presence of more than one specific autoantibody in healthy individuals are not available. Here, we investigated the prevalence of several autoantibodies in a cohort of over 6000 healthy persons. While individual autoantibodies were rarely detected (i.e. ranging from 0.3% for ANCA to 4.6% for anti‐TPO), the cumulative prevalence of the tested autoantibodies was as high as 10%. Furthermore, our results demonstrate co‐occurrence of ANA with specific autoantibodies that target TPO, CCP and Dsg1/3, while ANCA and autoantibodies to PCA and BP180/BP230 were not more frequent in ANA‐positive compared to ANA‐negative samples. This indicates that shared and independent mechanisms influence loss of tolerance to distinct sets of self‐antigens.

Routine detection of serum antidesmocollin autoantibodies is only useful in patients with atypical pemphigus.

Autoantibodies against the 3 desmocollin (Dsc; Dsc1‐Dsc3) isoforms have been described in different pemphigus variants. Here, we developed state‐of‐the‐art detection systems for serum anti‐Dsc1, Dsc2 and Dsc1 IgG and IgA. These assays were applied in 5 different cohorts including pemphigus vulgaris (PV) patients with compatible direct immunofluorescence (IF) microscopy but no reactivity against desmogleins 1 and 3 (n = 24) and sera from patients with autoimmune blistering diseases with positive direct IF microscopy taken at the time of diagnosis (n = 749). We found that detection of anti‐Dsc serum reactivity is not helpful in the routine diagnosis of PV, pemphigus foliaceus and paraneoplastic pemphigus but may be valuable in pemphigus vegetans.

Multiparametric serological testing in autoimmune encephalitis using computer-aided immunofluorescence microscopy (CAIFM).

Autoantibodies against neuronal cell surface antigens are tightly associated with immunotherapy-responsive autoimmune encephalitis, and a considerable number of corresponding autoantigens has been identified in recent years. Most patients initially present with overlapping symptoms, and a broad range of autoantibodies has to be considered to establish the correct diagnosis and initiate treatment as soon as possible to prevent irreversible and sometimes even life-threatening damage to the brain. Recombinant cell-based immunofluorescence allows to authentically present fragile membrane-associated surface antigens and, in combination with multiparametric analysis in the form of biochip mosaics, has turned out to be highly beneficial for parallel and prompt determination of anti-neuronal autoantibodies and comprehensive differential diagnostics. For the evaluation of recombinant cell-based IIFT, a semi-automated novel function was introduced into an established platform for computer-aided immunofluorescence microscopy. The system facilitates the microscopic analysis of the tests and supports the laboratory personnel in the rapid issuance of diagnostic findings, which is of major importance for autoimmune encephalitis patients since timely initiation of treatment may lead to their full recovery.

Development of a Recombinant Cell-Based Indirect Immunofluorescence Assay for the Determination of Autoantibodies against Soluble Liver Antigen in Autoimmune Hepatitis

Autoantibodies against soluble liver antigen (SLA) are specific markers for autoimmune hepatitis (AIH) type 1. In contrast to the determination of other AIH-associated autoantibodies by indirect immunofluorescence assay (IFA), detection of anti-SLA relied up to now on ELISA or immunoblot based on bacterially expressed recombinant protein. In order to develop a complementary IFA substrate, SLA isoform 1 was recombinantly produced in the human cell line HEK293 and controlled by a rabbit hyperimmune serum against SLA. The recombinant cells were used in IFA (RC-IFA) to analyze sera from 20 AIH patients with anti-SLA positivity predetermined by ELISA together with 80 controls (20 anti-SLA negative AIH, 15 primary biliary cirrhosis, 15 HCV, and 30 healthy blood donors). Using RC-IFA, anti-SLA was detected in all ELISA positive AIH sera but in none of the controls. Furthermore, a cytosolic fraction of HEK293 containing SLA was able to neutralize the autoantibodies in all positive sera in a dose-dependent manner. HEK293 cells expressing SLA are a valid substrate for the serodiagnosis of AIH relevant autoantibodies by IFA. In concert with cryosections of primate liver, rat kidney, rat liver, rat stomach, and HEp-2 cells, they enable the parallel determination of all autoantibodies associated with autoimmune liver diseases.

Assessment of aquaporin-4 (AQP4) antibody assays in European diagnostic centres

identified follicle-like structures containing B cells close to vessels and PDGFRb+ cells forming a reticular network expanding to the parenchyma. To find out if these structures could provide sufficient homing locations which support plasma cells to become long-lived, we performed 5-ethynyl-2′-deoxyuridine (EdU)-pulse experiments. During pulse, EdU is incorporated by dividing cells like plasma blasts. The detection of EdU-positive cells up to seven weeks after pulse suggests that niches in the CNS can favor survival of plasma cells. We then further analyzed the migration of plasma blasts to the CNS. Since the sphingosine-1-phosphate analogon FTY720 (fingolimod) is known to suppress immune cell trafficking, we performed EAE experiments under accompanying treatment with the drug. FTY720treated animals were resistant to EAE in contrast to control animals. Immunofluorescent histological findings confirmed that no immune cell infiltration took place in FTY720-treated animals and the protective effect of FTY720 was not due to retention of immune cells in spleen, lymph nodes or bone marrow, as proved by quantitative FACS analysis. Control mice displayed massive immune cell infiltration in the perivascular space and parenchyma of the CNS, some evidently of long-lived phenotype. These results can be useful to evaluate the therapeutic potential of targeting plasma cells in chronic neuroinflammation.

Treatment with interferon-beta does not induce anti-nuclear and anti-neuronal serum autoantibodies in multiple sclerosis patients

Type I interferons (IFNs) are known to enhance humoral immunity. Here, we investigated the prevalence and titer of anti-nuclear and anti-neuronal IgG autoantibodies in 71 relapsing-remitting MS patients classified based on their clinical response to IFNβ in paired sera obtained at baseline and after 12months of treatment. All samples were negative for antibodies against cytoplasmic rods/rings, synaptic proteins and paraneoplastic antibodies. Regarding anti-nuclear, anti-filament and anti-myelin antibodies, pre- and post-treatment prevalence and titers did not differ significantly between IFNβ responders and non-responders. Thus, pattern of anti-nuclear and anti-neuronal autoantibodies does not predict the response to IFNβ in MS patients.