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The ability to detect antibodies to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is currently under investigation with various performance characteristics and indications for use. In this article, we analyzed the ability of the Abbott SARS-CoV-2 immunoglobulin class G (IgG), EuroImmun SARS-CoV-2 enzyme-linked immunosorbent assay (ELISA) IgG, and EuroImmun SARS-CoV-2 ELISA immunoglobulin class A (IgA) kits to detect evidence of previous infection with SARS-CoV-2. We tested 49 known coronavirus disease-19 (COVID-19) patients and 111 prepandemic stored serology specimens. This resulted in a sensitivity of 95.9%, 100.0%, and 91.3% and a specificity of 98.2%, 98.2%, and 90.8% respectively, using manufacturer recommended cutoffs after inconclusive results (one for EuroImmun IgG and five for EuroImmun IgA) being excluded in the final statistical analyses. Cross-reactivity of hepatitis C virus seropositive specimens was observed resulting in false positives (p < 0.05). If a two-tiered algorithmic approach was applied, that is, testing with Abbott SARS-CoV-2 assay followed by EuroImmun SARS-CoV-2 IgG, 100% specificity and sensitivity could be obtained after six inconclusive results were excluded from data set before statistical analyses. Performance characteristics presented demonstrate the superior performance of IgG class antibodies for investigating previous infections. In addition, utilizing a second antibody test for supplementary testing may significantly enhance performance, particularly in lower prevalence settings.

IgA nephropathy (IgAN) is an autoimmune disease characterized by renal glomerular immunodeposits enriched for galactose-deficient IgA1 (Gd-IgA1; autoantigen) with the corresponding IgG autoantibodies. Despite the known contribution of Gd-IgA1 to IgAN, little is known concerning IgA1-secreting subpopulations responsible for autoantigen production. The goal of this study is to identify IgA1-secreting and membrane subpopulations from single-cell transcriptomic analysis. We developed a novel single-cell analytics workflow to discern cells expressing IgA1 secreted isoform or membrane-bound isoform. Multiple approaches were compared to assess immunoglobulin-isotype identity in single cells, and multiple immunoglobulin heavy-chain genes expressed in the same cells were found. To better identify specific immunoglobulin heavy-chain transcripts, we merged a software platform called Alteryx with the existing single-cell R toolkit program Seurat. This process allowed for improved calls on IgA1-secreting subpopulations based on secreting versus membrane splice-variant expression levels.

Purpose.To evaluate the significance of IgG detection to glycoprotein E of varicella-zoster virus (VZV) for the infection stage diagnosis.Materials and methods.Integration of literature data.Results.Analysis of literature data allows to make quite reasonable conclusion that the dynamics of IgG antibodies to glycoprotein E of VZV is subject to the general laws of the antibody productions in the course of infectious processes, although the final completion of this discussion the essential results of direct detection of the dynamics of these antibodies in various stages and forms of the indicated infection.

The mammalian intestine is home to trillions of microbes, and their colonization contributes to host physiology through the production of indispensable metabolites and competition against pathogens. However, it is also important to balance this symbiotic relationship, as overgrowth and translocation of microbes could trigger a fatal infection. IgA is the major immunoglobulin class produced and secreted in the intestine and is considered to play a pivotal role in maintaining homeostasis. In this review, we summarize recent studies exploring the interactions between IgA and the gut microbiota and explain how different types of IgA could coexist to regulate the gut microbiota. In particular, we discuss two important aspects of IgA in controlling the gut microbes: function and specificity. Differences in these two aspects appear attributable to how IgA is induced and are associated with the functions of IgA as well. Together, our review delineates a recent understanding of IgA–microbiome interactions and proposes a future direction to clarify its complexity.

Immunoglobulins (Igs) are complex glycoproteins that play critical functions in innate and adaptive immunity of all jawed vertebrates. Given the unique characteristics of mucosal barriers, secretory Igs (sIgs) have specialized to maintain homeostasis and keep pathogens at bay at mucosal tissues from fish to mammals. In teleost fish, the three main IgH isotypes, IgM, IgD and IgT/Z can be found in different proportions at the mucosal secretions of the skin, gills, gut, nasal, buccal, and pharyngeal mucosae. Similar to the role of mammalian IgA, IgT plays a predominant role in fish mucosal immunity. Recent studies in IgT have illuminated the primordial role of sIgs in both microbiota homeostasis and pathogen control at mucosal sites. Ten years ago, IgT was discovered to be an immunoglobulin class specialized in mucosal immunity. Aiming at this 10-year anniversary, the goal of this review is to summarize the current status of the field of fish Igs since that discovery, while identifying knowledge gaps and future avenues that will move the field forward in both basic and applied science areas.

Introduction: The detection of anti-double-stranded (ds) deoxyribonucleic acid (DNA) antibodies is one of the classification criteria for diagnosing systemic lupus erythematosus (SLE). Objective: To describe a quantitative enzyme-linked immunosorbent assay (ELISA) for detecting anti-dsDNA immunoglobulin class G (IgG) antibodies. Methods: The performance of ELISA was evaluated using the Crithidia luciliae indirect immunofluorescence test (CLIFT) as a reference. Anti-dsDNA IgG antibodies were screened by ELISA and CLIFT in serum samples from 127 patients with SLE, 56 patients with other diseases and 37 healthy persons. The Cochran Q test was used to compare the sensitivity and specificity of the reactions, with differences among the results being considered significant when p ≤ 0.05. Results: ELISA had a sensitivity of 92.9% and a specificity of 94.6%, whereas the sensitivity and specificity of CLIFT were 85.8% and 100%, respectively. ELISA was significantly more sensitive than CLIFT (p = 0.0027), whereas CLIFT was significantly more specific than ELISA (p = 0.0253). Conclusion: ELISA showed excellent results in terms of sensitivity and specificity, with a potential use in research and routine diagnostics.

Ischemic stroke provoke irreversible changes in the organism and fully recovery was not observed. Some reactivity of the haemostasis system were shoved during the acute phase of ischemic stroke as well as post few year. The idea was explored that specific autoantibody generated in the bloodstream during the acute phase and their existence in bloodstream past one year could provoke disease repetition. Fractions of immunoglobulin class G were separated: from the blood plasma of healthy donors, patients with atherothrombotic and cardioembolic ischemic stroke in acute phase of disease and the analogical fractions from the same patients one year past acute phase. The influence of the separated fractions on the process of ADF-induced healthy donor's platelets aggregation was observed. It was showed that impact of immunoglobulin class G was characterized by one-wave irreversible ADP-induced platelet aggregation. The maximum aggregation was shoved under influence of IgG fraction separated from the patients with AIS. This influence was on the 15 % more intensive in comparison with influence of IgG fraction separated from the healthy donors. One year past disease all tested IgG fractions provoked inhibition of platelets aggregation up to 25 %. The maximum inhibition of ADP-dependent healthy donor's platelets aggregation was provided by fraction separated from the patients with AIS one year past acute phase.

Purpose of review Humoral autoimmunity has gained highest interest in neurology and psychiatry. Despite numerous recent articles on this hot topic, however, the biological significance of natural autoantibodies (AB) and the normal autoimmune repertoire of mammals remained quite obscure. AB may contribute to disorder-relevant phenotypes and are even believed to induce diseases themselves, but the circumstances under which AB become pathogenic are not fully understood. This review will focus on the highly frequent AB against the N-methyl-d-aspartate receptor 1 (NMDAR1-AB) as an illustrating example and provide a critical overview of current work (please note that the new nomenclature, GluN1, is disregarded here for consistency with the AB literature). In particular, it will demonstrate how little is known at this point and how many conclusions are drawn based on small numbers of individuals, fragmentary experimental approaches or missing controls. Recent findings NMDAR1-AB were investigated by clinicians world-wide with numerous small studies and case reports appearing yearly. Many publications were on 'anti-NMDAR encephalitis' cases or tried to separate those from other NMDAR1-AB associated conditions. Original exclusivity claims (e.g. electroencephalogram, EEG or functional magnetic resonance imaging, fMRI findings) turned out not to be exclusive for 'anti-NMDAR encephalitis'. Systematic analyses of representative NMDAR1-AB positive sera of all immunoglobulin (Ig) classes showed comparable distribution of different epitopes, often polyspecific/polyclonal, across health and disease. Sophisticated imaging tools provided findings on synapse trafficking changes induced by NMDAR1-AB from psychotic subjects but still lack epitope data to support any claimed disorder link. Persistently high titers of NMDAR1-AB (IgG) in immunized mice with open blood-brain barrier (BBB)-induced psychosis-like symptoms but failed to induce inflammation in the brain. Knowledge on peripheral NMDAR, for example in the immune system, and on potential inducers of NMDAR1-AB is only slowly increasing. Summary The present knowledge on the (patho) physiological role of NMDAR1-AB is very limited and still characterized by adamant rumors. Much more experimental work and more solid and informative clinical reports, including large numbers of subjects and adequate control groups, follow-up investigations and interdisciplinary approaches will be necessary to obtain a better understanding of the significance of humoral autoimmunity in general (in focus here: NMDAR1-AB) and its disease-relevance in particular.

Autoantibodies of the IgG class against N-methyl-d-aspartate-receptor subunit NR1 (NMDAR1) were first described in anti-NMDAR encephalitis and seen as disease indicators. Recent work on together over 5000 individuals challenged this exclusive view by showing age-dependently up to >20% NMDAR1-autoantibody seroprevalence with comparable immunoglobulin class and titer distribution across health and disease. The key question therefore is to understand the properties of these autoantibodies, also in healthy carriers, in order to assess secondary complications and possible contributions to neuropsychiatric disease. Here, we believe we provide for human NMDAR1-autoantibodies the first comprehensive analysis of their target epitopes and functionality. We selected sera of representative carriers, healthy or diagnosed with very diverse conditions, that is, schizophrenia, age-related disorders like hypertension and diabetes, or anti-NMDAR encephalitis. We show that all positive sera investigated, regardless of source (ill or healthy donor) and immunoglobulin class, provoked NMDAR1 internalization in human-induced pluripotent stem cell-derived neurons and reduction of glutamate-evoked currents in NR1-1b/NR2A-expressing Xenopus oocytes. They displayed frequently polyclonal/polyspecific epitope recognition in the extracellular or intracellular NMDAR1 domains and some additionally in NR2A. We conclude that all circulating NMDAR1-autoantibodies have pathogenic potential regarding the whole spectrum of neuronal NMDAR-mediated effects upon access to the brain in situations of increased blood-brain-barrier permeability.

Class switch DNA recombination (CSR) of the immunoglobulin heavy chain (IgH) locus crucially diversifies antibody biological effector functions. CSR involves the induction of activation-induced cytidine deaminase (AID) expression and AID targeting to switch (S) regions by 14-3-3 adaptors. 14-3-3 adaptors specifically bind to 5'-AGCT-3' repeats, which make up for the core of all IgH locus S regions. They selectively target the upstream and downstream S regions that are set to undergo S-S DNA recombination. We hypothesized that 14-3-3 adaptors function as scaffolds to stabilize CSR enzymatic elements on S regions. Here we demonstrate that all seven 14-3-3β, 14-3-3ε, 14-3-3γ, 14-3-3η, 14-3-3σ, 14-3-3τ and 14-3-3ζ adaptors directly interacted with AID, PKA-Cα (catalytic subunit) and PKA-RIα (regulatory inhibitory subunit) and uracil DNA glycosylase (Ung). 14-3-3 adaptors, however, did not interact with AID C-terminal truncation mutant AIDΔ(180-198) or AIDF193A and AIDL196A point-mutants (which have been shown not to bind to S region DNA and fail to mediate CSR). 14-3-3 adaptors colocalized with AID and replication protein A (RPA) in B cells undergoing CSR. 14-3-3 and AID binding to S region DNA was disrupted by viral protein R (Vpr), an accessory protein of human immunodeficiency virus type-1 (HIV-1), which inhibited CSR without altering AID expression or germline IH-CH transcription. Accordingly, we demonstrated that 14-3-3 directly interact with Vpr, which in turn, also interact with AID, PKA-Cα and Ung. Altogether, our findings suggest that 14-3-3 adaptors play important scaffold functions and nucleate the assembly of multiple CSR factors on S regions. They also show that such assembly can be disrupted by a viral protein, thereby allowing us to hypothesize that small molecule compounds that specifically block 14-3-3 interactions with AID, PKA and/or Ung can be used to inhibit unwanted CSR.

This viewpoint review provides an integrative picture of seemingly contradictory work published on N-methyl-d-aspartate receptor 1 (NMDAR1) autoantibodies (AB). Based on the present state of knowledge, it gives recommendations for the clinical decision process regarding immunosuppressive treatment. Brain antigen-directed AB in general and NMDAR1-AB in particular belong to a preexisting autoimmune repertoire of mammals including humans. Specific autoimmune reactive B cells may get repeatedly (perhaps transiently) boosted by various potential stimulants (e.g., microbiome, infections, or neoplasms) plus less efficiently suppressed over lifespan (gradual loss of tolerance), likely explaining the increasing seroprevalence upon aging (>20% NMDAR1-AB in 80-year-old humans). Pathophysiological significance emerges (I) when AB-specific plasma cells settle in the brain and produce large amounts of brain antigen-directed AB intrathecally and/or (II) in conditions of compromised blood–brain barrier (BBB), for instance, upon injury, infection, inflammation, or genetic predisposition (APOE4 haplotype), which then allows substantial access of circulating AB to the brain. Regarding NMDAR1-AB, functional effects on neurons in vitro and elicitation of brain symptoms in vivo have been demonstrated for immunoglobulin (Ig) classes, IgM, IgA, and IgG. Under conditions of brain inflammation, intrathecal production and class switch to IgG may provoke high NMDAR1-AB (and other brain antigen-directed AB) levels in cerebrospinal fluid (CSF) and serum, causing the severe syndrome named “anti-NMDAR encephalitis,” which then requires immunosuppressive therapy on top of the causal encephalitis treatment (if available). However, negative CSF NMDAR1-AB results cannot exclude chronic effects of serum NMDAR1-AB on the central nervous system, since the brain acts as “immunoprecipitator,” particularly in situations of compromised BBB. In any case of suspected symptomatic consequences of circulating AB directed against brain antigens, leakiness of the BBB should be evaluated by CSF analysis (albumin quotient as proxy) and magnetic resonance imaging before considering immunosuppression.

Purpose The efficacy of bovine immune colostral (colostral) antibodies against verotoxin (VT) 2, flagellum and somatic cells of Escherichia coli ( E. coli ) O157:H7 in mice was determined. Methods Three major immunoglobulin (Ig) classes were isolated from the colostral antibody against VT2 by affinity chromatography and were used for estimation. Mice inoculated with VT2 were administered each Ig class from the colostral antibody, colostral antibody (colostral whey containing antibody) or serum antibody against VT2 at 1 hour after VT2 inoculation. Results All control mice (20/20) died after administration of sterilized saline instead of the colostral antibody. The survival rate was 93.3% (14/15) after administration of S-IgA or IgM antibody, or colostral antibody. Survival rates for IgG antibody and serum antibody administration were 80% (12/15) and 60% (9/15), respectively. Serum concentrations of VT2, which was absorbed from the small intestine in mice after administration of VT2 and colostral antibody, were measured by fluorescence enzyme immunoassay (FEIA). Serum concentrations of VT2 after administration of colostral antibody were lower than those after administration of sterilized saline. Mice inoculated with VT2-producing E. coli 157:H7 were administered anti-flagellum or anti-somatic colostral antibodies. Survival rates for E. coli O157:H7-infected mice administered the anti-flagellum and anti-somatic colostral antibodies were 52.4% (11/21) and 22.2% (4/18), respectively. Furthermore, survival rates increased to 89.5% (17/19) with combined administration of anti-flagellum and anti-VT2 colostral antibodies. Conclusion These results suggest that colostral antibodies against VT2, flagellum and somatic cells are effective against E. coli O157:H7 infection.

Using a reliable and strong reacting antiserum of the rare anti-Cob specificity, it was shown that the Cob antigen was fully developed at birth. Gene dosage effect could not be demonstrated. The frequency of Co(b+) persons in the Danish population (7.8%) was found not to differ from other Caucasian populations. The antibody belonged to immunoglobulin class IgG without ability of fixing complement in vitro.

Sixteen patients with solitary plasmacytomas of bone (SPB) have been reviewed with regard to prognosis, response to treatment, and protein findings. Three patients developed multiple myeloma (MM), and 2 of the patients died due to dissemination. Local recurrence was not seen. Moreover, this study confirms other reports as for the good prognosis of SPB. Intracytoplasmatic immunoglobulin (Ig) has been characterized in tumour tissue from 10 cases by the peroxidase-anti-peroxidase (PAP) method. The tumour tissue stained positively with monoclonal Ig in 8 out of 10 cases. The distribution of myeloma proteins did not differ from that reported in MM. Furthermore, there was complete concordance between immunoglobulin class of paraprotein and intracytoplasmatic Ig.

The immunoglobulin class of circulating immune complexes (IC) was examined in 35 patients with Behçet's syndrome (BS) according to the HLA phenotype of these patients. Cold precipitable complexes were separated and assayed by laser nephelometry and polyethylene glycol precipitable complexes were assayed by rocker immuno-electrophoresis for IgG, IgA and C3. The results suggest that in patients with BS, HLA-B12 is associated with an increased proportion of IgG and a decreased proportion of IgA and C3 in their immune complexes, whilst the converse was found with HLA-B5 or DRw2. The ratio of IgA:IgG in immune complexes was therefore low in patients with HLA-B12 but high in those with HLA-B5 or DRw2. We suggest that a linkage may exist between HLA and gene(s) determining the immunoglobulin class, in response to antigenic stimulation or the site of antigen localization.

R-loops have been described in vivo at the immunoglobulin class switch sequences and at prokaryotic and mitochondrial origins of replication. However, the biochemical mechanism and determinants of R-loop formation are unclear. We find that R-loop formation is nearly eliminated when RNase T1 is added during transcription but not when it is added afterward. Hence, rather than forming simply as an extension of the RNA-DNA hybrid of normal transcription, the RNA must exit the RNA polymerase and compete with the nontemplate DNA strand for an R-loop to form. R-loops persist even when transcription is done in Li+ or Cs+, which do not support G-quartet formation. Hence, R-loop formation does not rely on G-quartet formation. R-loop formation efficiency decreases as the number of switch repeats is decreased, although a very low level of R-loop formation occurs at even one 49-bp switch repeat. R-loop formation decreases sharply as G clustering is reduced, even when G density is kept constant. The critical level for R-loop formation is approximately the same point to which evolution drove the G clustering and G density on the nontemplate strand of mammalian switch regions. This provides an independent basis for concluding that the primary function of G clustering, in the context of high G density, is R-loop formation.

Background Heavy/light chain assay allows the characterization and quantification of immunoglobulin light chains bound to heavy chains for each Ig’k and Ig’λ immunoglobulin class, discriminating between the involved/uninvolved isotypes in plasma cell dyscrasia. The Ig’k/Ig’λ ratio (heavy/light chain ratio) enables to monitor the trend of monoclonal component during therapy and disease evolution. Objective In this study, we evaluate the impact of the heavy/light chain assay in monitoring multiple myeloma patients in comparison with conventional techniques. Methods Serum samples of 28 patients with IgG or IgA monoclonal component were collected for a mean of 109 days and analyzed. The heavy/light chain assay was compared with classical immunoglobulin quantification (Ig’Tot), serum immunofixation electrophoresis, serum protein electrophoresis, and serum-free light chains quantification. Serum samples from 30 healthy patients were used as control (polyclonal). Results Heavy/light chain ratio and serum immunofixation electrophoresis were comparable in 86% of the cases, and free light chain ratio and heavy/light chain ratio in 71.8%. Heavy/light chain assay and Ig’Tot measurements showed a concentration-dependent agreement in monoclonal patients. The heavy/light chain assay was able to quantify the monoclonal component migrating in SPE β region: this occurred in 10% of our IgG and 50% of our IgA patients. Conclusions The concordance scores indicate that heavy/light chain and Ig’Tot assays show differences at high monoclonal component values. The heavy/light chain ratio, serum immunofixation electrophoresis, and free light chain ratio showed partial concordance. Our study confirmed that, in the context of heavy/light chain assay, heavy/light chain Ig’k and Ig’λ absolute values and heavy/light chain ratio are both important tools to monitor the presence of monoclonal component that are difficult to be identified in SPE.

HLAクラスI抗体が血小板輸血不応状態 (platelet transfusion refractoriness: PTR) に関与することについては数多くの報告があるが, IgM型のHLAクラスI抗体 (IgM-HLA抗体) のPTRへの関与についての報告はほとんどない. そこで, PTR患者121人の凍結保存血清のHLA抗体スクリーニングを, 磁性粒子を用いた Mixed passive hemagglutination assay (M-MPHA) 法, Flow cytometric reagents for detection of panel-reactive antibody against HLA Class I antigens (FlowPRA) 法, Anti-human immunoglobulin lymphocyte cytotoxity test (AHG-LCT) 法により行い, IgM-HLA抗体のPTRへの関与については, 輸血24時間後の補正血小板増加数 (CCI24hours) による血小板輸血効果から推測した. その結果, M-MPHA法により121症例中48症例からIgM-HLA抗体が検出された. 一方, FlowPRA法により検出できたIgM-HLA抗体は, それら48例中35例, AHG-LCT法では20例のみであった. 血小板輸血効果は, IgM-HLA抗体を保有する, 48症例中7症例74輸血において判定できた. IgM-HLA抗体の特異性に対応する抗原を持たない輸血では, CCI24hoursが19.7±4.7(×109/L) を示し輸血効果を得ることができたが, 対応する抗原を持つ輸血では, CCI24hoursが2.0±19(×109/L) を示し輸血効果を得られなかった. PTR患者に高頻度に存在するIgM-HLA抗体は, PTRの原因になると考えられ, その半数以上はAHG-LCT法により検出できなかった. M-MPHAをHLA抗体スクリーニング, 血小板輸血の際の交差試験に用いることで, PTR症例の原因解析と輸血効果の向上に貢献できる可能性がある.