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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.

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.

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.

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.

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.

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.

Hyper-IgM immunodeficiency (HIM) is an immunological disorder characterized by normal or elevated serum IgM levels, and reduced serum IgG and IgA levels, due to the disruption of immunoglobulin class switching in B cells. X-linked hyper-IgM is caused by the defective expression of the CD40 ligand on activated T cells, which induces immunoglobulin class switching along with some cytokines, such as interleukin 4, by the signal transduction of CD40 in B cells. We report on a Japanese girl who initially showed low serum IgM, IgG and IgA levels like patients with common variable immunodeficiency; however, in the course of time, serum IgG levels became reduced and serum IgM levels increased, resulting in the typical immunoglobulin profile of HIM. Neutropenia, one of the features of X-linked HIM, was not observed. In spite of extremely low serum IgG levels, she did not show any predisposition to severe infection, even without gammaglobulin replacement therapy. No mutation of the CD40 ligand or CD40 was detected. Sequencing of the complementarity-determining region of immunoglobulin heavy-chain genes in peripheral B lymphocytes revealed that they were all in frame, and insertion of the N region was detected. These results indicate that the heavy-chain gene rearrangement in the patient’s B cells is intact. Non-X-linked HIM has heterogeneous pathogenetic mechanisms, and some groups may show the resistance to infection at the healthy donor level. The underlying defects in non-X-linked HIM might be specifically involved in class switching.

Background The principle of the erythrocyte sedimentation rate (ESR) as assessed by TEST 1 is different from that of Westergren-based methods. This could result in different influences on the tests by paraproteins. Methods We investigated the effect of paraproteins on ESR readings by TEST 1 ( y) and the StarrSed ( x), a Westergren-based method, in 142 patients with paraproteinaemia. Agreement (Passing-Bablok) and bias (Bland–Altman) between methods was investigated and compared with that of a control population. Results A poor agreement between the two methods was found in patients with a paraprotein ( y = 0.67 x + 3.3) in comparison with that of the control population ( y = 0.96 x + 0.2). Large differences between methods were present when ESR readings were >40 mm/hour, but clinical interpretation was similar in 90% of cases. Linear regression showed a concentration dependent influence of paraproteins on ESR readings by the StarrSed, especially for immunoglobulin class IgM. Conclusion ESR readings by TEST 1 result in similar clinical interpretation for most subjects, but readings are less influenced by the presence of a paraprotein than those of a Westergren-based method.

Patients with the antiphospholipid syndrome (APS) have autoantibodies directed against epitopes on β(2) glycoprotein I (β(2)GPI). We describe herein the performance characteristics of standardized enzyme‐linked immunosorbent assays (ELISAs) for anti‐β(2)GPI of the three major immunoglobulin classes: IgG, IgA, and IgM. All three assays generated highly linear standard curves (5 points, r ≥ 0.993 for each); precision was excellent both intra‐assay and run‐to‐run, with coefficients of variation (CV) ranging from 2.3% to 6.6%. Values for IgG anti‐β(2)GPI correlated strongly with those obtained by an earlier method (r = 0.80, P < 0.0001). A study group consisting of 203 healthy subjects was used to generate percentile‐based reference intervals for all three classes of anti‐β(2)GPI. APS subjects' anti‐β(2)GPI were found to differ significantly (P < 0.0001 for each) for those of the control population. All three assays correlated well with β(2)GPI‐dependent anticardiolipin antibody (aCL) measurements; IgG: r = 0.94 (P < 0.0001), for IgA: r = 0.82 (P < 0.001) and for IgM: r = 0.84 (P < 0.0001). We suggest that these ELISAs may provide valuable standardized measurements of IgG, IgA, and IgM anti‐β(2)GPI. J. Clin. Lab. Ana. 12:293–297, 1998. © 1998 Wiley‐Liss, Inc.

The state of the art in routine CSF analysis is reviewed with particular reference to multiple sclerosis regarding: (1) The physiology and pathophysiology of blood-CSF barrier function and dysfunction with the CSF flow rate as main modulator of blood- and brain-derived protein concentrations in CSF; (2) The neuroimmunological aspects regarding (a) patterns of disease-related immunoglobulin class response (IgG, lgA, IgM) in actual Reiber graphs with reference to specific parameters and optional tests, and (b) the oligoclonal, polyspecific antibody synthesis in brain; (3) Particular marker proteins in CSF and blood for differential diagnosis of neurological diseases; (4) Mathematical base for evaluations of CSF data with an example of a multiple sclerosis patient for calculation of intrathecal immunoglobulin and antibody synthesis as well as Antibody Index.

Current textbooks for transfusion medicine state that anti-A and/or anti-B (anti-A/B) agglutination titers--and thus the respective antibody concentrations--reach their maximum in individuals 5 to 10 years old and then gradually decline with the increasing age of the individual. This statement is largely based on a study by Thomsen and Kettel that dates to 1929. In the present article, ABO antibodies in sera of 175 healthy persons aged 61 to 97 years, as well as sera of 170 newborn infants and children aged 0 to 17 years, were analyzed. Microhemagglutination tests were performed with all sera and complemented by ABO enzyme-linked immunosorbent assays to measure the immunoglobulin class (IgM, IgG, and IgA) of the anti-A/B. As in a previous study using sera of persons aged 20 to 67 years, individual differences exceeded age-related changes for all variables. Median values of IgG and IgA anti-A/B were elevated in elderly persons of blood group O, whereas no significant changes were observed in other variables. In particular, the decrease in agglutination titers with the increasing age of the individuals was far less pronounced than previously described; even in sera of persons aged 90 to 97 years, median agglutination titers of 128 were found. Results in the sera of children confirm previously reported data that agglutination titers and IgM anti-A/B reached adult levels at the age of 5 to 10 years.

Plasma exchange with a rotating filter. We have modified a rotating filter system to provide therapeutic plasma exchange. Seventeen patients underwent 188 treatments. Blood flows to the filter ranged from 75 to 100 ml/min; mean filtration fraction was 64 ± 1% (± SE, N = 188). Mean plasma removal rate per treatment was 40.2 ± 0.6 ml/min; net plasma removed per treatment was 3231 ± 53ml (N = 188); mean treatment time was 83 ± 2 minutes (N = 188). Mean percent decline in platelet count was 15 ± 4% (N = 46). Immunoglobulin kinetics were evaluated in order to validate our method of treatment prescription. The apparent volume of distribution (AVD) for each immunoglobulin class was compared to our estimate for plasma volume (EPV). The fraction AVD/EPV for IgG was 0.97 ± 0.04 (N = 14), for IgA was 0.87 ± 0.04 (N = 13) and for IgM was 0.96 ± 0.3 (N = 26). Use of the EPV allowed for accurate prediction of treatment results. Correlation between expected and actual decline in serum levels revealed an r value of 0.86 for IgG (P = 0.0002), 0.88 for IgA (P = 0.0001), and 0.57 for IgM (P < 0.003). We conclude that a rotating filter system can provide a highly efficient means of plasma exchange. The use of a simplified method of estimating plasma volume allows for a reliable prediction of treatment results.

The presence of IgG and IgA on motile spermatozoa from normal semen donors and men from infertile couples was studied with mixed antiglobulin reaction (MAR) tests. The percentage of motile spermatozoa with IgG (IgG MAR%) was found to be related to the circulating antispermatozoal IgG. No direct relation could be detected between the IgG MAR% and the sperm agglutinating activity in seminal plasma (SP) or the percentage of motile spermatozoa showing the shaking phenomenon (S%) in the sperm cervical mucus contact (SCMC) test. The percentage of motile spermatozoa with IgA (IgA MAR%) showed no direct relation to the sperm agglutinating activity in serum and SP, but was roughly proportional with the S%. It was discerned that the shaking phenomenon in the SCMC test was probably due to presence of IgA on the motile spermatozoa. Previously it had been demonstrated that also the sperm agglutinating activity in SP is caused by IgA that is probably locally produced in the male genital tract. In conclusion it was thought that the reduced ability of penetration into cervical mucus by spermatozoa from infertile men is caused by locally produced IgA.

Cold-reactive lymphocytotoxic antibodies are present in the serum of most patients with systemic lupus erythematosus (SLE) (Mittal et al., 1970; Terasaki et al., 1970). They appear to be equally cytotoxic for autologous and heterologous lymphocytes (Stastny and Ziff, 1971). Studies of the nature of these antibodies showed that their cytotoxic effect is temperature-dependent and maximal at 15°C, that their immunoglobulin class is IgM, and that they are equally reactive with T and B lymphocytes (Winfield et al., 1975a). Studies of the clinical significance of cold-reactive lymphocytotoxic antibodies in SLE have shown a consistent association with neuropsychiatric complications (Butler et al., 1972; Bluestein and Zvaifier, 1976; Bresnihan et al., 1977b). In other respects, however, clinical studies have been inconclusive, which may partly be related to the retrospective nature of most series. Previous studies have suggested an association between cold-reactive lymphocytotoxic antibodies and lymphopenia (Winfield et al., 1975b; Utsinger, 1976). A detailed prospective clinical analysis of SLE began at Hammersmith Hospital in 1973. In all, 50 patients have been investigated, and their clinical features have been described elsewhere (Grigor et al., 1978). This report relates the clinical features in these patients to the presence of lymphocytotoxic antibodies.

There is no doubt that the interpretation of a positive lymphocytotoxic crossmatch test has changed over the past 10-15 years. It is now generally accepted that the original dogma put forward in the mid-1960s "that a renal transplant must not be performed in the presence of a positive lymphocytotoxic crossmatch" is no longer tenable, and many positive crossmatch transplants have already been successfully carried out. However, the precise conditions under which such a transplant can be performed are still not fully understood. Some factors which should be considered when deciding whether or not to transplant in the presence of a positive crossmatch are: (1) the specificity of the antibody, and this can be HLA class I, class II or non-HLA; (2) the time interval between the last positive crossmatch serum and transplantation; and (3) the immunoglobulin class of the antibody, either IgG or IgM.

The immunoglobulin classes of platelet alloantibodies were studied using monospecific antisera in a radiolabeled technique. 14 of 28 consecutively studied multiply transfused oncology patients demonstrated platelet antibodies. These 14 patients were also refractory to random donor platelets. The immunoglobulin classes of these platelet antibodies were found to be: IgG alone 4, IgM alone 4, IgG and IgM 5, IgM plus IgA 1. The results in this study suggest that using monospecific antisera other than anti-IgG alone, one can detect additional antibodies involved in the immune destruction of platelets.

Immunoglobulin-specific assays are currently available for detection of patients with antibody-mediated infertility. Care must be taken in insuring that the correct immunoglobulin class is assayed, the assay is directed to the possible interaction of antibodies and sperm in the male or female genital tract, and the antigen employed will not detect antibodies against antigens not found on the plasma membrane of living sperm.

Antibodies against the cytoplasm of normal human epidermal cells were found in both a newborn baby with incontinentia pigmenti and in her normal mother. These antibodies showed no tissue or species specificity as in the case of anti-nuclear antibodies in SLE. The antibodies were assayed by indirect immunofluorescence. The antibody titer in the serum of the baby gradually decreased over a period of months while the mother's titer remained high. The generalized vesiculo-bullous eruption noted at birth subsided with the decrease of antibody titer. The immunoglobulin class of the antibodies was determined to be IgG, which passes through the placental barrier. It is suggested that the anti-cytoplasmic antibodies produced by some unknown cause in pregnant women could be transferred to the baby and induce a variety of disorders.

A new test to determine the immunoglobulin class of erythrocyte antibodies is presented. Dithiothreitol (DTT), at a concentration of 0.01 m, has been used in a rapid 15 min, 37°C incubation test system. Dialysis is not required. The accuracy of this new DTT test was compared to a standard 2-ME procedure. Human sera containing saline-acting and incomplete varieties of erythrocyte antibodies were tested. Identical results were obtained by both methods with 292 of 302 (96.7%) test sera. Anion-exchange chromatography was employed to produce erythrocyte antibody solutions of known immunoglobulin class. Incubation of these solutions with DTT decreased the immunologic reactivity of IgM erythrocyte antibodies, without affecting the activity of IgG varieties.

Paired serum specimens from 149 patients with six different infections verified by a significant rise in the specific antibody level were tested for anticardiolipin antibodies using enzyme-linked immunosorbent assay. Significantly raised levels, at least in one immunoglobulin class, were detected in 32% of the cases, and significant changes in the level indicating an ongoing process, in 26%. Taken as a whole, the response involved the immunoglobulins IgG, IgM, and IgA, although in patients with mumps the significantly raised levels were virtually confined to the IgA class. The binding of syphilitic antibodies to solid-phase cardiolipin was readily inhibited by cardiolipin liposomes, whereas this pattern of reactivity was noted in only one of four nonsyphilitic sera. It was concluded that anticardiolipin antibodies occur very frequently in a wide variety of uncomplicated infections.

Summary(1) By techniques of radioimmunoelectrophoresis and radioimmunodiffusion using radioactive poliovirus, it was shown that the quantity of poliovirus antibodies in a serum and the immunoglobulin class of these antibodies can be determined. (2) By these techniques it was shown that adult human serum contains A Immunoglobulin (IgA) poliovirus antibodies as well as G Immunoglobulin (IgG) polio antibodies. (3) Some sera contain a higher concentration of A Immunoglobulin (IgA) polio antibodies than G Immunoglobulin (IgG) polio antibodies.

The immunoglobulins G, A, M, and D were determined in three series of Ethiopian preschool children. The levels of IgG and IgD were significantly higher than those found in a group of Swedish children of the same age; the mean levels of IgD being five to six times higher than in the Swedish series. The concentrations of the new immunoglobulin class, IgE, were also studied. The levels of IgE were between sixteen and twenty times higher than in Swedish children, and in a group with verified infection with Ascaris lumbricoides the level was twenty-eight times higher. These findings favour the hypothesis that parasitic infestations are important factors in stimulating IgE production.

THE presence of antibodies that react with nuclei in the serums of patients with systemic lupus erythematosus is well established. Human antibodies have been found to belong to 1 of 3 classes of immunoglobulins that can be distinguished from each other by antigenic differences in the heavy polypeptide chains. These are the IgG, the IgA and the IgM globulins. The immunoglobulin class to which the antinuclear factor belongs has previously been investigated in small numbers of patients. Goodman and Fahey1 first demonstrated the presence of both IgG and IgM antinuclear factors, and recent work by Barnett and his co-workers2 and . . .

Allergic rhinitis is among the atopic allergic diseases. Sera from patients with atopic disease possess reaginic antibodies that are positive Prausnitz-Kiistner reaction substances. Recently, a new immunoglobulin class — IgE — was discovered, in which the reaginic antibodies are present in high concentration. The chemical structure and biologic properties of this new immunoglobulin are described, and further investigative efforts for IgE were proposed to clarify the defense mechanism of IgE.

Indirect hemagglutination studies were performed on 10 incomplete anti-Rh sera from mothers after incompatible pregnancies, on 19 incomplete anti-Rh plasma samples from preimmunized and repeatedly boosted individuals and on 3 anti-Rh plasma pools. Group O Rh-positive red blood cells were agglutinated by antisera to immunoglobulins. Anti-Rh antibodies after incompatible pregnancies were found to belong to the immunoglobulin class IgG and to the subclasses IgG1, IgG3 and IgG4 only. In most anti-Rh samples from preimmunized and repeatedly boosted subjects, IgG and IgA were present. In six anti-Rh samples of this group, the subclass IgG2 could be demonstrated.

An indirect fluorescent-antibody technique was developed for detection of antibodies to Neisseria gonorrhoeae in sera from patients with uncomplicated gonorrhea. The test antigen is a strain of N. gonorrhoeae selected for its stability in the laboratory and for its reactivity with sera from culturally positive females. A 1:16 dilution of sera obviated the reactivities associated with natural antibodies in normal sera. The specificities, strengths, and degree of fluorescence of the conjugate were defined to establish data for comparison with other polyvalent reagents and to minimize preferential recognition of any one immunoglobulin class. Seventy-nine percent of sera from culturally positive females were reactive; only 4% of sera from culturally negative females reacted in the test. Reproducibility was 94% as judged by duplicate examination of 340 coded sera. The discrepant pairs (6%) were read as either 1+ or 2+ fluorescence. Only 15% of the 340 sera were in the borderline (1+, 2+) area where judgment of fluorescence is most critical.

Summary 1. Reduced levels of serum immunoglobulins have been found in association with a variety of diseases of the gastrointestinal tract. 2. Immunoglobulin reductions may involve all three major immunoglobulin classes or be restricted to one or more immunoglobulin class. 3. IgA, which is intimately associated with the gastrointestinal tract in a variety of ways, is the immunoglobulin most commonly deficient. 4. In most instances precise knowledge is lacking to explain the relationships between reduced immunoglobulin levels and gastrointestinal disease. 5. Detection of reduced immunoglobulin levels may provide early signal evidence of unrecognized gastrointestinal disease.

Low-ionic-strength solution (LISS) reagents and methodologies have become popular in recent years in hospital transfusion service laboratories for alloantibody detection and compatibility testing of blood recipients. It has been the experience with all other hemagglutination technics that some examples of alloantibodies unpredictably fail to react. Such is the case with this patient's alloantibody with respect to LISS. The patient had a significant hemolytic transfusion reaction due to Kell incompatibility of one unit of packed human erythrocytes. Using various LISS reagents and methodologies, the anti-Kell was undetectable in pretransfusion and posttransfusion samples through the fifth day. The anti-Kell was of immunoglobulin class IgG, and it was detected in saline solution or albumin at room temperature, at 37 C and by the antiglobulin technic.

Serum was obtained from a woman with a high (greater than 1000) titre of antispermatozoal antibody of IgA immunoglobulin class determined by the indirect immunobead test (IBT). It was found that the serum could sensitize normal sperm to give a strong shaking reaction in the semen-cervical mucus contact test (SCMCT). The capacity to induce shaking was retained after absorption of the serum with protein A-sepharose, but lost after absorption with rabbit antihuman IgA. The results therefore suggest that antispermatozoal antibodies of IgA class from serum can induce shaking, and are consistent with the possibility that the Fc fragment (rather than secretory component or J-chain) may be important for induction of shaking in the conventional SCMCT.

Significantly raised serum levels of a new Summary class of immunoglobulins, provisionally called IgND, were found in 63% of patients with allergic asthma compared to 5% of patients with non-allergic asthma. Mean concentration of IgND was 6 times higher in the group with allergic asthma than in the group with non-allergic asthma. These findings are of particular interest since IgND has many characteristics in common with reagins. No differences were found between allergic and non-allergic patients with respect to the concentration of the immunoglobulins A, D, G, or M in the serum.

Gel-diffusion and the enzyme-linked immunosorbent assay (ELISA) were used to quantify and to identify the immunoglobulin class of teichoic acid antibodies in patients with chronic staphylococcal osteomyelitis and a wide variety of other infections. Teichoic acid antibodies were identified by gel-diffusion in 14 of 23 patients with staphylococcal endocarditis, six of 30 with staphylococcal bacteremia without endocarditis, four of 35 with staphylococcal skeletal infections, and one of 45 with nonstaphylococcal infections. None of the 20 patients with chronic staphylococcal osteomyelitis had positive gel-diffusion assays, even though many had had their infections for several years. The ELISA method was more sensitive than gel-diffusion in measuring teichoic acid antibodies, but was also much less specific. Teichoic acid antibodies were detected predominantly in the IgG fraction of serum. Our findings suggest that the presence and degree of antigenemia are more important than the duration of the staphylococcal infection in stimulating production of teichoic acid antibodies.

In order to improve the efficiency of IBT screening of sera for sperm antibodies, the use of immunobeads with attached rabbit antibodies directed against whole human immunoglobulin (IBT-GAM) was investigated and compared with the use of separate immunobeads specific for each of the main immunoglobulin classes (IBT-IgG, IBT-IgA, IBT-IgM). Sera found positive by the IBT-GAM procedure were then tested by IBT-IgG, -IgA, and -IgM procedures to determine the immunoglobulin class or classes of the sperm antibody. The new procedure is much more efficient for screening larger batches of sera and gives results identical with those from the old procedure when greater than or equal to 50% sperm coating is used as criterion of positivity. We now use the IBT-GAM procedure for initial screening of all sera, followed by further testing of positive sera on the same preparation to determine the immunoglobulin class or classes of the antibody.

Sera from 214 infertile patients were assayed for antisperm antibodies using the IBT, GAT, and SIT. The new IBT methodology was compared with the more classical tests. Although SIT and GAT did not correlate to any particular antibody class, both were negative if IgA was present alone. The immunoglobulin class presented a preferential sperm region binding site: IgG to the head and tail, IgM to tail tip only, IgA to head and tail. Furthermore, these immunoglobulins from the serum of male patients bound differently to sperm than immunoglobulins from female serum. Finally, we were able to calculate the relative sensitivity, specificity, and predictive values for these tests.

The immunoglobulin class of rheumatoid factor (RF) in sera and synovial fluids of patients with rheumatic diseases was measured by a solid-phase enzyme immunoassay. IgG-RF was frequently found in seronegative sera as well as in seropositive sera of rheumatic patients. Titers of IgG-RF were higher in the active phase than in the inactive phase of SLE and showed a correlation to the levels of hypocomplementemia and circulating immune complexes in SLE sera. Titers of IgA-RF were likewise higher in the active-phase of SLE with a correlation to titers of circulating immune complexes. IgA-RF was also found frequently in sera of patients with Sjogren's syndrome.

Prelude There are two types of disulfide bridges in immunoglobulins. One is the conserved intrachain bridge, spanning about 60 to 70 amino acid residues and found, as a monotonous theme, in every immunoglobulin domain. Buried deep between the opposing ~3-sheets, these bridges are shielded from solvent and, ordinarily, can be reduced only in the presence of denaturing agents. In contrast, the remaining disulfide bridges- interchain as well as occasional extra intrachain bonds- form a set of variations, differing in number and location according to immunoglobulin class and species, apparently constrained only by the necessity of conforming to the overall structure of the immunoglobulin fold. The latter bridges are typically located on the surface of the molecule, external to the ~3-sheets; they are accessible to solvent and are usually relatively easily reduced. Although their presence may impart special properties to certain immunoglobulin classes, the interchain disulfide bridges are not required for chain association, noncovalent forces generally being adequate for this task (see reviews by Beale & Feinstein, 1976, and Amzel & Poljak, 1979). The presence of buried conserved and superficial nonconserved disulfide bridges is also a characteristic feature of other extracellular proteins (Thornton, 1981). In historical context, recognition of the existence (Edelman, 1959; Edelman & Poulik, 1961), number and location (Nisonoff et al., 1961; Palmer and Nisonoff, 1964), and lability to reduction (Porter, 1962; Fleischman et al., 1963) of the interchain bridges in immunoglobulins played a crucial role in the establishment of the familiar four-chain model. In this article, I shall discuss some of the work carried out in my laboratory that bears on the general subject of the disulfide bridges in immunoglobulins. Partly by design, but mostly by accident, investigations of disulfide bridges have recurred in my research from the time I was a medical student at Yale, working in the laboratory of Fred Richards on the reduction and reoxidation of the disulfide bonds of ribonuclease (Steiner, t959). In the Porter laboratory, I studied patterns of interchain disulfide bonds in rabbit and human IgG. When I came to MIT, I drew on these experiences to work out a method for preparing heavy-atom derivatives of immunoglobulins in which mercuric ions are inserted into the interchain disulfide bridges. This was followed by the investigation of a crystallizable immunoglobulin strangely deficient in interchain bonds. Very recently, we have found that the light chains of bullfrog immunoglobulins have apparently replaced their bridge to the heavy

The aim of this study was to determine the immunoglobulin class of circulating antisperm antibody using a technique called the indirect immunobead test (IBT). In the IBT sperm bound antibodies are detected using polyacrylamide beads coated with rabbit antihuman immunoglobulin classes IgG, IgA, and IgM. Of the 20 infertile men with serum immobilizins, 100% were found to be positive for sperm-bound IgG, 50% positive for IgA, and 0% positive for IgM, using the IBT. Similarly, 20 infertile females with serum immobilizins showed 95% positivity for IgG, 60% for IgA, and 15% for IgM. Thus there was a good correspondence between the presence of serum immobilizins as determined by the sperm immobilization test (SIT) and the IBT. This study provides data that indicates that IgG and IgA are the two major immunoglobulin classes of sperm antibody in male and female immune sera as detected by a simple, sensitive immunological technique, the serum IBT.

Nineteen patients with a variety of well-defined primary immunodeficiency diseases were examined for ocular abnormalities. Eight patients with low levels, or absence, of all the major serum immunoglobulins had conjunctivitis or keratoconjunctivitis associated with bacterial infection. The remaining 11 patients, who had at least one immunoglobulin class present in normal concentration in the serum, showed no inflammatory ocular lesion. Absence of only IgA, the major tear immunoglobulin, did not predispose the eye to these lesions.

Four patients with nonhematologic malignancies had the simultaneous finding of hemolytic anemia due to high-titer cold agglutinins. In each patient, the cold agglutinin had "anti-I" specificity and was of the IgM kappa immunoglobulin class. Although patients with hematologic malignancies not uncommonly have cold agglutinins, the association between these antibodies and nonhematologic malignancies is unusual.

Anti-Rd (Radin) was first described in association with five cases of hemolytic disease of the newborn. The authors report an anti-Rd that was demonstrated following the transfusion of a Radin positive unit of blood. The antibody appears to be of the IgC immunoglobulin class and increased in titer following the transfusion.

Antilymphocyte antibody (ALA) in systemic lupus erythematosus (SLE) was studied using an indirect immunofluorescent technique with air-dried, acetone-fixed lymphocytes. Ninety-four per cent of patients with SLE and 65 per cent of their relatives had ALA. The ALA response in SLE patients involved antibodies of all classes. However, the ALA in their relatives was primarily of the IgM class. Restriction of the class of ALA in asymptomatic relatives is analogous to that seen with anti-RNA antibodies and suggests that the switch to production of autoantibodies of the IgG class may be important in the pathogenesis of SLE.

Summary Circulating immune complexes were isolated from 15 patients with acute leukaemia and 13 healthy blood donors by PEG precipitation. These were analysed according to their IgG, IgM and C4 content by optical rate nephelometry. Immune complexes of leukaemic patients contained higher amounts of IgM as compared to those from normal subjects. The clinical relevance of IgM containing immune complexes in leukaemia is discussed.

Agarose gel electrophoresis and immunofixation of CSF and serum from 39 patients with multiple sclerosis (MS) revealed oligoclonal IgG in the CSF in all cases and oligoclonal IgA and IgM in 1 patient each. IgG kappa bands only were found in 10 patients, while no patient had IgG lambda bands alone. IgG kappa bands predominated in 20 patients and IgG lambda bands in 5, while 4 patients had the same number of IgG kappa and IgG lambda bands. Twenty-seven patients also displayed IgG bands with kappa and lambda present simultaneously. Bands of free lambda chains were found in 7 patients, while free kappa chain bands were not seen. One or 2 faint IgG bands in 4 patients constituted the only serum abnormality. In 4 additional MS patients selected on the basis of normal findings on agarose gel electrophoresis of the CSF, immunofixation did not reveal oligoclonal Ig, while isoelectric focusing showed bands in 1. Immunofixation is recommended for proving the presence of oligoclonal Ig in CSF and for characterizing oligoclonal Ig into classes and types of light chains.

Serum immunoglobulin levels were estimated in 19 patients with aplastic anaemia. Although the mean levels for IgG, IgA and IgM for the group as a whole were within the normal range, 8 individual cases showed low levels of one or more immunoglobulin class, suggesting a disturbance in immunoglobulin production. One of these patients had a thymoma, and another positive tests for anti-nuclear factor, but there was no evidence of auto-immune disease in the others. It is suggested that ‘aplastic anaemia’ may sometimes be a disease due to injury of a stem cell subserving both haemopoietic and immunological function.

Fractionation of serum samples from head and neck cancer patients and their assay for agglutination activity toward oral microorganisms showed that the activity was derived from IgG, 7S IgA, 10S (dimeric) IgA, and IgM, with considerable activity in the 10S IgA region. These findings probably account for the lack of a significant relationship among levels of individual serum immunoglobulins, agglutination titers, and caries activity presented in an earlier study. Conversely, most of the agglutinating activity in fractionated saliva was attributed to 11S IgA, presumably secretory IgA, with some activity from a 19S substance and, in the caries-active patients, from a higher molecular weight factor. These data correspond to positive correlations between saliva IgA levels, agglutination titers, and absence of caries in these patients.

The serology of treponemal disease has become simpler and more rational in recent years, mainly as a result of the widespread adoption of specific antibody tests and the use of monospecific fluorescent antibody procedures which give information about the immunoglobulin class of antibodies. A set of tests which has proved particularly useful in routine diagnosis is the following: quantitative TPHA test, quantitative VDRL test, and monospecific (IgG and IgM) FTA-ABS tests. This combination is especially valuable in the assessment of new patients with positive results to serological tests and in the management of patients with treated syphilis.

In order to elucidate the immunological mechanism in the pathogenesis of pityriasis rosea, immunofluorescent studies were performed on sera obtained from forty patients with this disease. Antibodies against the cytoplasm of normal human epidermal cells were demonstrated in the sera of all patients. The antibody titer showed a tendency to increase within 3 weeks after onset of secondary eruptions and then to decrease gradually until the period of recovery. The immunoglobulin class was determined to be IgM. Furthermore, by the direct immunofluorescent technique, deposits of IgM in the epidermal cells of skin lesions were demonstrated in 3 of 6 herald lesions and in 1 of 4 secondary eruptions. It is suggested that anti-cytoplasmic antibodies produced by some unknown cause may induce the development of secondary eruptions of this disease.