IgM Immune Complexes Research Articles

Investigation of the nutritional state of children in a Congolese village. I. Anthropometrical data, plasma prealbumin, albumin, immunoglobulins, ferritin, C-reactive protein, circulating immune complexes.

The nutritional status of an unselected group of 111 children from the village of Bouansa, People's Republic of the Congo, was studied. Comprehensive clinical examinations, anthropometrical measurements and analysis of albumin, prealbumin, ferritin, C-reactive protein (CRP), IgA, IgG, IgM, IgE, IgG- and IgM-circulating immune complexes (CIC) were carried out. The results show, by anthropometrical classification, a high prevalence of moderate malnutrition. Low levels of plasma proteins and high levels of immunoglobulins and CIC were found. No correlation between anthropometrical classification and plasma proteins was established. Children with increased levels of CRP showed low prealbumin values and increased levels of ferritin. Patterns of immunoglobulins and CIC were close to those found in other studies in tropical countries. To evaluate the anthropometrical and biochemical findings it is necessary to take into consideration the apparently healthy appearance of the children, which shows the degree of adaptation to the limited availability of food and the high rate of acute and chronic infections.

On the Interaction of the First Complement Component C1 and its Subunit Clq with Solid‐Phase IgM Immune Complexes

The interaction of C1 and C1q with solid-phase anti-dextran MOPC-104E IgM was studied. An enzyme-linked immunosorbent assay (ELISA) was used to detect bound C1q. The results revealed that immobilized IgM is converted to the functionally active 'staple' conformation by the specific polyvalent ligand dextran (B 1355/S). C1q is fixed to IgM dependent on the antigen concentration, and its binding might be explained by assuming a functional binding constant (K) of approximately 10(9) M-1. Molecules bound with a K in the range of 10(7) M-1 cannot be detected by this ELISA procedure. The fixation of C1q saturated with an excess of the C1r2S2-tetramer differs from that of free C1q. C1q incorporated in the C1 complex rapidly dissociates independently of the antigen concentration. Since the complement binding sites are located at definite positions on the IgM molecule because of its pentameric structure, it is suggested that the distinguishable association properties of C1 and C1q are brought about from the altered flexibility of the C1q molecule complexed with C1r2S2.

Preliminary studies on the detection, isolation and partial characterization of Clq-containing IgM immune complexes in sera of patients with primary biliary cirrhosis

The complement system is activated in primary biliary cirrhosis (PBC) and this activated state may be medicated by immunoreactive IgM. To identify and further characterize the relationship between the complement (Clq) and IgM in PBC sera, we developed an anti-Clq ELISA method which allowed detection of Clq-containing circulating immune-like complexes. Utilizing this technique, sera from 3 out of 5 patients with PBC revealed circulating immune-like complexes. Moreover, when serum samples were specifically examined for the presence of IgM containing Clq complexes, four of four samples examined were positive. Additional experiments indicated that these immune-like complexes could be removed from PBC sera by means of an anti-Clq immunoadsorbent. Upon subsequent isolation and characterization, these immune-like complexes demonstrated polypeptide chains corresponding to both human Clq and human IgM. Our experimental studies establish that Clq-containing IgM-like complexes can occur in the serum of patients with PBC, and provide additional support for the proposal that immunoreactive IgM can contribute to the activated complement system observed in PBC.

Molecular cloning of two CD7 (T-cell leukemia antigen) cDNAs by a COS cell expression system.

The human CD7 antigen (gp40) is a cell surface glycoprotein found on thymocytes and mature T-cells. It is one of the earliest antigens to appear on cells of the T-lymphocyte lineage, and the most reliable clinical marker of T-cell acute lymphocytic leukemia. This report describes the isolation and nucleotide sequence of a full length CD7 cDNA, and of a cDNA for an unusual intron-bearing precursor. The DNA sequence of the clone predicts a highly glycosylated membrane protein with homology to members of the immunoglobulin superfamily, and no relationship to known oncogenes. Over-expression of CD7 RNA was observed in only one T-cell tumor line, and genomic DNA rearrangement was not observed in any lines. Prompted by a recent suggestion that CD7 plays a role in IgM binding, COS cells expressing CD7 were tested and found not to bind IgM or IgM immune complexes.

Characteristics of chemically aggregated IgM in an immunoglobulin class-specific immune complex assay

Immune complexes have been implicated in the pathogenesis of a number of infectious diseases. The predominant immunoglobulin class associated with circulating immune complexes is IgG, although immune complexes containing IgM have been described. The role of IgM immune complexes in disease pathogenesis has been difficult to characterize due to the lack of a reliable in vitro model. Immunoglobulins aggregated with bis-diazotized benzidine (BDB) are known to function as model immune complexes. We have developed an IgM immune complex using BDB-aggregated IgM which can be used as a reference in a conglutinin-based immune complex assay. Using this assay system, humans and chimpanzees with acute hepatitis A were found to have circulating immune complexes that contained IgM as the predominant antibody.

Characterization of circulating Yersinia-specific immune complexes in patients with yersiniosis

The size of immune complexes (ICs) containing Yersinia enterocolitica antigens was studied by size exclusion high-pressure liquid chromatography and sucrose density gradient ultracentrifugation in sera of patients with recent yersiniosis. The ICs detected were relatively small, i.e., of equal size to or slightly larger than the corresponding anti-Yersinia antibodies. The size of the ICs was equal in the patients with Yersinia-triggered reactive arthritis and in those recovering without complications. No changes were observed during a follow-up. The equal size of ICs in the patients with and without arthritis also suggests that antigens and antibodies involved are similar in both patient groups. Taken together with our earlier findings indicating occurrence of high concentrations of Yersinia IgM ICs in the arthritic patients, the present results suggest that Yersinia-IgM ICs have a role in the pathogenesis of Yersinia-triggered reactive arthritis.

Detection of specific circulating antigen, immune complexes and antibodies in human hydatidosis from Turkana (Kenya) and Great Britain, by enzyme-immunoassay.

Circulating antigen, specific immune complexes (IgG and IgM) and specific antibodies (IgG, IgM, IgE and IgA) were detected by enzyme-linked immunosorbent assay (ELISA) in the sera of hydatid (Echinococcus granulosus) patients from Turkana (Kenya) and the UK. Specific IgG and IgM antibodies predominated in current UK hydatid infections, while all classes of specific antibodies were lower in the Turkana patients. Circulating antigen, detected in 3% polyethylene glycol (PEG) precipitated complexes, using peroxidase conjugated hyperimmune human hydatid IgG (Fab) was more specific in ELISA than either antibody or immune complex assays where peroxidase conjugated anti-human IgG was used. Anti-human immunoglobulin ('rheumatoid' factor) was not detected in hydatid sera. Serum antigen, specific IgM immune complexes and specific IgM antibodies were associated with UK cases of current hydatid infection in contrast to patients with previous histories of hydatidosis. In 3 hydatid patients (from UK) levels of circulating antigen and specific IgM immune complexes rapidly declined within 1-4 months after surgical cyst removal. The detection of specific IgG and antigen in PEG precipitated immune complexes from false-negative/low responder Turkana hydatid sera, suggests that antibody 'mopping' by specific antigen may be occurring. After SDS-PAGE/immunoblotting analysis, antigen of mol. wt 67 000, present in hydatid cyst fluid and protoscoleces, was identified as putative circulating antigen in 3% PEG precipitates of sera from albendazole treated hydatid patients.

Lysosomal enzyme release from polymorphonuclear leukocytes induced by immune complexes of IgM and of IgG.

Lysosomal enzyme release by rabbit polymorphonuclear leukocytes induced by immune complexes of IgM or IgG antibodies and ovalbumin was studied by in vitro experiments. It was shown that IgM immune complexes in the form of precipitates were able to stimulate the release of the lysosomal enzymes beta-glucuronidase and alkaline and acid phosphatases, in contrast to heat-aggregated IgM, which had only a small effect. This stimulation was dependent on the presence of Ca2+ in the extracellular medium; Mg2+ showed a slight effect as a substitute for Ca2+. IgG precipitated immune complexes prepared from different regions of the precipitation curve were tested. It was shown that immune precipitates from the equivalence region were the most effective; those at antibody excess have a smaller but comparable capacity, whereas the precipitated immune complexes at antigen excess were the least effective. Soluble immune complexes of IgG with an excess of antigen concentration in the range of 2.5 to 5 times that of equivalence were also able to stimulate the enzyme release, but that capacity decreased rapidly with the increase in antigen concentration. The enzyme release induced by IgM immune complexes was not inhibited by competition with free immunoglobulin in the medium, either IgM or IgG in approximate physiologic concentrations; contrarily, with IgG immune complexes, free monomeric IgG (but not IgM) can completely block the process. The possible implications of these findings in the immune complex diseases are discussed.

Circulating immune complexes and antiglobulins (IgG and IgM) in asbestos-induced lung fibrosis

Thirty-nine asbestos workers were examined with respect to the presence of IgG and IgM antiglobulins and circulating immune complexes. The overall incidence of raised levels of IgM antiglobulins and immune complexes was 63 and 28%, respectively. In the group positive for immune complexes, IgM antiglobulins were found more frequently than in those asbestos workers lacking immune complexes. However, all cases with the highest levels of IgM antiglobulins had normal or only slightly elevated levels of immune complexes. IgG antiglobulin levels were not elevated in asbestos workers. Asbestos workers with IgG antinuclear antibodies had the highest incidence of elevated levels of immune complexes.

A simple method for determining polymeric IgA-containing immune complexes

A simplified assay to measure polymeric IgA-immune complexes in biological fluids is described. The assay is based upon the specific binding of a secretory component for polymeric IgA. In the first step, multimeric IgA (monomeric and polymeric) immune complexes are determined by the standard Raji cell assay. Secondly, labeled secretory component added to the assay is bound to polymeric IgA-immune complexes previously fixed to Raji cells, but not to monomeric IgA immune complexes. To avoid false positives due to possible complement-fixing IgM immune complexes, prior IgM immunoadsorption is performed. Using anti-IgM antiserum coupled to CNBr-activated Sepharose 4B this step is not time-consuming. Polymeric IgA has a low affinity constant and binds weakly to Raji cells, as Scatchard analysis of the data shows. Thus, polymeric IgA immune complexes do not bind to Raji cells directly through Fc receptors, but through complement breakdown products, as with IgG-immune complexes. Using this method, we have been successful in detecting specific polymeric-IgA immune complexes in patients with IgA nephropathy (Berger's disease) and alcoholic liver disease, as well as in normal subjects after meals of high protein content. This new, simple, rapid and reproducible assay might help to study the physiopathological role of polymeric IgA immune complexes in humans and animals.

Enhanced cAMP production by activated human Fc-IgG receptor positive T-cell subpopulations

Human peripheral T lymphocytes were separated into subpopulations on the basis of Fc-receptor expression or on the basis of their ability to rerosette with sheep red blood cells (SRBC) after incubation with theophylline. The baseline levels of cAMP in the Fc-receptor-positive and -negative subpopulations and in the theophylline-sensitive and -resistant subpopulations were equally low. However, within 5–30 min after stimulation with PGE 2 and theophylline, both the Fc-IgG receptor-positive T-cell subpopulation (T G) and the theophylline-sensitive T-cell subpopulation (T TS) showed greatly enhanced cAMP levels. Isoproterenol and theophylline also enhanced cAMP levels of the T G subpopulation more than in the T-non G subpopulation. In addition the T-non M subpopulation had higher stimulated cAMP levels than the T M subpopulation in the absence of Fc-IgG receptor interaction. This suggests that the Fc-IgG receptor-positive T cells are more responsive to stimulation of cAMP levels than the Fc-IgM receptor-positive subpopulation. However, since cAMP levels in T cells incubated with IgG-immune complexes were significantly higher than T cells incubated with IgM-immune complexes, the enhanced cAMP response of the T G subset can be attributed in part to a stimulating effect of Fc-IgG receptor interaction. Since the T G subpopulation and the T TS subpopulation have a greater capacity to produce cAMP, we hypothesize that cAMP may be involved in mediating the functionally distinctive properties of these human T-cell subpopulations.

Acute Non-A, Non-B Hepatitis With Serum Sickness-like Syndrome and Aplastic Anemia

We treated a patient in whom acute non-A, non-B hepatitis was complicated by a serum sickness-like syndrome (rash, arthralgias). Serum from this patient demonstrated a fall in C3, C4, and total hemolytic complement levels during the syndrome, in association with circulating IgM immune complexes. Fatal aplastic anemia developed later in the patient. This case illustrates that non-A, non-B hepatitis may be complicated by immune complex features that have previously been emphasized to occur with acute hepatitis B. Additional evidence supporting the occurrence of this clinical picture in non-B forms off viral hepatitis is presented.

Whipple's disease: A case with circulating immune complexes

A patient with Whipple's disease was studied for 56 wk from diagnosis, during which time he received continuous antibiotic therapy. Intramucosal bacillary bodies detected by electron microscopy disappeared within 12 wk and a threefold fall in anti-body titer to Hemophilus influenza type B bacillus occurred during this period. Circulating immune complexes of IgG class were consistently detected during the first 28 wk of treatment but not subsequently. IgM class immune complexes were detected at a time when mucosal recovery had occurred and when IgG complexes were no longer detectable. A further rise of IgM immune complexes could be induced by enteric challenge with bovine serum albumin in our patient but not in control subjects. The detection of serum immune complexes in Whipple's disease may reflect the entry of foreign antigen through intestinal mucosa. These observations also support the possibility of an underlying defect of antigen exclusion in this disorder, which persists despite apparent mucosal recovery.

Heterogeneity of human natural killer cell populations

Natural killing (NK) in human donors was determined by the ability of peripheral blood subpopulations to lyse the myeloid target, K562, in a 2 to 4 hr 51Cr release assay. The most active cell was a non-T cell which passed through nylon columns (representing 10 to 25% of column passed cells). A second column passed cell population, with characteristics of T lymphocytes (75 to 90% of column passed cells), was also capable of mediating natural killing. Non-T cells which were retained by the nylon columns (45 to 55% of adherent cells) lacked NK activity. However, nylon adherent T cells (45 to 55% of adherent cells) were consistently active in NK assays, illustrating an important subset of NK effector cell often overlooked. Both column passed and adherent T cells were further separated according to their ability to bind IgG or IgM immune complexes, showing that those mediating NK have receptors for IgG (Tγ+) but not for IgM (Tμ+).

Fc IgM receptors on human lymphoblastoid B cell lines

AbstractFive human lymphoblastoid cell lines have been investigated for their ability to secrete immunoglobulins (IgG, IgA, IgM) and for the presence of different cell surface markers, with special emphasis on the Fc IgM receptor, using a rosette technique with IgM‐coated bovine red blood cells (EA‐IgM).Four cell lines (Hu, 8432, SB, PA3) were characterized as having as cell origin due to the presence of surface immunoglobulins, complement receptors, mouse red blood cell rosette formation, low avidity Fc IgG receptors and absence of sheep red blood cell rosette formation. Two of these B cell lines (Hu and PA3) secreted IgM, two cell lines (8432 and SB) secreted IgG, while the human T cell line Molt 4 did not secrete Ig.All four B cell lines exhibited Fc IgM receptors (17–35%) while the T cell line Molt 4 had no detectable Fc IgM receptor. The receptor was specific for IgM. Neither aggregated IgG, soluble IgG immune complexes nor EDTA could abrogate the rosette formation, IgM immune complexes, pure human IgM, as well as normal human serum had an inhibitory effect on EA‐IgM rosette formation. The receptor was trypsin‐sensitive and required protein synthesis for expression.There was no correlation between the expression of Fc IgM receptors and secretion of any given Ig class, indicating that B cells may express Fc IgM receptors independently of their commitment to produce IgM or IgG.

Functional analysis of two human T-cell subpopulations: help and suppression of B-cell responses by T cells bearing receptors for IgM or IgG.

Subpopulations of thymus-derived T lymphocytes bearing receptors for either IgM or IgG molecules were isolated from human peripheral blood. Those with receptors for IgM (T.M) provided help in a cell dose-dependent fashion for the pokeweed mitogen-induced differentiation of B lymphocytes in vitro, whereas cells with receptors for IgG (T.G) did not. T.G cells, on the hand, efficiently suppressed the differentiation and proliferation of B cells in the pokeweed system in the presence of helper T.M cells. This suppressive activity of T.G cells required prior interaction of the T.G cells with immune complexes. The helper activity of T.M cells was relatively radioresistant while the suppressor activity of T.G cells was radiosensitive. The results indicate that helper and suppressor functions of human T lymphocytes in this model system are mediated by different subpopulations of T cells which can be distinguished by their ability to bind IgM or IgG immune complexes, respectively.