Immune complexes in man: detection and clinical significance

Indoor-related microbe damage induces complement system activation in building users

In this comparative study, serum complement system antimicrobial activity was measured from 159 serum samples, taken from individuals from microbe-damaged (70 samples) and from reference buildings (89 samples). Antimicrobial activity was assessed using a probe-based bacterial Escherichia coli-lux bioluminescence system and comparison was made at a group level between the experimental and reference group. The complement activity was higher in users of microbe-damaged buildings compared with the reference group and the significant (P < 0.001) increase in activity was found in the classical reaction pathway. This study strengthens our notion that exposure to indoor-related microbe damage increases the risk for systemic subclinical inflammation and creates a health risk for building users.

Immune Complexes and Complement in Serum and Synovial Fluid of Rheumatoid Arthritis Patients

Rheumatoid arthritis (RA) is predominantly an intraarticular inflammatory and autoimmune disease that involves different autoantibodies and effector mechanisms. The aim of the study was to determine the utility of Circulating Immune Complexes (CIC) and complement components (C3c, C4) as possible markers for the disease activity in laboratory diagnostics. In a cross-section study 59 patients, according to the clinical criteria, were categorized into two groups: group with moderate (MA, n=24), and group with severe activity (SA, n=35) of RA. The concentration of CIC, C3c and C4 in sera (S) and synovial fluids (SF) was examined by an immunonephelometric method in both groups and compared with values in the control group (n=15) of patients with lesions of the menisci. Obtained results showed that there was no statistical significance in the values of C3c and C4, in both biological fluids, among all tested groups. Significant differences were found in the levels of CIC in both fluids, while testing the parameters (× ± SD, IU/mL) in the sera of groups with SA and MA of RA: 7.43 ± 13.40; 3.01 ± 2.92 (p<0.05) and SF: 13.47 ± 21.1, 5.33 ± 7.53 (p<0.001), respectively. These differences were higher between the group with SA and CG. Results for the concentrations of CIC were significantly higher in SF compared to sera: in the RA group with SA by 77% and group with MA by about 82%. These data could provide a confirmation of the hypothesis about local, intraarticular autoantibodies and subsequent CIC production. It can be concluded that the examination of CIC concentration in serum, and where it is possible in SF, is a useful marker of disease activity in RA patients, in contrast to the tested components of the complement. This statement does not exclude their consumption within immune effector mechanisms, but elicits the possibility that lower molecular fragments (C3d, C4d), as well as the novel activation products, could be better disease activity markers in RA patients.

Sensitivity and specificity of isolated antigen fromPlasmodium falciparum culture supernatant

Immunological sensitivity and specificity properties of isolated Plasmodium falciparum (GPL) antigen from culture supernatant have been measured and compared with malarial antigens and non malarial filtered paper blood sera for potency and efficacy. Latex bead coded GPL, Pf and RESA antigens immunoreaction properties of human filter paper blood samples (FPB) were studied by laser light scattering immunoassay (LIA) and Enzyme linked immunoabsorbent assay (ELISA) techniques. Results of GP. antigen sensitivity study by LIA method showed a very high malaria antibody binding response (MABR) i.e. 6% compared with 78% with RESA and 88% Pf antigens. Malaria detection by ELISA method also found similar results. Specificity study of GPL antigen for different non malarial filter paper blood sera (NMFS) showed no immunoreaction however Pf and RESA antigen showed few positive immunological responses. These results suggest that sensitivity and specificity properties of isolated GPL antigen is better than other antigens.

A quantitative approach to the determination of antigen in immune complexes

Immune complexes are present in the circulation of healthy individuals and the formation of such complexes is part of a normal immune process. During some pathological conditions, significant amounts of immune complexes are formed and deposited in the kidney and other tissues, causing severe injury. Since the levels of immune complexes can provide valuable prognostic information, dozens of methods have been developed to detect and quantify these complexes. However, many of these methods are non-specific, not quantitative, and give false-positive results. Methods based on detecting the antigen portion of immune complexes can yield more precise information about circulating immune complexes. We have used a quantitative dot-blot assay, which permits detection of antigen even if buried, to determine the levels of antigen in circulating immune complexes. In healthy donors, significant amounts of immune complexes containing DNA and beta(2)-glycoprotein I were detected (natural immune complexes). Natural immune complexes with Lewis X antigen were also observed in the circulation of healthy persons. In experimentally induced murine systemic lupus erythematosus (SLE) and SLE patients, there was a correlation between the clinical manifestations and the levels of DNA in the circulating immune complexes. At severe SLE flares, the level of DNA in circulating immune complexes decreased, probably due to tissue deposition of immune complexes. The low levels of DNA in immune complexes circulating in SLE patients correlated with low serum concentrations of the complement component C1q. No direct correlation was found between the levels of circulating anti-dsDNA antibodies and DNA in immune complexes. Thus, quantitation of antigen levels in circulating immune complexes can be used to determine the prognosis of autoimmune diseases.

Difference and ratio plots: simple tools for improved presentation and interpretation of scientific data. Unexpected possibilities for the use of the conglutinin binding assay in inflammatory rheumatic diseases

11111onglutinin-binding assay (KgBa) has gained widespread use for the detection of circulating immune complexes. A recent paper questioned the interpretation of the results obtained by this method and the validity of the assay (Holmskov et al. (1992) J. Immunol. Methods 148, 225). We now present hitherto unnoted differences between controls and patients with either rheumatoid arthritis or systemic lupus erythematosus. For this we use simple, but unconventional, graphic representations of the data, based on difference plots and ratio plots. Differences between patients with Burkitt's lymphoma and systemic lupus erythematosus from another previously published study (Macanovic, M. and Lachmann, P.J. (1979) Clin. Exp. Immunol. 38, 274) are also represented using ratio plots. Our observations indicate that analysis by regression analysis may often be misleading.

Bovine conglutinin (BC) mRNA expressed in liver: cloning and characterization of the BC cDNA reveals strong homology to surfactant protein-D

Bovine conglutinin (BC) is a C-type lectin isolated from bovine serum that appears to play a role in first-line host defense. The BC cDNA was cloned from a bovine liver library and the nucleotide (nt) sequence of 1519 bp was determined. The longest open reading frame encoded a 20-amino-acid (aa) signal sequence and a mature protein of 351 aa. Analysis of the nt and deduced aa sequences revealed 87 and 78% identity, respectively, with the sequences of another vertebrate lectin: bovine surfactant protein-D (SP-D). Of interest, the expression of the BC mRNA, as determined by RNase protection assay, is restricted to liver, unlike bovine SP-D, a lung-surfactant protein.

Somatic cell mapping of conglutinin (CGN1) to cattle syntenic group U29 and fluorescence in situ localization to Chromosome 28

A 260-bp genomic PstI fragment, which encodes a portion of the carbohydrate recognition domain, was used along with hybrid somatic cells to map the conglutinin gene (CGN1) to domestic cow (Bos taurus) syntenic group U29. In turn, a cosmid containing the entire bovine CGN1 was used with fluorescence in situ hybridization to sublocalize this gene to cattle Chromosome (Chr) (BTA) 28 band 18. Since BTA 28 and several of the other small acrocentric autosomes of cattle are difficult to discriminate, we have also chromosomally sublocalized CGN1 to the p arm of the lone biarmed autosome of the gaur (Bos gaurus). The use of the gaur 2/28 Robertsonian as a marker chromosome and our assignment of CGN1 to BTA 28 should help resolve some of the nomenclatural questions involving this cattle chromosome.

Calcium-dependent and calcium-independent signals in the conglutinin-binding assay (KgBa) for immune complexes. Influence of anti-collagen-antibodies

A solid phase ELISA conglutinin-binding assay (KgBa) was evaluated for the detection of circulating immune complexes. ELISA wells were coated with purified bovine conglutinin and incubated with test sera. Bound IgG was detected with enzyme labelled anti-immunoglobulin. Heat aggregated IgG which had been "solubilized" (i.e., complement treated by incubation with serum) was employed as a reference. The binding of the complement-reacted IgG to solid phase conglutinin was found to be calcium-dependent and inhibitable with N-acetyl-D-glucosamine (GlcNAc). Prolonged incubation (4 days) of aggregated IgG with serum at 37 degrees C abolished the binding to conglutinin, a finding consistent with the complete degradation of deposited C3b to C3c and C3d. The solubilized IgG that bound to solid phase conglutinin was found by gel chromatography to be of high molecular weight (greater than 600 kDa). Binding of IgG to solid phase bovine conglutinin was also observed to a variable degree in normal and pathological sera. However, in this situation the IgG binding was largely calcium-independent, was not inhibited by GlcNAc and did not decrease after prolonged incubation of the serum at 37 degrees C. The reactive IgG eluted on gel chromatography at the position of monomeric IgG suggesting binding via the antigen binding sites. Binding of this IgG was inhibited by both collagen type II and purified conglutinin. These observations suggest that the assay detects cross-reacting autoantibodies against collagen epitopes, or, alternatively, antibodies against the dietary antigen, bovine conglutinin.

Circulating immune complexes in leukaemias and lymphomas

Circulating immune complexes (ClC) were estimated in 78 patients of leukaemias and lymphomas by Clq deviation ELISA and PEG assay. In all leukaemias a significant elevation in ClC was seen at the time of first presentation. While in ALL a decrease occurred on therapy as partial or complete remission was achieved, no such fall was seen in AML or CML-BC when treated. ClC levels were much higher in non-Hodgkins lymphoma than in Hodgkins disease and showed a direct correlation with B symptoms and activity of the disease. The ClC levels were highest in null-ALL followed by those in common ALL and T-ALL. The mean duration of remission in patients of ALL without elevation in ClC was much longer than in those with ClC.

Immunoglobulin isotype composition of circulating and intra-articular immune complexes in patients with inflammatory joint disease

The immunoglobulin (Ig) heavy chain isotype composition of intra-articular and circulating immune complexes (ICs) were determined by a Raji cell flow cytometric assay in paired serum and synovial fluid samples from 15 patients with rheumatoid arthritis (RA) and 15 patients with other articular diseases (osteoarthritis, ankylosing spondylitis, gout, psoriatic arthritis, Reiter's disease). ICs were most prevalent in synovial fluid samples of patients with RA but were infrequently detected in serum and synovial fluid samples from the non-RA patients. ICs in patients with RA were heterogeneous both in the prevalence of Ig subclasses identified and in the distribution of the respective Ig isotypes within the complexes. Furthermore, differences were observed in the Ig isotype composition of ICs in paired serum and synovial fluid samples indicating that circulating ICs may not always arise simply by spill-over from articular sites. The possible mechanisms for IC formation in RA are discussed with reference to four patients who displayed features of extra-articular disease.

Characterisation of the size and composition of circulating immune complexes in patients with rheumatoid arthritis

The size and composition of circulating immune complexes in the sera of patients with rheumatoid arthritis (RA) were studied in relation to different manifestations of the disease. Circulating immune complexes from the sera of 94 patients (50 with extra-articular disease) and 10 matched controls were fractionated by sucrose density gradient ultracentrifugation. The composition, immunoglobulin and rheumatoid factor (RF) concentrations within each of the fractions were determined by a sensitive enzyme linked immunosorbent assay (ELISA). Intermediate size (14S-21S) IgG complexes containing RF activity and 22S IgG-IgM RF complexes were found in the sera of 40 patients with RA, while intermediate size complexes of self associated IgG RF and larger size complexes (greater than 22S) of IgG RF and IgM RF were associated with extra-articular features of RA (50% of extra-articular disease). Complexes containing IgA were found in the sera of many patients with RA, and dimeric IgA RF mainly in patients with extra-articular disease. These results support the view that whereas small size circulating immune complexes are of no primary pathogenic importance in synovitis, large size (greater than 22S) circulating immune complexes may play a role in extra-articular disease in RA. Current understanding of the formation of large complexes provides a biological explanation for their occurrence and effects.

Levels of soluble CD8 antigen and circulating immune complexes in intravenous drug abusers: relationships to HIV antibody serology

A total of 36 intravenous drug abusers (IVDA) were studied for circulating immune complexes (CIC) and serum soluble CD8 antigen (sCD8). None had symptoms or signs of AIDS-related complex or AIDS. sCD8 levels were significantly higher in 18 patients who had HIV antibody (Ab) compared with 18 patients who were HIV Ab negative (1640 +/- 578 virus 804 +/- 264 U/ml, p less than 0.0001). In HIV Ab+ patients but not in HIV Ab- patients, sCD8 levels significantly correlated with percentages and absolute numbers of activated CD3+DR+ peripheral blood mononuclear cells (p = 0.0024 and 0.0183, respectively). Also in HIV Ab+ patients, CIC levels were significantly greater for both anti-C3 binding (13.1 +/- 11.1 versus 2.9 +/- 3.4 micrograms/ml, p = 0.002) and C1q binding (23.5 +/- 20.2 versus 6.3 +/- 4.3 micrograms/ml, p = 0.001) CIC. Serum C4 concentrations were lower in the HIV Ab+ patient group (33.9 +/- 10.1 versus 41.6 +/- 12.4 mg/dL, p = 0.043). In the seropositive group, IgG levels were higher (2206 +/- 859 versus 1615 +/- 645 mg/dl) and total CD4 cell counts were lower (757 +/- 344 versus 1172 +/- 402 cells per mm3), but at a less significant level (p = 0.024 and 0.005, respectively), than that seen for sCD8 and C1q CIC differences. These results suggest that elevations of both the lymphocyte activation marker sCD8 and antigen nonspecific CIC characterize earlier stages of HIV infection in IVDA.

Enzyme immunoassay detection of circulating immune complexes by monoclonal antibodies to C3 neoepitopes with special reference to IgG concentration and to interfering anti-immunoglobulin antibodies

A sensitive solid-phase anti-C3 enzyme immunoassay for detection of circulating immune complexes (CIC) is described. A mixture of the monoclonal antibodies (MoAbs) bH6 and Clone 9 specific for neoepitopes on C3 activation products was used as capture reagent. MoAb bH6 recognized C3b, iC3b and C3c, and Clone 9 recognized iC3b and C3dg. Detection antibody was a polyclonal peroxidase-conjugated rabbit anti-human Ig antiserum. A quantitative assay was constructed using serum incubated with heat aggregated IgG (HAG) as standard. The lower detection limit was 5 micrograms/ml of HAG. Interassay and intra-assay coefficient of variation was 15% and 5%, respectively. Anti-animal immunoglobulin antibodies were detected both in normal and pathological sera. This activity was efficiently absorbed by nonimmune immunoglobulins added to the samples. The present assay was compared with a polyethylene glycol precipitation assay for CIC determination. The latter assay was strongly influenced by the IgG concentration (rs = 0.78; P = 0.006), whereas no such correlation was seen for the anti-C3 immune complex assay (rs = -0.30; P = 0.20).

Circulating immune complexes after splenectomy

Circulating immune complexes were evaluated in 25 patients (age range 10 to 46 years) who had undergone splenectomy for non-malignant conditions by studying a polyethylene glycol insoluble serum fraction. Although the extent of binding to Clq was within normal limits, these patients had increased concentrations of factor B in the immune complex serum fraction. These findings indicate that an unusual type of circulating immune complex may be detected after splenectomy, suggesting a possible role for the spleen in the removal of circulating immune complexes.

Yersinia specific immune complexes in the synovial fluid of patients with yersinia triggered reactive arthritis

Yersinia specific immune complexes were demonstrated in the synovial fluid of three patients out of 12 with yersinia triggered reactive arthritis. They were not detectable in the synovial fluid of any of the 16 control patients, including nine with reactive arthritis triggered by factors other than yersiniae. Platelet reactive IgG was detectable in the synovial fluid of eight out of the 12 patients with yersinia triggered reactive arthritis and in three of the 16 control patients, all three having rheumatoid arthritis. An enzyme linked immunosorbent assay and a platelet 125I labelled staphylococcal protein A test were used to measure yersinia specific immune complexes and platelet reactive IgG respectively. The results obtained show for the first time the occurrence of bacterial antigens, derived from the causative strain, in the synovial fluid in yersinia triggered reactive arthritis.

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.