Detection and characterization of circulating immune complexes by ultracentrifugation. Technical aspects

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.

Immune complexes in serum of rats during infection with Plasmodium berghei

Large amounts of immune complexes were present in the serum of infected rats early in infection when parasitemias were low. As the infection progressed and parasitemia increased and then decreased, the amounts of immune complexes in the serum also fell. This result suggests that increased efficiency of complex clearance was an important factor in determining the levels of immune complexes in the serum. In high performance liquid chromatography (HPLC), the complexes in the serum migrated as a peak with material of 350 kDa and greater in mass. They sedimented in a sucrose gradient as a band with a sedimentation coefficient of 22 s, which was calculated to yield a mass of approximately 1100 kDa. Immunoelectrophoresis and radial immunodiffusion showed that IgG was the major immunoglobulin in the complexes. As the IgG content of the complexes increased, the levels of complexes in the serum generally decreased. HPLC analysis of precipitated complexes suggested that they contained loosely bound albumin. Serum proteins were affected by the infection. A depletion of free immunoglobulin was observed during the initial period of immune complex formation.

Immune complex assays: diagnostic and clinical application

The presence of circulating immune complexes have been described in many different human disease states but the significance of their presence has always been a subject for debate. Improvements in the methods of detecting immune complexes have demonstrated a wide degree of heterogeneity, which accounts for the difficulty in obtaining accurate and reproducible measurements, even in the same individual. Techniques for isolating individual complexes, characterizing their pathophysiological properties, and biochemically analyzing the nature of the complexed antigen are now being used to provide data that is helping to clarify the role of immune complexes in the pathogenesis of disease. In addition, such studies are also providing data which is proving that immune complexes have a potential role in immune regulation.

Primary lung cancer. A controlled study of preoperative and postoperative levels of circulating immune complexes

Three complement-dependent and one rheumatoid factor-dependent immune complex assays were used to analyze the sera taken before surgery from 70 unselected and previously untreated lung cancer patients, from 30 of them after surgery, and from 31 healthy controls. Plasma levels of complement split product C3d were also analyzed. The levels of circulating immune complexes (cIC) and C3d were essentially the same in samples taken from lung cancer patients before surgery and from healthy controls. By the four immune complex assays, increased levels were found in 0 to 10% of the preoperative lung cancer patients compared to 3% of the healthy controls (not significant). The postsurgical tumor, lymph node, metastasis (pTNM) stage of the lung cancer was not reflected in the levels of cIC or C3d. Paired comparisons of the cIC and C3d levels before and after surgery did not show significant differences. Thus, we found no evidence for the occurrence of cancer-related cIC in lung cancer patients.

A prospective study of circulating immune complexes in patients with breast cancer

Levels of circulating immune complex (cIC) and complement split product C3d were studied in 86 patients with breast cancer (BC), 22 patients with benign breast disease (BD), and 72 age- and sex-matched blood-bank donors (NC), using solid-phase Clq-protein A RIA, Clq-anti-IgG RIA, anti-C3d anti-IgG RIA, and polyclonal IgM-rheumatoid factor ELISA for clC detection. No significant differences in cIC and C3d levels were found between the groups. The incidence of raised cIC levels varied from 4.9 to 8.2% in the BC group and from 4.5 to 22.7% in the BD group in comparison with 2.9 to 3.0% in the NC group. Using the solid-phase polyclonal IgM-rheumatoid factor ELISA we found that the cIC levels of patients with stage-III cancer were significantly higher than those of patients with stage-I or stage-II cancer. However, the other tests showed no relationship to tumor burden. Likewise, an effect of mastectomy on the cIC levels was also only detectable by one of the assays, i.e., the post-mastectomy levels of cIC as measured by the solid-phase anti-C3d anti-IgG RIA were significantly lower than the pre-mastectomy levels. Serial analyses of cIC and C3d levels were performed pre-operatively, one month post-operatively and every 3 months during the first year after mastectomy in 46 of the patients. During a I-year observation period, 7 patients developed metastatic disease. The occurrence of metastatic disease was not, however, preceded by characteristic changes in serially determined cIC and C3d levels.

Isolation and characterization of circulating immune complexes from patients with pneumococcal pneumonia

Circulating immune complexes (CIC) were isolated from serum samples from patients with bacteremic and nonbacteremic pneumococcal pneumonia. Overall, 63% (26 of 41) of patients with pneumococcal pneumonia had elevated levels of immunoglobulin G (IgG)-containing CIC. IgM-containing CIC were identified in samples from only three patients. Serum samples from nonbacteremic patients contained significantly higher levels of IgG-containing CIC (96.6 +/- 111.7 micrograms/ml) than did samples from bacteremic patients (31.7 +/- 26.9 micrograms/ml) during week 1 in hospital (P less than 0.05). Immune complexes levels did not correlate with IgG concentrations in serum or anticapsular antibody levels. Immune complexes from nonbacteremic patients had sedimentation coefficients of greater than 19s by density gradient ultracentrifugation. In contrast, CIC from bacteremic patients had smaller coefficients, of between 9s and 14s. Pneumococcal capsular antigens were identified in concentrated dissociated CIC from both patient groups by counterimmunoelectrophoresis.

HBsAg: anti-HBs immune complexes. A method for separating the constituent components and assessment of the affinity of the antibody

A number of chemical disruption agents were assessed for their ability to dissociate HBsAg:anti-HBs immune complexes and to release both the antibody and antigen component in immunologically active forms. The most appropriate reagent was 0.1 M diethylamine which could elute up to 81% of anti-HBs antibody bound to solid-phase HBsAg and retained 93% of its antigen-combining activity. Complexes formed at various degrees of antigen excess and pre-exposed to 0.1 M diethylamine at room temperature for 18 h before ultracentrifugation on sucrose density gradients were effectively dissociated. The released antibody and antigen banded at their expected densities. However, the affinity of the isolated antibody for the detergent-solubilized polypeptide complex from purified HBsAg (gp30/p25) and cyclical peptides representing amino acids 124-137 and 139-147 of HBsAg were found to be considerably lower than that of the original pooled anti-HBs immunoglobulin used to form the immune complexes. These results suggest that the highest affinity antibody subpopulation may not be completely dissociated from the complex. Care should thus be exercised in the interpretation of the significance of the observed affinity of the antibody isolated by this and other similar dissociation procedures.

Preparative isolation of immune complexes from serum by sucrose gradient ultracentrifugation

Immune complexes were isolated by ultracentrifugation in sucrose gradients (20-65% (w/w]. the centrifugation procedure was demonstrated to be isopycnic. The banding density of the complexes was influenced by the chemical nature and molecular size of the antigen and by the antigen to antibody ratio. The method was applied for preparative isolation of immune complexes from patients with systemic lupus erythematosus, rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis, and uncomplicated psoriasis.

Suppression of mitogen-induced lymphocyte transformation by plasma from patients with hepatosplenic Schistosomiasis mansoni: role of immune complexes

Plasma from chronic or advanced hepatosplenic schistosomiasis (mansoni) patients (PCS) suppressed mitogen-induced responses of normal human peripheral blood mononuclear cells. 1 x 10(5) Ficoll-Hypaque isolated lymphocytes were cultured in 100 microliter RPMI 1640 media with 100 microliter plasma preparation and stimulated with phytohemagglutinin P (PHA), concanavalin A (Con A), pokeweed mitogen (PWM) and Staphylococcus aureus phage lysate (SPL). Compared to normal human plasma, dose-response experiments with 10-50% PCS uniformly inhibited the 72-h PHA, Con A and PWM responses with maximal suppression at 50% plasma concentration. At this concentration, the range of suppression was 42-60%. The inhibitory activity was unaffected by 56 degrees C, 30 min pretreatment of PCS. However, pre-culture of cells with PHA for 24 h prior to addition of 50% PCS abrogated the suppressor activity. Furthermore, 6-day cultures with PWM and SPL were not suppressed by 50% PCS. Plasma suppressor activity was nearly eliminated by pre-treatment of PCS with 4% (w/v) polyethylene glycol (PEG) in all cases. In the putative immune complexes in the PEG precipitates, Clq, C3, C4, IgG, IgM and IgA were identified in nearly all PCS samples. Schistosomal antigen was found in only two of 23 PCS samples tested and significant anti-schistosomal IgG antibodies were found in all PEG precipitates. The data suggest immune complexes (non-specific and specific) act to suppress 72-h mitogenic responses.

The specific detection of IgA in immune complexes

An assay to detect IgA in circulating immune complexes (IC) using low avidity goat IgM antibody against human polyclonal IgA is described. The binding of this antibody to IgA coupled to Sepharose 6B is inhibited by IgA-containing IC. The specificity and sensitivity of this anti-IgA inhibition assay (a-IgA-InhA), was evaluated with aggregated purified immunoglobulins, sera of patients with Henoch-Schönlein purpura and normal human sera. Aggregated immunoglobulins of the IgA class, but not monomeric IgA, were reactive. Sucrose density ultracentrifugation showed that large IgA constituents (greater than 19S) were found only in the sera of patients with Henoch-Schönlein purpura. Both these sera and normal human serum contained smaller IgA components (between 7S and 19S), probably small polymers of IgA, which were reactive in this assay and interfered with detection of IgA-containing IC. Redissolved precipitates obtained from normal serum with polyethylene glycol showed reduced reactivity in the test, whereas the inhibitory activity of IgA-containing IC in sera of patients with Henoch-Schönlein purpura was retained in the precipitates. Precipitation of sera with polyethylene glycol allowed detection of smaller quantities of IgA-containing IC in patients with Henoch-Schönlein purpura.

Circulating immune complexes in coccidioidomycosis. Detection and characterization

Estrogen-receptor-positive breast tumors are treated with anti-estrogen (AE) therapies but frequently develop resistance. Cancer stem cells (CSCs) with high aldehyde dehydrogenase activity (ALDH⁺ cells) are enriched following AE treatment. Here, we show that the interleukin-1β (IL-1β) signaling pathway is activated in ALDH⁺ cells, and data from single cells reveals that AE treatment selects for IL-1 receptor (IL1R1)-expressing ALDH⁺ cells. Importantly, CSC activity is reduced by an IL1R1 inhibitor in AE-resistant models. Moreover, IL1R1 expression is increased in the tumors of patients treated with AE therapy and predicts treatment failure. Single-cell gene expression analysis revealed that at least two subpopulations exist within the ALDH⁺ population, one proliferative and one quiescent. Following AE therapy the quiescent population is expanded, which suggests CSC dormancy as an adaptive strategy that facilitates treatment resistance. Targeting of ALDH⁺IL1R1⁺ cells merits testing as a strategy to combat AE resistance in patients with residual disease.

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Anti-estrogen-resistant ALDH⁺ cells have increased CSC activity in ER⁺ tumors

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The IL1R1-expressing ALDH⁺ CSC population expands after anti-estrogen treatment

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IL1R1 expression predicts anti-estrogen treatment failure

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Targeting of ALDH⁺IL1R1⁺ cells reverses anti-estrogen resistance

Circulating immune complexes in coccidioidomycosis. Detection and characterization

Sera of 22 patients with active and 13 with inactive coccidioidomycosis, as well as 15 healthy subjects who were skin-test positive to coccidioidin and 39 healthy subjects who were coccidioidin skin-test negative, were assayed for immune complexes. Circulating immune complexes were measured by the Clq-binding assay, the Clq-solid phase assay, the monoclonal rheumatoid factor inhibition assay, and the monoclonal rheumatoid factor solid phase assay. An increased concentration of circulating immune complexes was detected in 73% of those with active disease by at least one assay compared with 13% of the healthy controls. Significantly increased levels of immune complexes were detected in sera of patients with active coccidioidomycosis by the Clq-binding assay (P < 0.001), the Clq-solid phase assay (P < 0.001), the monoclonal rheumatoid factor inhibition assay (P < 0.005), and the monoclonal rheumatoid solid phase assay (P < 0.05) compared with the results obtained in the 54 healthy subjects. In contrast, those with inactive disease did not show significantly increased concentrations of circulating immune complexes. Sucrose density gradient ultracentrifugation of patients' sera established that the immune complexes were of intermediate size, sedimenting between the 6.6S and 19S markers. Immune complexes were shown to contain both coccidioidin antigen and anticoccidioidin antibody. In addition, a radioimmunoassay was developed to quantitate coccidioidin antigen-containing immune complexes. The latter assay proved highly sensitive in detecting immune complexes in patients with active coccidioidomycosis.

The isolation of immune complexes containing IgM rheumatoid factor and recovery of IgG rheumatoid factor from the complexes

IgG with rheumatoid factor activity has been recovered from immune complexes containing IgM rheumatoid factor. This was done by passing serum from patients with rheumatoid arthritis through an immunoadsorbent column of the F(ab')2 fragment of rabbit anti-human mu chain. The recovered IgM was analysed by radioimmunoassays for IgM and IgG rheumatoid factors before and after sucrose density gradient centrifugation at neutral and acid pH. It is considered that the method may be generally applicable for the isolation of immune complexes containing IgM antibodies.