Antibodies against C1q in patients with systemic lupus erythematosus

The first component of the classical pathway of complement (C1q) is considered to be involved in the pathogenesis of systemic lupus erythematosus (SLE). This view is based on the observation that a substantial number of patients with SLE develop hypocomplementemia with depletion of the classical pathway components, and C1q has been shown to play an important role in the clearance of immune complexes and apoptotic bodies. In addition, homozygous C1q deficiency is the strongest disease susceptibility gene for the development of SLE that has been characterised in humans. However, most SLE patients have no primary complement deficiency. Hypocomplementemia in SLE patients is a secondary event and often associated with antibodies against C1q (anti-C1q). Although anti-C1q have been found in a number of distinct autoimmune disorders, they are best described in patients with SLE where they strongly correlate with renal flares. Current data suggest that the occurrence of anti-C1q in SLE patients is necessary but not sufficient for the development of proliferative lupus nephritis, suggesting an interference with the normal function of the complement system.     

C1q solid-phase radioimmunoassay: binding properties of solid-phase C1q and evidence that C1q-binding IgG complexes in systemic lupus erythematosus are not bound to endogenous C1q

The binding properties of C1q solid-phase radioimmunoassay (C1q SPRIA) were examined, using heat-aggregated IgG (HAG) as the model of immune complexes (IC). The free, liquid-phase C1q, which was added to the C1q-coated tubes prior to the addition of HAG, had little inhibitory effect on binding of HAG to the solid-phase C1q, suggesting that the solid-phase C1q has a higher affinity for HAG than the liquid-phase C1q. On the other hand, more than 60% inhibition was seen when HAG was preincubated with the liquid-phase C1q. These binding properties of HAG to the solid-phase C1q in the presence of the liquid-phase C1q were not essentially altered by the heat inactivation or the addition of EDTA, suggesting that these pretreatments are not essential in C1q SPRIA. Next, in similar kinds of experiments, the binding properties of C1q-binding IgG complexes in SLE sera were investigated. In contrast to HAG, the binding capacity of IgG complexes in SLE sera to the solid-phase C1q was not inhibited by the preincubation with excess liquid-phase C1q. These findings suggest that C1q-binding IgG complexes in SLE sera detected by C1q SPRIA may not be bound to endogenous C1q in the circulation.     

Detection of autoantibodies against the globular domain of human C1q in the sera of systemic lupus erythematosus patients

The anti-C1q antibodies present in systemic lupus erythematosus (SLE) patients' sera are associated with renal involvement and the titer of these autoantibodies correlates with the clinical activity of the disease. It has previously been shown that anti-C1q antibodies bind neo-epitopes within the collagen region of human C1q. Evidence that these polyclonal autoantibodies recognize epitopes within the globular domain (gC1q) of the molecule has not been documented. In this study, we screened, using ELISA, a number of sera from SLE patients for the presence of anti-gC1q autoantibodies using recombinant globular head regions of individual A (ghA), B (ghB) and C (ghC) chains of human C1q. The recombinant proteins were used as test antigens to determine the levels of autoantibodies directed against ghA, ghB and ghC. SLE sera, containing high levels of anti-C1q antibodies, showed differentially increased binding towards ghA and ghB, which suggested that the gC1q domain can also be target of anti-C1q antibodies generated in SLE patients. Such antibodies can have severe pathophysiological consequences since these are likely to further impair the ability of C1q to clear immune complexes.     

Anti-thyroid peroxidase antibody activity in sera of patients with systemic lupus erythematosus.

Although patients with SLE have autoantibodies to thyroid peroxidase (TPO), IgG from sera of SLE patients does not inhibit TPO activities, in contrast with IgG from sera of patients with thyroid disorders. This finding suggests that the specificities of anti-TPO autoantibodies in SLE are different from those in cases of thyroid disorders. These autoantibodies to TPO should be considered when searching for associations between SLE and autoimmune thyroid disorders.     

Fibronectin binds to C1q: possible mechanisms for their co-precipitation in cryoglobulins from patients with systemic lupus erythematosus

Fibronectin and C1q frequently co-precipitated in cryoglobulins from patients with SLE. As a portion of the C1q molecule is similar to collagen to which fibronectin has a high affinity, we studied whether fibronectin specifically bound to C1q. Fibronectin was found to bind to both native and heat-inactivated C1q. The binding was enhanced by Ca++ and low ionic strength. We have also demonstrated that fibronectin is capable of binding to C1q fixed to immune complexes. The interaction between fibronectin and C1q may play a role in cryoglobulin formation and in clearance of immune complexes by reticuloendothelial system.     

An inhibitory factor against monocyte spreading in the sera of patients with systemic lupus erythematosus

The effect of the sera of patients with systemic lupus erythematosus (SLE) on monocyte function was studied using cell spreading as an indicator. Monocyte spreading induced by exogenous stimuli was shown to be inhibited by SLE sera. Gel filtration of SLE sera on Sephadex G-200 revealed that the factor responsible for this inhibition had a molecular weight of about 50,000. Pretreatment of monocytes with the inhibitory factor led to suppression of cell spreading induced by subsequent stimulation, but this hyporeactivity was reversible. Spreading of monocytes was rapidly aborted by the addition of this inhibitory factor. Thus, the inhibitory factor appeared to affect monocyte itself, but its effect seemed to be transient.     

血清抗C1q抗体在系统性红斑狼疮疾病活动性判断及狼疮肾炎诊断中的价值

目的探讨抗C1q抗体(C1qAb)在系统性红斑狼疮(SLE)活动性及狼疮肾炎(LN)诊断和疾病活动性判断中的价值。方法采用酶联免疫吸附法检测SLE患者(n=89)、疾病对照组(n=56)和正常对照组(n=42)血清中的抗C1q抗体阳性率,并与SLE患者临床实验室指标﹑活动性评分进行分析。结果 C1qAb的阳性率在SLE患者中显著高于疾病对照组和正常对照组患者(P<0.05);C1qAb阳性的SLE患者肾损发生率、活动性狼疮发生率及抗dsDNA抗体的阳性率均高于C1qAb阴性患者(P<0.05);C1qAb与SLEDAI活动性评分、抗核小体抗体(anti-nucleosome antibody,AnuA)及抗dsDNA抗体呈正相关(P<0.05)。结论抗C1q抗体对SLE的诊断和疾病活动性判断有重要价值;抗C1q抗体参与了SLE肾脏损害的发病机制。     

抗 C1q 抗体及补体 C3、C4 在神经精神性狼疮诊断中的应用价值

目的:探讨抗C1q 抗体及补体C3、C4 在神经精神性狼疮诊断中的应用价值。方法:对22 例狼疮脑病及66例SLE 患者进行横断面研究。抗C1q 抗体采用ELISA 方法,C3 及C4 采用免疫比浊法检测。分析补体与狼疮脑病的临床表现相关性,采用Logistic 回归分析狼疮脑病的危险因素。结果:NPSLE 患者抗C1q 抗体水平明显高于非NPSLE 患者,补体C4明显低于非NPSLE 患者,采用ROC 曲线分析抗C1q 抗体诊断NPSLE 敏感性及特异性分别为63.6%、66.7%。单因素分析后发现抗C1q 抗体、抗核糖体P 蛋白抗体、抗核小体抗体与神经精神性狼疮相关,但多因素Logistic 回归分析并未发现其与狼疮脑病发生有关。补体C4 降低与SLE 患者脑血管意外发生有关。结论:抗C1q 抗体在狼疮脑病诊断中具有一定的诊断价值,且补体C4 可能参与狼疮脑病脑血管意外的发生。     

A solid phase radioimmunoassay for detection of serum autoantibodies in systemic lupus erythematosus.

Solid phase radioimmunoassay (RIA) methods for measuring autoantibodies in systemic lupus erythematosus (SLE) patients' serum were developed to improve the sensitivity and quantitative precision of these determinations. Two mechanical systems were studied: (1) acetone fixed cell monolayers in glass tubes and (2) antigen coated plastic beads. Both systems were sensitive and reproducible, giving serum dilution end-points between two and four orders of magnitude (100-10,000 times) greater than those obtained by fluorescence microscopy. The most sensitive, versatile system involves the coating of plastic beads with nuclear antigen(s), incubation overnight with sera and labelling with 125I conjugated antihuman globulin. Linear binding of this radioactive tag is obtained over a wide range of SLE serum dilutions and the slopes of the serum dilution titration curves are almost identical for all SLE patients' sera we have tested. Therefore, a standard titration curve can be constructed from the results with a positive serum, and end-point dilutions of unknown sera estimated from results obtained with a single serum dilution. Alternatively, binding ratios of unknown sera can be usefully compared at fixed dilutions with standard positive and negative sera. For example, high binding ratios (greater than 3.0) were obtained with 19/20 SLE sera and 0/20 control sera. Antigens used in these systems include crude, whole-cell lysates and lysates from purified nuclei. These RIA methods appear to provide certain advantages over existing autoantibody assay methods because they are relatively simple, sensitive, reproducible and potentially capable of measuring a variety of autoantibody specificities.     

Microhemagglutination test for the detection of nucleoprotein antibody in systemic lupus erythematosus.

A simple and practical microhemagglutination test that detects two antibodies, one showing reactivity to the DNA moiety of soluble nucleoprotein (sNP) and the other to the DNA-histone complex of sNP, is described. The method incorporates human erythrocytes formalinized at 30 C., tanned, and coated with sNP at 37 C. Antibody specificity was determined by inhibition experiments performed on sera with added DNA or sNP antigen. With the indirect LE cell technic, evidence that the anti-sNP antibody detected in this work is related to the serum LE factor commonly associated with the LE cell phenomenon was obtained. The hemagglutination test is helpful in establishing the specific diagnosis of systemic lupus erythematosus (SLE) and may be used to follow the course of the disease and response to therapy in SLE patients, as this is a semiquantitative technic and rise or fall in titer or antibody can be determined.     

Anti-heparan sulphate reactivity in sera from patients with systemic lupus erythematosus with renal or non-renal manifestations.

Previously, we have shown that anti-DNA can bind to heparan sulphate (HS), a constituent of the glomerular basement membrane (GBM). We hypothesized that binding of anti-DNA to HS in the GBM plays a role in the onset of systemic lupus erythematosus (SLE) nephritis. To test this hypothesis we measured the anti-HS reactivity in cross-sectional and longitudinal studies of SLE patients with or without nephritis. In the transverse serum study single serum samples from 26 SLE patients were studied. We found no correlation between anti-HS reactivity and previously development of nephritis (anti-HS positive: seven out of 16 with history of nephritis, two out of 10 without nephritis). However, six of the seven anti-HS positive sera in the nephritis group were obtained within 1 month of the onset of nephritis, suggesting a temporal relationship between anti-HS reactivity and onset of nephritis. In the longitudinal serum study between six and 16 serum samples were studied from each of 10 SLE-patients. In five out of five episodes of nephritis we found anti-HS reactivity before the onset or exacerbation of the nephritis. In four non-renal manifestations anti-HS reactivity was found in only one episode; in none of the three patients who remained clinically stable did serum samples show anti-HS reactivity. Anti-HS reactivity was only found in sera positive for anti-DNA by Farr assay but the anti-HS titre was not a mere reflection of the reactivity measured in the Farr assay. This indicates that only a subpopulation of anti-DNA can bind to HS. We found a high correlation (r = 0.99) between anti-HS reactivities in plasma and serum and we conclude that anti-HS reactivity in serum samples from SLE patients is not due to in vitro complex formation during clotting. Although further prospective analysis is necessary, our data suggest that measurement of anti-HS reactivity in SLE patients might identify patients at risk for the development of nephritis.     

Complete functional C1q deficiency associated with systemic lupus erythematosus (SLE).

A complete functional deficiency of C1q is described in a patient suffering from SLE. From reduced plasma C1 activity of the parents a hereditary trait was assumed. The defective C1q molecule was haemolytically inactive, did not bind to immune complexes, and was not recognized by the monocyte C1q receptor. C1 activity in the patient's serum could be restored by the addition of purified C1q. Analysis by gel-filtration and ultracentrifugation experiments revealed an immunoreactive molecule of about 150 kD mol. wt, corresponding to one structural subunit of the C1q macromolecule, containing two A chain-B chain dimers and a C-C chain dimer. Applying Southern blot analysis with cDNA clones encoding for the three individual chains of the C1q molecule, no restriction fragment length polymorphism was detected, ruling out possible major alterations of the genetic information.     

Specific detection of circulating DNA:anti-DNA immune complexes in human systemic lupus erythematosus sera using murine monoclonal anti-DNA antibody.

The presence of DNA-anti-DNA immune complexes in sera from patients with systemic lupus erythematosus (SLE) was investigated by a new solid phase radioimmunoassay (RIA). This assay used murine monoclonal anti-double stranded DNA (dsDNA) antibody to recognize DNA present in the complexes and 125I-rabbit anti-human gamma globulin as a tracer. DNA-anti-DNA immune complexes were found in certain SLE sera but not in sera from patients with other immune complex diseases and from healthy blood donors. The presence of circulating DNA-anti-DNA complexes was associated with low C4 levels. It was not related to the presence of immune complexes detected by the polyethylene glycol assay suggesting either that the assay did not detect all DNA-anti-DNA complexes or that other antigen-antibody systems constitute the major immune complex components in SLE sera. The clinical significance of circulating DNA-anti-DNA complexes in SLE sera as well as the potential use of this solid phase RIA using various monoclonal antibodies to detect specific antigen-antibody systems is discussed.     

Anti-mannose binding lectin antibodies in sera of Japanese patients with systemic lupus erythematosus

Mannose-binding lectin (MBL) is a key element in innate immunity with functions and structure similar to that of complement C1q. It has been reported that MBL deficiency is associated with occurrence of systemic lupus erythematosus (SLE). We hypothesized that anti-MBL antibodies, if present, would affect the occurrence or disease course of SLE, by reduction of serum MBL levels, interference of MBL functions, or binding to MBL deposited on various tissues. To address this hypothesis, we measured the concentration of anti-MBL antibodies in sera of 111 Japanese SLE patients and 113 healthy volunteers by enzyme immunoassay. The titres of anti-MBL antibodies in SLE patients were significantly higher than those in healthy controls. When the mean + 2 standard deviations of controls was set as the cut off point, individuals with titres of anti-MBL antibodies above this level were significantly more frequent in SLE patients (9 patients) than in controls (2 persons). One SLE patient had an extremely high titre of this antibody. No associations of titres of anti-MBL antibodies and (i) genotypes of MBL gene, (ii) concentrations of serum MBL, or (iii) disease characteristics of SLE, were apparent. Thus, we have confirmed that anti-MBL antibodies are indeed present in sera of some patients with SLE, but the significance of these autoantibodies in the pathogenesis of SLE remains unclear.