Anti-C1q autoantibodies amplify pathogenic complement activation in systemic lupus erythematosus

Patients with systemic lupus erythematosus (SLE) often develop glomerulonephritis (i.e., inflammation in the glomeruli of the kidney), commonly referred to as lupus nephritis. Patients with lupus nephritis typically have autoantibodies to the complement classical pathway protein C1q. Whether these anti-C1q antibodies play any role in the development of lupus nephritis has been unclear. In this issue of the JCI, a new study demonstrates that anti-C1q antibodies can amplify glomerular injury but only when they are bound within the glomerulus to C1q that has been already brought to that site by other types of glomerular-reactive autoantibodies. These studies are the first, to our knowledge, to provide a causal link between anti-C1q antibodies and target organ damage in SLE.

Anti-C1q autoantibodies deposit in glomeruli but are only pathogenic in combination with glomerular C1q-containing immune complexes

Anti-C1q autoantibodies are present in sera of patients with several autoimmune diseases, including systemic lupus erythematosus (SLE). Strikingly, in SLE the presence of anti-C1q is associated with the occurrence of nephritis. We have generated mouse anti-mouse C1q mAb's and used murine models to investigate whether anti-C1q autoantibodies actually contribute to renal pathology in glomerular immune complex disease. Administration of anti-C1q mAb JL-1, which recognizes the collagen-like region of C1q, resulted in glomerular deposition of C1q and anti-C1q autoantibodies and mild granulocyte influx, but no overt renal damage. However, combination of JL-1 with a subnephritogenic dose of C1q-fixing anti-glomerular basement membrane (anti-GBM) antibodies enhanced renal damage characterized by persistently increased levels of infiltrating granulocytes, major histological changes, and increased albuminuria. This was not observed when a non-C1q-fixing anti-GBM preparation was used. Experiments with different knockout mice showed that renal damage was dependent not only on glomerular C1q and complement activation but also on Fcgamma receptors. In conclusion, anti-C1q autoantibodies deposit in glomeruli together with C1q but induce overt renal disease only in the context of glomerular immune complex disease. This provides an explanation why anti-C1q antibodies are especially pathogenic in patients with SLE.

A role for mannose-binding lectin dysfunction in generation of autoantibodies in systemic lupus erythematosus

OBJECTIVE

To investigate the possible association of the mannose binding lectin (MBL) pathway of complement activation with different disease parameters and disease activity in patients with systemic lupus erythematosus (SLE).

METHODS

MBL genotype, MBL serum concentration, MBL complex activity and MBL pathway activity were assessed in 53 patients. The activity of the MBL-MASP complex was assessed on the basis of its ability to activate exogenous C4. For MBL pathway activity the formation of the terminal complex of complement activation (C5b-9) was measured. Results were analysed in relation to clinical variables and autoantibody profiles in these patients.

RESULTS

MBL complex activity and MBL pathway activity were both reduced in patients carrying MBL variant alleles. Anticardiolipin and anti-C1q autoantibodies were observed significantly more frequently in patients with MBL variant alleles. Furthermore, the presence of these autoantibodies was associated with a decreased MBL concentration and function. In contrast, anti-MBL autoantibodies were not found in patients with MBL variant alleles, possibly related to impaired binding of variant MBL to apoptotic material.

CONCLUSION

In patients with SLE, a reduced functional activity of the MBL pathway of complement, in relation to expression of MBL variant alleles, is associated with increased levels of autoantibodies against cardiolipin and C1q, but not against MBL. We hypothesize that an enhanced production of autoantibodies may be related to disturbed clearance of apoptotic material due to impaired MBL function.

Opsonization with C1q and mannose-binding lectin targets apoptotic cells to dendritic cells

Deficiencies of early components of the classical complement pathway, particularly C1q, are strongly associated with susceptibility to systemic lupus erythematosus. Recent data link this predisposal to autoimmunity to an inappropriate clearance of apoptotic cells, which could lead to a loss of self-tolerance. In the present study, we demonstrate that opsonization of apoptotic cells with C1q and mannose-binding lectin allows and facilitates their uptake not only by macrophages but also by human immature dendritic cells (DCs). Both C1q and mannose-binding lectin enhance the uptake of apoptotic cells by DCs in a dose-dependent way. The uptake of C1q-opsonized apoptotic cells, but not nonopsonized apoptotic cells, by DCs stimulated the production of IL-6, IL-10, and TNF-alpha, without an effect on IL-12p70. We conclude that these recognition molecules of the complement system do not sequester apoptotic cells from DCs, but rather promote their uptake by immature DCs. Therefore, we propose that early complement components support safe clearance of cellular debris by facilitating phagocytosis and possibly by immunomodulatory mechanisms, thus preventing autoimmunity.

[Significance of serum anti-Clq Ab in evaluation of lupus nephritis activity and its curative effects of pharmacotherapy on lupus nephritis]

OBJECTIVE

To investigate the significance of serum anti-C1q Ab of evaluation of lupus nephritis activity and its curative effects of cyclophophamide therapy on lupus nephritis (LN).

METHODS

The level of serum anti-C1q antibody of 75 patients with LN was examined by enzyme-linked immunosorbent assay (ELISA) of the 75 patients the incipient cases had never received corticosteroid and immunosuppressant and the recurrent cases had stopped the immunosuppressant treatment for more than 3 months and were treated, if so, with prednisone with the dosage </= 10 mg/d. Thirty-one patients underwent renal biopsy. The patients underwent treatment of cyclophophamide. The relationships between serum anti-C1q Ab level and lupus nephritis activity, renal pathohistology, as well as laboratory parameters were analyzed, followed by further regular follow-up to investigate its influence to the curative effect.

RESULTS

Fifty-five of the 75 patients (73.3%) were anti-C1q Ab positive with the level of (92 U/ml +/- 41 U/ml). The mean time of conversion of urinary protein into negative was 9 months in the positive C1q positive group and 6 months in the C1q negative group. One year after, 25% of those with positive C1q antibody failed to convert into urinary protein negative, and 90% of those with negative C1q antibody converted into urinary protein negative. One year after, 32% of those whose serum C1q antibody remained positive 1 month after the treatment failed to convert into urinary protein negative, and 91% of those whose serum C1q antibody remained positive 1 month after the treatment converted into urinary protein negative. The serum anti-C1q Ab level was positively correlated with the lupus nephritis clinical active index, proteinuria, and titer of anti-dsDNA, and was negatively correlated with the levels of serum C3 and C4. Renal biopsies showed a positive correlation between the serum anti-C1q Ab level and the activity index of renal pathohistology. Multivariate analysis showed that the serum anti-C1q Ab level after treatment were associated with the curative effect and prognosis of LN.

CONCLUSION

Serum anti-C1q Ab is not only a good index of lupus nephritis activity, but also reflects renal involvement and curative effect. That serial measurement of serum anti-C1q Ab may provide better clinical strategies for the therapy.

Anti-C1q antibodies in nephritis: correlation between titres and renal disease activity and positive predictive value in systemic lupus erythematosus

OBJECTIVE

To investigate antibodies to complement 1q (anti-C1q) and investigate the correlation between anti-C1q titres and renal disease in systemic lupus erythematosus (SLE).

METHODS

151 SLE patients were studied. In patients with biopsy proven lupus nephritis (n = 77), activity of renal disease was categorised according to the BILAG renal score. Sera were tested for anti-C1q by enzyme immunoassay. Serum samples were randomly selected from 83 SLE patients who had no history of renal disease, and the positive and negative predictive value of the antibodies was studied.

RESULTS

Patients with active lupus nephritis (BILAG A or B) had a higher prevalence of anti-C1q than those with no renal disease (74% v 32%; relative risk (RR) = 2.3 (95% confidence interval, 1.6 to 3.3)) (p<0.0001). There was no significant difference in anti-C1q prevalence between SLE without nephritis and SLE with non-active nephritis (BILAG C or D) (32% v 53%, p = 0.06) or between active and non-active nephritis (74% v 53%, p = 0.06). Patients with nephritis had higher anti-C1q levels than those without nephritis (36.0 U/ml (range 4.9 to 401.0) v 7.3 U/ml (4.9 to 401.0)) (p<0.001). Anti-C1q were found in 33 of 83 patients (39%) without history of renal disease. Nine of the 33 patients with anti-C1q developed lupus nephritis. The median renal disease-free interval was nine months. One patient with positive anti-C1q was diagnosed as having hypocomplementaemic urticarial vasculitis syndrome during follow up.

CONCLUSIONS

Anti-C1q in SLE are associated with renal involvement. Monitoring anti-C1q and their titres in SLE patients could be important for predicting renal flares.

Interaction of C1q with the receptor calreticulin requires a conformational change in C1q

The interaction between C1q and the chaperone calreticulin was studied under various conditions. When both proteins were present in equal amounts in solution, no interaction could be demonstrated. However, C1q immobilized on a hydrophobic surface, exposed to heat-treatment or bound to immunoglobulins (Igs) showed a strong, rapid and specific binding of calreticulin. The interaction appeared to be a two-step process, and the initial phase of interaction was sensitive to high concentrations of salt but not to a physiological salt concentration. The following strong binding was insensitive to salt and extremes of pH but sensitive to strongly denaturing agents (urea and guanidine). The sensitivity to salt during the initial phase of interaction was practically identical to that observed when calreticulin was bound to type V collagen. Binding between C1q and calreticulin could be inhibited by serum amyloid P component and by proteinase K-digested ovalbumin, and the binding of calreticulin to proteinase K-digested ovalbumin was shown to be inhibited by C1q. The data indicate that C1q binds stably to the peptide-binding site of calreticulin and that the initial binding of calreticulin to C1q involves the collagen-like domain of the C1q molecule. In conclusion, our results suggest calreticulin as a potential receptor for an altered conformation of C1q as occurs during binding to Igs. Thus, the chaperone and protein-scavenging function of calreticulin may extend from the endoplasmic reticulum to the topologically equivalent cell surface, where it may contribute to the elimination of immune complexes and apoptotic cells.

Classical and alternative pathway complement activation are not required for reactive systemic AA amyloid deposition in mice

During induction of reactive systemic amyloid A protein (AA) amyloidosis in mice, either by chronic inflammation or by severe acute inflammation following injection of amyloid enhancing factor, the earliest deposits form in a perifollicular distribution in the spleen. Because the splenic follicular localization of immune complexes and of the scrapie agent are both complement dependent in mice, we investigated the possible complement dependence of AA amyloid deposition. In preliminary experiments, substantial depletion of circulating C3 by cobra venom factor had little effect on experimental amyloid deposition. More importantly, mice with targeted deletion of the genes for C1q or for both factor B and C2, and therefore unable to sustain activation, respectively, of either the classical complement pathway or both the classical and alternative pathways, showed amyloid deposition similar to wild type controls. Complement activation by either the classical or alternative pathways is thus not apparently necessary for the experimental induction of systemic AA amyloid in mice.

Mini-review: A pivotal role for innate immunity in the clearance of apoptotic cells

Apoptotic cells can be recognized and taken up by both macrophages and dendritic cells. Phagocytosis of apoptotic cells generally leads to active suppression of cytokine production by professional phagocytes. This is different from the response towards cells that die by necrosis, which induce a pro-inflammatory cytokine profile. Uptake of apoptotic cells involves a large number of receptors and opsonins, which bind to cellular ligands exposed during the various stages of apoptotic cell death. Among the opsonins of apoptotic cells, complement factors, including C1q, and complement-activating members of the pentraxin family play an important role. This is indicated by in vitro phagocytosis studies and supported by the susceptibility to systemic autoimmunity of carriers of genetic deficiencies for early complement proteins. The present review summarizes the role of molecules of innate immunity in the handling of apoptotic cells by macrophages and dendritic cells. It is proposed that C1q and other opsonins prevent autoimmunity and maintain self-tolerance by supporting the efficient clearance of apoptotic material, as well as by actively modulating phagocyte function.

Anti-C1q autoantibodies in murine lupus nephritis

Autoantibodies against C1q can be found in the circulation of patients with several autoimmune diseases including systemic lupus erythematosus (SLE). In SLE there is an association between the occurrence of these antibodies and renal involvement. How anti-C1q autoantibodies contribute to renal disease is currently unknown. Cohorts of MRL-lpr mice, which are known to develop age-dependent SLE-like disease, were used to study the relationship between levels of anti-C1q autoantibodies and renal disease. We collected serum, urine and renal tissue and analysed autoantibodies, complement levels and renal deposition as well as renal function. At 2 months of age all mice already had elevated levels of anti-C1q autoantibodies, and elution of kidneys revealed the presence of these antibodies in renal immune deposits in MRL-lpr mice and not in control MRL+/+ mice. In conclusion, anti-C1q antibodies are already present in serum and immune deposits of the kidney early in life and therefore can play a role in nephritis during experimental SLE-like disease in mice.

Complement activation in human prion disease

The central event in the neuropathological process of prion diseases (PrD) is the accumulation of abnormal prion protein accompanied by severe neuronal loss. Despite the infectious nature of these diseases, no prominent immune response has been detected yet. However, recent studies have shown that complement, a component of the innate immune system, is involved in the early pathogenesis of experimental prion infection. Here we demonstrate, in the diseased human brains, the presence of active compounds of the complement system, like C1q and C3b, in extracellular disease-associated prion protein deposits and the membrane attack complex in neurons. The neuronal localization of the membrane attack complex correlates well with the severity of disease-specific pathology and TUNEL labeling of neurons, irrespective of genotype or molecular phenotype of human prion diseases.

Natural IgM antibodies in sera from various animals but not the cat kill Toxoplasma gondii by activating the classical complement pathway

Sera from swine, rabbit, and dog, that had never been exposed to Toxoplasma gondii, demonstrated significant killing of T. gondii tachyzoites in vitro, while cat serum did not. Swine and rabbit sera contained natural IgM antibody against the tachyzoites, and the classical complement pathway was activated by the binding of natural IgM antibody to the tachyzoites, leading to lysis. Anti-T. gondii antibodies, induced in swine or cat infected with T. gondii, had no killing effect by themselves but killed the tachyzoites in the presence of swine complement. However, the anti-T. gondii antibodies of swine or cat demonstrated a very low killing effect in the presence of cat complement. This suggests that T. gondii tachyzoites have an evasion mechanism to prevent lysis which is specific for cat complement.

Neuronal localization of C1q in preclinical Alzheimer's disease

Complement has been postulated to contribute to inflammatory reactions associated with the neuropathology of Alzheimer's disease (AD). C1q, an initial component of the complement cascade, is associated with neuritic plaques and with neurons in the hippocampus of AD brain. Here, we report the presence of C1q in a cognitively intact subject, previously identified as preclinical AD. We compared in detail brain tissue of this preclinical case with a genetically related late-onset AD case. In the AD brain, C1q was typically associated with fibrillar Abeta plaques in frontal cortex and with plaques and neurons in the hippocampus. In the preclinical subject, C1q was abundantly present but it was cell-associated only, being primarily colocalized with neurons in both frontal cortex and hippocampus. However, no predominant cortical neuronal C1q localization was found in other preclinical cases or in Down's cases of different ages. Thus, it is possible that this neuronal-associated C1q reflects an early, but transient, response to injury that may modulate the progression of neurological dysfunction in AD.

Autoantibodies against mannose-binding lectin in systemic lupus erythematosus

In systemic lupus erythematosus (SLE), autoantibodies directed against complement components of the classical pathway, especially against C1q, are associated with severe disease and are of prognostic value for flares of lupus nephritis. Mannose-binding lectin (MBL), the recognition unit of the MBL pathway of complement activation, has structural similarities to C1q. Deficiencies of MBL have been shown to predispose to the development of SLE and to influence the course of the disease. We hypothesized that the presence of autoantibodies to MBL, analogous to autoantibodies to C1q in patients with SLE, may contribute to disease development. The occurrence of anti-MBL autoantibodies was assessed by enzyme-linked immunosorbent assay (ELISA) of 68 serum samples from 20 patients with SLE and in serum from 70 healthy controls. Levels of antibodies directed against MBL were significantly higher in patients with SLE compared to healthy subjects. No significant difference was found between patients with active disease compared to those with inactive disease. While the occurrence of anti-C1q autoantibodies was associated with renal involvement, no such relationship was found for anti-MBL autoantibodies. A significant correlation was found between anti-MBL and anti-C1q antibody levels. The level of anti-MBL antibodies was negatively correlated with MBL-complex activity of circulating MBL. Anti-MBL autoantibodies were of the immunoglobulin G (IgG) isotype and the binding site of IgG anti-MBL was located in the F(ab')2 portion. We conclude that anti-MBL are present in sera from SLE patients and influence the functional activity of MBL.

Localization of ligand-binding sites on human C1q globular head region using recombinant globular head fragments and single-chain antibodies

As a charge pattern recognition molecule, human C1q can bind a range of immunoglobulin and non-immunoglobulin ligands via its carboxy-terminal globular domain and activate the classical complement pathway. Each globular domain has a heterotrimeric organization, composed of the carboxy-terminal halves of one A (ghA), one B (ghB), and one C (ghC) chain. Recently, we have found that the recombinant forms of individual ghA, ghB and ghC bind differentially to IgG, IgM, gp41 peptide 601-613 of human immunodeficiency virus-1 (HIV-1), gp21 peptide 400-429 of human T cell lymphotrophic virus-I (HTLV-I), beta-amyloid peptide, and apoptotic cells, suggesting a modular organization of the globular domain. This paper examines the interaction of ghA, ghB and ghC with two known C1q ligands: Klebsiella pneumoniae porin OmpK36 and salivary agglutinin. In addition, we have used a panel of recombinant single-chain antibodies (scFv) specific for ghA, ghB and ghC in order to map sites on the heterotrimeric globular domain which are likely to interact with IgG1, IgG3, IgM, OmpK36, salivary agglutinin and gp41 loop peptide. The combined use of recombinant ghA, ghB, ghC and single-chain antibodies has revealed at least three ligand-binding sites on the globular domain of C1q: one is IgG- and OmpK36-specific, the second (IgM-binding site) is most likely overlapping with IgG/OmpK36 binding site, and the third (the gp41-binding site) seems to be located at the junction between the collagen and globular domains.

Human cord blood leukocyte innate immune responses to defense collagens

The innate immune system provides critical protection during initial infections before the generation of an appropriate adaptive (antibody or T cell mediated) immune response. These early defense mechanisms may be particularly critical for neonates in whom the adaptive immune system is not fully operational. Pattern recognition molecules target potential pathogens for destruction by the innate immune system, and likely facilitate the initiation of a pathogen-specific immune response. Defense collagens, such as C1q, MBL and SPA, comprise a family of such proteins that, via specific interactions with phagocytic cells, play a role in this first line of defense. To begin to assess the importance of these innate defense mechanisms in neonates, cord blood plasma and leukocytes were isolated, and responses to these components of the innate defense system were assessed. C1q enhanced the phagocytosis of targets suboptimally opsonized with either IgG or complement components, and this enhancement of phagocytosis was blocked by anti-CD93/C1qRP MAb by 57% to 68%. Flow cytometric analysis demonstrated that neonatal monocytes and neutrophils expressed CD93/C1qRP similarly to adult cells, with several-fold greater expression on monocytes than on neutrophils and essentially no expression on lymphocytes. Superoxide production in response to multivalent C1q by neonatal neutrophils was also comparable to adult cells. We also confirm that C1q and MBL are present in neonate circulation. Thus, the data demonstrate that these recognition and effector mechanisms of the innate system are functional in the newborn and similar to that of adult cells.

Diagnostic and prognostic significance of anti-C1q antibodies in systemic lupus erythematosus

PURPOSE OF REVIEW

The presence of a wide variety of autoantibodies is a characteristic finding in systemic lupus erythematosus. Autoantibodies against nuclear proteins, such as anti-nuclear and anti-double-stranded DNA antibodies, are used as diagnostic markers in systemic lupus erythematosus. Renal involvement is frequently found in systemic lupus erythematosus and is an important risk factor for death. Therefore, markers for the diagnosis and follow-up of nephritis are very important. Anti-C1q autoantibodies are strongly associated with renal involvement in systemic lupus erythematosus. This study will review recent findings on the pathogenic role and clinical importance of anti-C1q antibodies in lupus nephritis.

RECENT FINDINGS

Recent clinical studies have clearly emphasized the diagnostic relevance of anti-C1q autoantibody levels in patients with lupus nephritis. With a possible negative predictive value of 100%, anti-C1q autoantibodies are the only exclusive antibodies associated with the involvement of a single organ in systemic lupus erythematosus. Next to the clinical findings, the pathogenic significance of anti-C1q antibodies has been shown in an animal model. The deposition of autologous C1q in healthy glomeruli of mice after the infusion of anti-C1q antibodies induces moderate tissue damage.

SUMMARY

The latest insight into the pathogenesis of anti-C1q autoantibodies in the development of lupus nephritis and the recently demonstrated clinical importance of anti-C1q autoantibodies for the diagnosis of lupus nephritis support the value of further investigations. New diagnostic methods for the detection of anti-C1q and an accurate follow-up of antibody levels might be of use in clinical practice.

Anti-C1q antibodies and antiendothelial cell antibodies in systemic lupus erythematosus ? relationship with disease activity and renal involvement

The aim of this study was to investigate the relationship between the presence and titre of antibodies against C1q (anti-C1q Ab) and disease activity and renal involvement in patients with systemic lupus erythematosus (SLE). Anti-C1q Ab were measured in 79 patients with SLE (70 women and 9 men; mean age 41.7 years; mean disease duration 8.4 years): 19 patients had active disease with lupus nephritis, 8 active disease without nephritis, 26 inactive disease with nephritis and 26 inactive disease without nephritis. Anti-dsDNA antibodies (EIA and immunofluorescence), antiendothelial cell antibodies (AECA) and complement levels (C3, C4, total haemolytic complement activity) were determined in parallel. Anti-C1q Ab were positive in 49%, anti-dsDNA Ab in 61% and AECA in 19% of the patients, respectively. Significantly higher titres of anti-C1q Ab were found in patients with active disease compared with those with inactive SLE ( P < 0.01). Serum levels of anti-C1q Ab showed a positive correlation with anti-dsDNA Ab and SLEDAI score ( P < 0.01) and a negative correlation with C3 ( P < 0.05), C4 ( P < 0.01) and CH50U ( P < 0.01). The presence of anti-C1q Ab was not different between patients with or without nephritis. In patients with ( P < 0.05) and without nephritis ( P < 0.01) the frequency of anti-C1q Ab was significantly higher in active patients compared with inactive patients. Both anti-C1q and anti-ds-DNA Ab were detectable in 74% of patients with active nephritis but only in 30% of all other patients ( P=0.001). None of the patients with active nephritis was negative for anti-C1q and anti-dsDNA Ab, whereas 37% of the patients without active nephritis were negative for both antibodies ( P < 0.01). Sensitivity, specificity, positive and negative predictive values for active lupus nephritis among SLE patients were 100%, 50%, 51.9% and 100% for anti-dsDNA Ab (EIA) and 74%, 70%, 57% and 89.4% for positive findings of both anti-dsDNA and anti-C1q Ab. The presence and titre of anti-C1q-Ab in SLE are related to disease activity. Absence of anti-dsDNA Ab excludes active nephritis; positive findings of both anti-dsDNA Ab and anti-C1q Ab are of relatively high specificity for active nephritis.

Interaction of fucoidan with the proteins of the complement classical pathway

Fucoidan inhibits complement by mechanisms that so far remain to be unraveled, and the objective of this work was to delineate the mode of inhibition by this sulfated polysaccharide. For that purpose, low molecular weight fractions of algal (Ascophyllum nodosum) fucoidan containing the disaccharide unit [-->3)-alpha-L-Fuc(2SO3(-))-(1-->4)-alpha-L-Fuc(2,3diSO3(-))-(1-->](n) have been studied. Gel co-affinity electrophoresis and a new affinity capillary electrophoresis (ACE) method have been implemented to characterize fucoidan-complement protein complexes. Fucoidan binds C1q, likely to its collagen-like region through interactions involving lysine residues, and then prevents the association of the C1r(2)-C1s(2) subunit, required to form the fully active C1. In addition to C1q, fucoidan forms a complex with the protein C4 as observed by ACE. The fucoidan inhibits the first steps of the classical pathway activation that is of relevance in view of the proinflammatory effects of the subsequent products of the cascade. This study shows that a high level of inhibitory activity can be achieved with low molecular weight carbohydrate molecules and that the potential applicability of fucoidan oligosaccharides for therapeutic complement inhibition is worthy of consideration.

Antibody-mediated glomerulonephritis in mice: the role of endotoxin, complement and genetic background

Antibody-mediated glomerulonephritis in man may be exacerbated by infection and this effect may be mediated by bacterial endotoxin. There is evidence supporting a role for endotoxin in heterologous nephrotoxic nephritis in rats, but the role of endotoxin in this model in mice has not previously been explored. Previous data in mice on the role of complement in this model are conflicting and this may be due to the mixed genetic background of mice used in these studies. We used the model of heterologous nephrotoxic nephritis in mice and explored the role of endotoxin, complement and genetic background. In this study we show a synergy between antibody and endotoxin in causing a neutrophil influx. We also show that C1q-deficient mice have an increased susceptibility to glomerular inflammation but this is seen only on a mixed 129/Sv x C57BL/6 genetic background. On a C57BL/6 background we did not find any differences in disease susceptibility when wildtype, C1q, factor B or factor B/C2 deficient mice were compared. We also demonstrate that C57BL/6 mice are more susceptible to glomerular inflammation than 129/Sv mice. These results show that endotoxin is required in this model in mice, and that complement does not play a major role in glomerular inflammation in C57BL/6 mice. C1q may play a protective role in mixed-strain 129/Sv x C57BL/6 mice, but the data may also be explained by systematic bias in background genes, as there is a large difference in disease susceptibility between C57BL/6 and 129/Sv mice.

Bartter syndrome complicated by immune complex nephropathy. Case report and literature review

The unusual coincidence of Bartter syndrome and C1q nephropathy is described and the literature reviewed. An African-American girl presented at 4 years of age with acute hyponatremic dehydration and failure to thrive. Persistent hypokalemic alkalosis and secondary hyperaldosteronism were found. The case was atypical for Bartter syndrome in that proteinuria (0.19 g/day) was present. Renal biopsy showed juxtaglomerular hyperplasia and C1q nephropathy. Molecular analysis showed deletion of the renal chloride channel gene (CLCNKB) typical of autosomal recessive childhood Bartter syndrome. Chronic sodium and potassium chloride replacement therapy together with indomethacin normalized her metabolic status, and she experienced catch-up growth. Proteinuria persisted, however. This is the first documentation of C1q nephropathy, in mild form, complicating autosomal recessive Bartter syndrome. This case shows the importance of the renal biopsy and of molecular analysis in delineating the cause of atypical nephropathy associated with Bartter syndrome. These findings add to the evidence of a possible association between the congenital syndrome and acquired immune complex nephropathy.

[Complement-binding and immuno-modulating properties of polyreactive immunoglobulins]

New data concerning biological properties of polyreactive immunoglobulins (PRIG) were obtained as a result of treatment of mouse serum immunoglobulins by 4 M KSCN and are presented in the paper. In particular, the capacity of PRIG to bind C1q, the subunit of the first component of complement was studied. It was shown that PRIG's binding capacity to C1q is similar to that of intact immunoglobulins. Intravenous administration of PRIG into mice together with either sheep red blood cells or heat-inactivated staphylococcal bacteria did not affect the immune response to these antigens. Meanwhile, the same administration of PRIG together with the purified protein derivate of tuberculin resulted in 10-fold increase of mouse antibody response to PPD. These results demonstrate that PRIG can have some immuno-modulating properties concerning low-immunogenic antigens.

[Comparative effects of complement inhibitors in vitro and in vivo experiments: an immunoenzyme method in studying subcomponent C1q inhibition and complement inhibition in model animals]

Methods of analysis of inhibition of complement system in vitro and in vivo have been developed for study of effects of medical drugs on the complement. The first one, ELISA method, for determination of inhibition of the first stage of complement activation includes binding of C1q subcomponent to immunoglobulin. The second method is based on capacity of mink serum to kill mice at the intravenous administration due to the action of mink complement. The effects of heparin, known anticoagulant, and suramin, used for treatment of trypanosomiasis, have been studied using these systems. The inhibition constants of binding suramin and heparin binding evaluated by the first method C1q were 411 +/- 29 micrograms/ml (or 0.287 +/- 0.020 mumole/l) and 36.4 +/- 1.7 micrograms/ml (or 2.28 +/- 0.10 mmole/l), respectively. This indicates that heparin binding with C1q in 10 times is higher, than that for suramin (as weight ratio) or 100 times higher in molar ratio. Administration of 3 mg of suramin or 0.3 mg of heparin to mice protected them against lethal action of intravenously injected 0.08 ml of mink serum. Blood concentrations of these compounds approximately correspond to inhibition constants for C1q binding, obtained using in vitro method.

Human peritoneal macrophages in culture: a model for studying inflammatory disorders in vitro

In this study we characterized a model of human peritoneal macrophages maintained in culture for up to 48 h that can be used to study different functions of this cell population in vitro. The cells remained viable and functionally active over time, with well-preserved phagocytic properties. They expressed a macrophage marker, CD14. Once in culture, human peritoneal macrophages secreted C1q and nitric oxide in a pattern described in murine, guinea pig, and rat peritoneal macrophages. The described model can be used to study physiology and pathophysiology of peritoneal macrophages in vitro, offering all the advantages of the use of a human cell population.