Rabbit C1q: purification, functional and structural studies

Detection of hepatitis B antigen in circulating immune complexes in acute and chronic hepatitis

By using polyethylene glycol precipitation at low concentration (PEG test) and the radiolabeled C1q binding test, immune complexes were detected sera from acute (23/28) and chronic (28/32) hepatitis patients, hemodialyzed patients with chronic hepatitis B surface (HBs) antigenemia (7/19), and asymptomatic HBs antigen carriers (2/11). After treatment of PEG precipitates with acidic pH, heating, or proteolytic enzyme (protease), electroimmunodiffusion or radioimmunoassay revealed the presence of HBs antigen or antibody in dissociated immune complexes in sera from several acute and chronic hepatitis patients. Electron microscopy showed immune complexes of HB virus in 9 of 12 PEG precipitates obtained from PEG-test-positive sera; these 9 precipitates were from patients with acute or chronic hepatitis and the other three from chronic HBs Ag carriers. Free HB virus particles were observed after protease digestion of PEG precipitates. Neither immune complexes nor virus particles were seen in precipitates from PEG-test-negative but HBs-Ag-positive sera from chronic carriers.

Differential effect of the autoimmune Yaa and lpr genes on the acceleration of lupus-like syndrome in MRL/MpJ mice

The Yaa gene (Y chromosome-linked autoimmune acceleration), linked to the BXSB/MpJ Y chromosome, and the autosomal recessive lpr (lymphoproliferation) gene have been shown to accelerate the progression of the lupus-like autoimmune syndrome in the BXSB and MRL strains, respectively. To compare more directly the role of the Yaa and lpr genes in the development of the autoimmune syndrome, the Y chromosome of BXSB mice was transferred to MRL mice by backcross procedures, and the effect of the Yaa gene on the autoantibody formation and the development of lupus-like nephritis in MRL mice was investigated in comparison with those bearing the lpr mutation. The Yaa gene as well as the lpr gene were able to shorten the life span of MRL mice as a result of the accelerated development of lethal lupus-like nephritis. However, the acceleration promoted by the Yaa gene (50% mortality rate: 12 months) was less severe than that induced by the lpr gene (50% mortality rate: 7 months). This may be related to the finding that the lpr gene enhanced the production of a large spectrum of autoantibodies, including anti-DNA, rheumatoid factors and anti-gp70, and of cryoglobulins, whereas only anti-gp70 production among the autoantibodies studies was markedly enhanced by the Yaa gene. The selective autoimmune accelerating effect of the Yaa gene was similarly observed in (NZW X MRL)F1 hybrid mice. Our results suggest that the Yaa gene, unlike the lpr gene, exhibits selective autoimmune accelerating activity, but as a result of increased formation of certain nephritogenic autoantibodies such as anti-gp70 antibodies, the Yaa gene is able to accelerate the progression of lupus-like nephritis in lupus-prone mice.

Role of C1q in phagocytosis of Salmonella minnesota by pulmonary endothelial cells

The Re mutant of Salmonella minnesota adheres in much greater numbers than the wild type to endothelial cells derived from the bovine pulmonary artery. Since the Re mutant is distinguished from wild-type S. minnesota by its ability to bind C1q and since endothelial cells possess receptors for C1q, we examined the role of C1q in the phagocytosis of the S. minnesota Re mutant. First, preincubating endothelial cells with C1q-enriched medium resulted in increased adherence of the Re mutant (17.9 x 10(4) versus 6.6 x 10(4]. Second, preincubating the Re mutant with C1q-enriched medium resulted in increased numbers of adherent bacteria (62.1 x 10(4) versus 6.6 x 10(4]. Preincubation of both endothelial cells and bacteria with C1q-enriched medium resulted in increased adherence above control levels but less adherence than when either cells or bacteria were preincubated separately in C1q-enriched medium. If serum depleted of C1q was used for preincubation of endothelial cells or bacteria, adherence was reduced below control levels. Thus, C1q plays an important role in the initial steps (recognition, binding, and ingestion) of phagocytosis. Next, the role of C1q was investigated in the respiratory burst response. Levels of superoxide anion released from endothelial cells 15 min after phagocytosis of the Re mutant (100 bacteria per endothelial cell) were assayed by measurement of the superoxide dismutase-inhibitable reduction of ferricytochrome c. Superoxide anion release was increased during phagocytosis of the Re mutant (35 nmol of O2- per 3 x 10(6) endothelial cells) and was also elevated above control values by incubation with soluble C1q (10 nmol of O2- per 3 x 10(6) endothelial cells). These results indicate a role for C1q in both the ingestion and the response of endothelial cells to the S. minnesota Re mutant.

A substrate amplification system for enzyme-linked immunoassays. Demonstration of its general applicability to ELISA systems for detecting antibodies and immune complexes

Self recently described a substrate system for alkaline phosphatase (AP)-dependent ELISAs which markedly increased sensitivity, compared to using p-nitrophenyl phosphate. This increase is achieved by having AP, the primary enzyme, produce an activator for a secondary enzyme-substrate system, within which marked amplification occurs. We adapted this technique to study antibodies to casein, bovine serum albumin, ovalbumin, and cardiolipin in the sera of patients with systemic lupus erythematosus (SLE) and normal individuals. The new substrate system yielded titres 30-50-fold higher than those with p-nitrophenyl phosphate (Sigma 104, p-NPP). In addition, when used in a solid-phase C1q binding assay we were able to use a 1 : 100,000 dilution of AP-conjugated anti-human IgG with the amplified substrate, compared to the 1 : 1000 dilution needed with p-NPP. This system is extremely valuable because of its flexibility. It can either be very sparing of limited samples, or if the added sensitivity is not needed, 100-fold less AP conjugate may be used. Thus rare or expensive conjugates can be significantly conserved.

Antisperm antibodies and circulating immune complexes of vasectomized men with and without coronary events

We compared antisperm antibody and circulating immune complex (CIC) levels in serum samples from 101 vasectomized and 101 normal age-matched nonvasectomized men; 31 of each group had histories of coronary heart disease (CHD). Vasectomy and CHD status were treated as categorical independent variables in the two-way analysis of variance. Elevations of both systolic and diastolic blood pressures were significantly associated with age and body mass index but not vasectomy. Antisperm antibodies (immobilizing and agglutinating) were significantly associated with vasectomy (P less than or equal to .001); the incidences were similar in men with and without CHD. The CICs were significantly associated with vasectomy in a Staphylococcus aureus (FcSa) CIC assay (P less than or equal to .001) and a Raji cell CIC assay (P less than or equal to .05). A third CIC assay, the Clq binding assay, did not reveal a difference between any subgroups. Generally, CICs occurred more frequently in the CHD group by the FcSa assay and particularly the Raji cell assay (P less than or equal to .001). In summary, vasectomized men had a higher incidence and higher levels of circulating antisperm autoantibodies and CICs than did age-matched controls.

Severe hemolysis caused by antibodies against the mushroom Paxillus involutus and its therapy by plasma exchange

It has been shown that fatal "poisoning" with the mushroom species Paxillus involutus is caused by antibodies against the fungus in sensitized patients. Because circulating immune complexes play an important role, therapeutic procedures which can eliminate those complexes could stop immune hemolysis. A 37-year-old patient became severely ill after repeated ingestion of sufficiently cooked Paxillus involutus. As a result of hemolysis with reversible shock symptoms, acute renal failure developed. Plasma exchange with 3,000 ml albumin 5% was carried out daily during the first 3 days after admission. Each plasma exchange lowered free hemoglobin and immune complex levels by 60%-75%. Acute renal failure was successfully treated with hemodialysis. Specific IgG-antibodies against membrane particles of Paxillus involutus were detected by hemagglutination tests in the serum of the patient. The sequence of reactions resulting from the testing procedures strongly suggests the formation of immune complexes. These complexes are likely to bind to erythrocytes acting as innocent bystanders. Activation of the complement system finally results in hemolysis and shock. In addition to adequate shock treatment elimination of these immune complexes by plasma separation seems to be the therapy of choice.

Receptor-mediated binding of C1q on pulmonary endothelial cells

Normal undamaged pulmonary endothelial cells appear to be immunologically privileged in that they do not express receptors for the Fc portion of IgG nor for C3b. However, these receptors become unmasked on endothelial cells injured by viral infection or exposure to white cell lysates. We now present evidence to indicate that C1q binds to specific receptors on the surface of normal healthy endothelial cells. The binding is dose-dependent, reversible and saturable. Furthermore our data show that binding of C1q to endothelial cells is via the collagenous portion of the molecule not via the globular head regions. Thus binding of C1q to endothelium would have the effect of exposing Fc receptors that could then bind to IgG of circulating immune complexes. That Fc receptors are in fact exposed is shown by rosette formation with antibody sensitized erythrocytes. With 2C1r-2C1s-associated C1q, no binding occurred using C1 fixation and transfer assays. Our results indicate that C1q binding to endothelium provides a means for localizing immune complexes on pulmonary vessels and may be important in the initiation and progression of the inflammatory response.

Role of anti-pilus antibodies in host defense against gonococcal infection studied with monoclonal anti-pilus antibodies

Several monoclonal antibodies directed against gonococcal pili have been used to investigate the potential contribution of anti-pilus antibodies to host defense against gonococcal infection. Included were two antibodies (SM1 and SM2) which reacted with conserved determinants present on pili from all strains tested and others which exhibited antigenic specificity. Immunoblotting experiments revealed that antibodies SM1 and SM2 recognize epitopes on two different peptides derived by CNBr cleavage of alpha-pili from Neisseria gonorrhoeae P9-2. All antibodies used were capable of activating complement, as shown by their ability to bind Clq, and one type-specific antibody was effective in complement-mediated bactericidal killing. Antibodies directed against at least some pilus epitopes may therefore contribute to bactericidal activity during the course of natural infection. The opsonic effect of type-specific antibodies was demonstrated by their ability to stimulate luminol-dependent chemiluminescence of human polymorphonuclear leukocytes and promote phagocytic killing of variant P9-2. Phagocytic killing in the presence of each monoclonal antibody paralleled the increase in chemiluminescence, suggesting that for this variant killing was an inevitable consequence of the interaction of polymorphonuclear leukocytes with gonococci opsonized with anti-pilus antibodies. Antibody-mediated chemiluminescence of polymorphonuclear leukocytes was enhanced in the presence of human complement, and a weak opsonic effect was detected with one of the cross-reacting antibodies (SM1) when this system was used. Although cross-reacting antibody SM1 and type-specific antibody SM13 showed considerable differences in biological properties, they were of the same isotype and bound to native pili on intact gonococci in similar numbers and with similar avidity.

Effect of EDTA and citrate on the functional activity of the first component of complement, C1, and the C1q subcomponent

The first component of complement, C1, is a calcium-dependent complex of the three distinct subcomponents, C1q, C1r, and C1s. Earlier observations revealed that treatment of C1 with EDTA led to a loss of hemolytic C1 activity even after recalcification. Therefore, it was of interest to study whether EDTA has an additional effect on C1 and its subcomponents, beside its chelating capacity. The chelating effect of EDTA was compared to that of citrate. It was found that treatment of C1 or C1 with EDTA followed by addition of Ca++ led to a loss of hemolytic activity up to 90%, depending on EDTA concentration. Even pretreatment of EDTA with varying amounts of Ca++ did not prevent the inactivation of C1 or C1. In contrast, after dissociation of C1 or C1 by citrate, 100% of the original C1q activity is recoverable on addition of C1q deficient serum as source of C1r and C1s. EDTA-treated serum, however, showed a concentration-dependent loss of hemolytic C1q activity, indicating an inhibitory effect of EDTA on C1q. EDTA-treated C1q, fluid phase or bound to EA, was no longer able to form an hemolytically active C1 complex by interaction with C1r and C1s.

Rat Clq: isolation and purification from normal serum and development of a sensitive hemolytic assay

Rat Clq was isolated and purified from normal rat serum by a two-step procedure: affinity chromatography on a human IgG-Sepharose 4B column and Bio-Gel A 5m column chromatography. From 1.8 l of normal serum, the procedure yielded 4.5 mg of homogeneous and hemolytically active rat Clq as shown by three bands of peptide in SDS polyacrylamide gel electrophoresis under reducing conditions and by a single precipitin line between rat Clq and rabbit anti-rat Clq antibody. Rabbit anti-rat Clq antibody prepared by immunizing a rabbit with 225 micrograms of rat Clq was specific as shown by a single precipitin line between the antibody and normal rat serum and rat Clq with complete identity. The amino acid composition of rat Clq was very similar to that of human Clq. The purification procedure also yielded Clq-depleted rat serum which was used with the homogeneous Clq to establish a sensitive hemolytic assay: 4.5-13.5 ng of rat Clq can be reproducibly quantitated. The concentration of Clq in Brown Norway rats was estimated to be 41.5 +/- 3.0 micrograms/ml serum.

Effect of the C1q on the soluble collagen-platelet interaction

The mechanism by which C1q inhibited soluble collagen-induced platelet aggregation was examined. Platelet aggregation induced by soluble collagen in gel filtrated platelets was inhibited by the addition of C1q. There were no cross-reactions between C1q, purified soluble collagen receptor and both of their polyclonal antibodies in enzyme-linked immunosorbent assays. These results suggest that the effect of C1q on soluble collagen-induced platelet aggregation does not compete at the same binding site on the platelet surface.

Evaluation of circulating immune complexes in lymphomas and leukemias using two different assays

Circulating immune complexes (CICs) have been detected in the sera of patients with non-Hodgkin's lymphoma (NHL), Hodgkin's disease, chronic myeloid leukemia, and acute lymphoblastic leukemia by using C1q-binding and L1210-binding assays. Both assays gave broadly similar patterns of reactivity in terms of frequency and magnitude, though there are some differences. Significantly elevated CIC levels were observed in all pathologic groups. However, sera from NHL patients with an unfavorable prognosis consistently exhibited the highest frequency of positive values and mean CIC levels in both these assays. The two tests showed concordance in 66.6% of the NHL patients' sera and were significantly correlated. Of the sera from NHL patients 12.7% were positive in the C1q-binding assay only and 15.9% in the L1210-binding assay only. Both the assays gave positive results in some patients, and a degree of overlap indicates the presence of different types of CIC in cancer patients' sera. The combined use of two methods for detecting CICs may be useful for evaluation of the activity, the extent, and the prognosis of the malignant disease.

Enzyme-linked immunosorbent assay for C1q in human serum by use of monoclonal antibodies

A sandwich ELISA system has been developed for the detection of C1q in human serum. It is specific, uses monoclonal antibodies, is sensitive into the nanogram range and is rapidly performed. Therefore, it may be a helpful tool for clinical routine diagnosis, e.g., detecting abnormal C1q levels in patients with rheumatic disorders. Various combinations of poly- and monoclonal antibodies were tested in a sandwich assay. One of these combinations, in particular, resulted in a highly reproducible standard curve: C1q bound to solid-phase polyclonal anti-C1q was detected by the monoclonal antibody 242 G3. In this assay, the C1q concentration in sera of normal individuals was found to be 160 micrograms/ml (mean value of 70 normal human sera). This ELISA detected nanogram levels of C1q and gave results comparable to those obtained by haemolytic C1q titration. One nanogram of C1q corresponded to ca. 2.6 X 10(10) effective C1q molecules. With this technique, selective C1q deficient sera as well as sera from patients with rheumatoid diseases were analysed.

Comparison of pathologic and normal sera by immune complex determination: five disease groups within 190 samples are discriminated by computer-selected combinations of 13 methods. Report of the Italian committee for the study of immune complexes (WIC)

Pathological (190) and normal (33) sera were tested for their content of circulating immune complexes (CIC) by a battery of 13 assays performed in 11 laboratories. Statistical processing was done both by pooling all pathological samples and by extracting those falling into well-defined disease groups, i.e., rheumatoid arthritis, diabetes, lupus, melanoma, and glomerulonephritis. Highly significant correlations between methods--taken two at a time--for each disease differed in proportion (ranging from 6 to 30%) and in the pattern displayed on a checkerboard. Disease-linked patterns were also found when a function maximizing discrimination between pathological and normal samples was derived by combining the information from all methods. Here the order and the weight attributed by the computer to the methods differed for each of the disease groups. Taken together these results are interpreted as an indication that all assays may not determine the same classes of CIC, and thus vary in sensitivity depending on the prevailing properties of the complexes present in the serum, which in turn may depend on the etiology, pathogenesis, and stage of the disease.

Autoantibodies in juvenile arthritis

Sera from 104 children with JA with different onset-types of disease were evaluated for 19S IgM RF by the LFT , hidden 19S IgM RF by the hemolytic assay, ANA by HEp-2 cell substrate, and levels of IC by the C1qSPA . Their relationship to active disease was determined. Classical 19S IgM RF were detected by the LFT in only seven patients. All were late-onset polyarticular females. Hidden 19S IgM RF were detected by the hemolytic assay in the separated IgM-containing fraction in 55 patients of all onset-types. Clinical activity correlated with the presence of hidden 19S IgM RF in 82% of cases. ANA, using the HEp-2 cell substrate, were found in 61 patients, the majority showing a speckled, immunofluorescent pattern. ANA were noted in all RF positive patients and in nine of 10 patients with iridocyclitis. IC were found in 39 patients, and correlation with clinical activity occurred in 54% of cases. A search for positive associations among the four parameters showed no statistically significant correlations except for the concordance of ANA positivity in all seven RF positive patients. The presence of hidden RF correlated more closely with disease activity (P less than 0.001) than did that of ANA or IC. The significance of these data and previous studies remains to be determined. We have demonstrated that in the average JA population 7% have 19S IgM RF and about 60% have hidden RF, ANA, or elevated levels of IC. The present findings of 98 of 104 patients with at least one of the abnormal immunoproteins , the association of ANA in patients with iridocyclitis or with RF positivity, of hidden RF with disease activity, and the presence of 19S IgM RF in isolated IC suggest a possible immunologic etiology for JA.

Cutaneous vasculitis and immune complexes in severe bronchiectasis

Four patients with severe bronchiectasis (chronic bronchial suppuration) are described who developed cutaneous lesions associated with exacerbations of their respiratory disease. The skin abnormalities consisted of purpuric lesions in three patients and an erythematous vasculitis in one. Circulating immune complexes were present in all patients and in three skin biopsy specimens showed deposition of C3, IgG, and IgA in dermal blood vessels. Haemophilus influenzae had been isolated from the sputum of all four patients and in two patients was present at the time the cutaneous lesions appeared. It is suggested that local immune complex deposition was responsible for the skin lesions which occurred during acute exacerbations of bronchiectasis.

Human C1q: rapid isolation and quantitative determination by immunodiffusion

A simple and rapid 2-step procedure for isolating C1q from human plasma at high yields (about 50%) is described. The purification involves diaminopropane precipitation followed by chromatography on IgG-Sepharose. The final product (obtained at a concentration of about 1.5 mg/ml) was electrophoretically and immunochemically pure and stable at -70 degrees C for long periods. The Mancini technique for the quantitative determination of C1q was reinvestigated and the use of gels containing high salt concentrations (1.0 M NaCl) was found to be absolutely necessary. A value of 0.076 mg/ml C1q in pooled human plasma was obtained.

Hemodialysis leukopenia and complement function with different dialyzers

The relationship between leukopenia and the complement system during hemodialysis was re-examined by studying not only the in vivo effects of four different dialyzer membranes (cellulose hydrate, cuprophan, cellulose acetate, and polyacrilonitrile) on leukocyte counts and complement levels, but especially by investigating the effects of these membranes on complement function in vitro. Whereas from in vivo studies no definite conclusions could be drawn, in vitro investigations provided clear-cut information. When more sophisticated technical approaches were undertaken, it became evident that hemodialysis leukopenia has to be thought of in terms of chemotactic factor generation. In fact, a strict correlation was demonstrated between the degree of leukopenia induced by the dialyzers tested and the ability of the relative membrane to generate chemotactic activity in vitro. Moreover, the previously observed ability of polyacrilonitrile membrane to induce a decrement in complement function was due to the ability of polyacrilonitrile to adsorb complement activity and did not correspond to effective complement consumption. This finding explained why polyacrilonitrile dialysis is not accompanied by a decrease in circulating granulocytes. Taken together, our data strongly point to a pivotal role of complement system in the pathogenesis of hemodialysis leukopenia.

Circulating immune complexes in haemophilia and von Willebrand's disease

Sera from 63 patients with haemophilia A, 21 with haemophilia B and 29 with von Willebrand's disease were screened for the presence of circulating immune complexes (CICs), serological markers of hepatitis A and B virus, autoantibodies and factor VIII or factor IX inhibitors. CICs were detected by the 125J Clq binding assay (ClqBA), the solid phase conglutinin assay (KgBSP) and the solid phase Clq assay (ClqSP). The incidence of CICs detected by the ClqBA and the ClqSP methods in haemophiliacs and in von Willebrand patients was higher than that observed in normal subjects, while the prevalence of CICs detected by the KgBSP method was not. The presence of CICs was not correlated with patient age, severity of disease, presence of hepatitis B virus serological markers, abnormal liver function tests or factor VIII inhibitors. A significant connection was demonstrated between CICs detected by the ClqBA method and replacement therapy when the dose administered over 1 year was over 20 000 U of factor VIII or IX concentrates. The high proportion of CICs in von Willebrand's disease, not connected with the replacement therapy or the presence of serological markers of hepatitis virus, is in agreement with the possibility that immune complexes may be related to the disease itself and independent, at least in part, of exogenous agents.

An enzyme-linked immunoassay for circulating immune complexes using solid phased goat Clq

An ELISA procedure was developed for measuring circulating immune complexes (IC), using solid phased goat Clq. The use of purified Clq from this species significantly diminished the background uptake of the enzyme-labeled goat antibodies used in the assay, in comparison with Clq isolated from human, guinea pig or rabbit serum. The test specimen results are reported as micrograms equivalent (microgram eq)/ml of heat aggregated human immunoglobulin G (HAIgG), and are based on standard curves developed with this latter reagent for each assay. The 2 World Health Organization (WHO) reference preparations for immune complex determinations (HAIgG and a human tetanus antitoxin-toxoid immune complex) were assayed by this ELISA procedure, and the results obtained were in very good agreement with the WHO established values. All the reagents in the ELISA, including the lyophilized HAIgG standard and the solid phased Clq are stable for more than one year at 4 degrees C. The range of accurate quantitation in test serum is 2-500 micrograms/ml, when using a 1:100 specimen dilution. The total incubation is less than 2 h, with no preliminary preparation of test specimens. The average concentration of IC reactivity in 126 healthy adults was 6 micrograms eq/ml, and the normal upper limit was determined to be 12 micrograms eq/ml.

Limitations of immune complex measurements in colorectal disease

Three techniques (Clq, Raji and L1210 binding assays) alleged to measure circulating immune complexes (ICs) were applied to the sera of 101 patients with colorectal disease (54 carcinoma; 23 inflammatory; 13 benign tumour and 11 miscellaneous) at the time of diagnostic or definitive surgery, and 58 healthy adult controls. Elevated levels in the pathological sera were observed by all 3 methods in order of sensitivity: Raji greater than Clq greater than L1210. However, none of them differentiated between benign, inflammatory and neoplastic conditions nor, in the case of colorectal carcinoma, was there any correlation with stage of disease. With the exception of Raji v. L1210 (r = 0.43, P less than 0.001), correlations between the various assays were poor and levels of serum carcinoembryonic antigen (CEA) did not correlate with ICs measured by any of the techniques. Indeed, the IC assays were even less discriminatory than CEA, which was elevated mainly in the serum of carcinoma patients and which was positively correlated with serum gamma-glutamyl transpeptidase (gamma GT) (r = 0.42, P less than 0.005). The data suggest that the lack of concordance between the IC assays is a reflection of heterogeneity among ICs, interfering factors present in pathological sera, or both. Thus the IC assays deployed here have neither diagnostic nor prognostic utility in colorectal disease at this time, and immunochemical characterization of the serum reactive material detected by the different assays is required.

Adoptive T cell immunotherapy of MSV-induced tumours in nude mice. Part II. Sequential analysis of serum immune complexes and blocking activity in reconstituted mice in relation to tumour biology

In seven separate experiments, nude (nu/nu) mice carrying established murine sarcoma virus (MSV) tumours were reconstituted with syngeneic (+/+) immune splenic T cells. These immune protected mice were randomly divided to provide smaller groups for serial exsanguination. At various time points mice were individually bled and CIC concentration and blocking activity of each individual serum was determined. Control sera were obtained from nu/nu and adult +/+ mice inoculated with tumour cells only, and from nu/nu mice protected with normal +/+ spleen cells. In all the mice studied, CIC and blocking appeared to be mutually independent parameters throughout the MSV tumour course. On the other hand, in immune protected mice considered alone or together with the control groups, CIC and time after tumour cell inoculation, but not tumour size, were significantly correlated. A significant relationship between blocking and tumour size was also established, although this only applied to immune protected mice. However, analysis of the combined data from sequentially bled immune protected mice in relation to different phases of tumour behaviour, did not support the notion that blocking, and more particularly the persistence of CIC, contribute to tumour regrowth and dissemination.

Critical aspects of immune complex assays employing polyethylene glycol

Treatment of artificial immune complexes (ICs) with 2.5% polyethylene glycol (PEG)--conditions under which C1q-binding activity is routinely measured in the fluid phase--produced marked changes in molecular size as determined by Sepharose 6B chromatography. The effect of PEG on the C1q-binding capacity of ICs, was therefore investigated using a solid phase (SP) system. PEG enhanced the binding of aggregated human gammaglobulin (AHG) and artificial ICs to SP-C1q and, in reverse experiments, also increased the binding of C1q to SP-AHG. The degree of enhancement varied according to the Ag:Ab ratio employed; the binding of ICs formed in moderate Ab excess was only modestly enhanced but that of complexes formed at slight Ab excess, equivalence and Ag excess was markedly elevated. The profile of PEG-induced enhancement of binding paralleled that of similar ICs in the C1q fluid phase system, suggesting that C1q binding in the latter may be influenced by PEG. However, the C1q-binding activity of in vivo-formed ICs seemed to be relatively unaffected by PEG since enhanced binding was comparable in control and pathological sera. The results indicate that PEG causes cross-linking and aggregation of ICs (and possibly other serum proteins) which may alter their biological activity and hence influence the results of IC assays that employ this agent.

An enzymatically active antigen-antibody probe to measure circulating immune complexes. II. E. coli beta-galactosidase in the probe and C1q as the recognition unit

An enzymatically active probe (beta-galactosidase-anti-beta-galactosidase complex) is used to measure circulating immune complexes (CIC), in a competition assay where probe and CIC are confronted with a 'recognition unit'. The latter is bovine conglutinin in the original description of this method. Here we describe a version utilizing human or bovine C1q. The two techniques are compared for their sensitivity and specificity, on both in vitro formed tetanus toxoid-anti-toxoid complexes and on sera from patients with selected diseases. The results confirm that the two recognition units are sensitive to families of CIC that only partially overlap. The parallel use of conglutinin and C1q yields both quantitative and qualitative information on the nature of CIC in individual sera.

Immune tolerance and atherosclerosis in rabbits. Effect of high-fat and cholesterol-supplemented diets

Breeding rabbits were fed diets supplemented with 5% milk or soya protein for 1 month before conception and throughout pregnancy and lactation. Four groups of 5 or 6 of their offspring were given high-energy isonitrogenous diets containing either 30% soya or milk protein. Half of the animals from each litter received the same protein as their dams; the remainder were fed the alternative (i.e. dams soya; offspring milk, and vice versa). 0.75% cholesterol was added to the diets between 30 and 120 days after weaning. Animals given the same protein as their dams formed substantially lower amounts of food antigen-specific antibody than rabbits fed a novel protein at weaning but the extent of aortic atherosclerosis was similar in all groups. In a second experiment groups of 5-8 weanling rabbits were fed a cholesterol-free diet containing 30% soya and 17% saturated fat for 1 year. Animals in group 1 were bred from dams given soya but those in groups 2 and 3 were derived from a colony fed a soya-free diet. Rabbits in group 3 were immunised by repeated parenteral injections of soya protein and developed high levels of antisoya antibodies. Group 1 and 2 animals were injected with saline only but antisoya antibodies were substantially higher in animals derived from the soya-free breeding colony. Although serum cholesterol and triglyceride levels were similar in all groups, animals from dams fed soya (group 1) had significantly less aortic atherosclerosis (10% involvement of ascending aorta) than those reared from a colony fed a soya-free diet (group 2; 32%). Parenteral immunization with soya protein (group 3) was not associated with significantly increased atherosclerosis (37%). These findings indicate that perinatal exposure to dietary antigen in rabbits may be important in modulating the systemic immune reaction to food antigens. The magnitude of this systemic response is unlikely to alter the nature or distribution of cholesterol-induced atherosclerosis but may have an important influence on the development of aortic disease produced by prolonged feeding of high-fat, cholesterol-free diets.

The functions of endogenous C1q, a subcomponent of the first component of complement, as a receptor on the membrane of macrophages

C1q, the Fc-recognizing subcomponent of the first component of complement is synthesized by peritoneal macrophages. During the secretion phase C1q serves as an Fc-binding protein in the membrane of macrophages. The Fc-mediated rosette formation was inhibited in a dose-dependent manner when macrophages were pretreated with anti-C1q F(ab')2, whereas C3b rosette formation was not affected. Furthermore, preincubation of peritoneal macrophages with anti-C1q F(ab')2 abolished, dose- and time-dependently, the polyanion-mediated stimulation of secretion of lysosomal enzymes. Polyanion-induced enzyme release was prevented after incubation of polyanions with highly purified C1q. The inhibition of Fc receptor activity by polyanions (i.e. dextran sulfate, liquoid, polyvinyl sulfate) is completely reversed upon treatment of these macrophages with protamine. These findings are compatible with the hypothesis that C1q produced by macrophages serves in the macrophage membrane as an endogenous receptor for Fc and polyanionic molecules. Thus, C1q mediates cell-bound biological receptor functions before it is released from these cells and is incorporated into the macromolecular C1 complex.

C1q binding and Raji immune complex assays: a comparison using defined immunoglobulin aggregates

Aggregated IgG is frequently employed as a standard in systems for the measurement of immune complexes in man and animals. In this paper aggregates prepared by heat or alkali denaturation of human IgG were fractionated by column chromatography through LKB AcA 22 Ultrogel. Heat aggregation yields preparations containing considerably more monomer than alkali treatment (47% and 6.3% respectively). The bulk of aggregated material prepared by both methods was of size 19 S or greater. Smaller aggregates were present in assayable quantities only in the alkali aggregated material. The sized fractions of aggregates IgG were tested in the presence of a human complement source for their efficiency in the C1q binding and Raji radioimmunoassay for immune complexes. Both techniques efficiently measured large aggregates (greater than or equal to 19 S) but the C1q binding assay measured smaller material with greater efficiency than did the Raji cell assay. Neither technique detected monomeric IgG. The date presented is relevant to the binding characteristics of the 2 assay systems studied and suggests that when used together they are capable of measuring immune complexes present over a wide range of sizes.

The use of TNP-conjugated polyacrylamide beads in a C1q binding inhibition test for circulating immune complexes

A new assay for the detection of circulating immune complexes is described. It is based on the same principle as the C1q deviation test: the binding of radiolabelled C1q to a solid phase is inhibited by immune complexes. Trinitrophenylated polyacrylamide beads are used as a stable C1q-reactive solid phase in our test. Aggregated IgG in normal serum could be detected by this method to a minimum concentration of about 10 microgram/ml. The test was used to quantitate circulating immune complexes in sera of patients with glomerulonephritis, liver diseases, lymphoma, and myeloid leukemia. The results are compared and correlated with those obtained by the C1q binding assay for the same sera.

Circulating immune complexes in human acute leukaemia

Circulating immune complexes (CIC) in the sera of 60 newly diagnosed leukaemic patients were investigated by two methods, 125I-C1q binding test (C1q-BA) and conglutinin binding assay (KgB-SP). Positivity percentages were respectively 20.0% (C1q-BA) and 28.3% (KgB-SP). The small overlap between the results of the two methods suggests the occurrence of different types of CIC. The presence of CIC was found to be related only to clinical haemorrhage and thrombocytopenia; it did not prove to affect the prognosis and the survival of leukaemic patient.

Non-specific immune responses in CBA/N mice infected with Trypanosoma brucei

CBA/N mice carry a genetic defect which causes a maturational arrest of normal B lymphocyte development, and results in an inability to mount IgM antibody responses against certain T lymphocyte-independent antigens. These mice were found to survive an experimental infection with Trypanosoma brucei two to three times longer than conventional mice. This enhanced survival does not appear to be related to the level of infection of the host since parasitaemias were similar in all strains tested. In addition, the level of non-specific polyclonal B cell activation as assessed by the enumeration of anti-TNP antibody-producing cells in the spleens of infected animals was found to be similar in CBA/N, CBA/CaT6 and A/J mice. In contrast, the level of circulating immune complex-like material was lower in CBA/N mice at a time when mice of other strains were dying from the effects of the infection. Finally, although CBA/N mice survive a T. brucei infection for a longer time interval, they exhibit a non-specific immunosuppression similar to that seen in conventional mice.

Antibody-independent binding of the first component of complement (C1) and its subcomponent C1q to the S and R forms of Salmonella minnesota

Strong bactericidal effects of normal guinea pig and human sera against the Salmonella minnesota S form and an R form (Re) depend on Ca2+, complement component C4, and subcomponent C1q of complement component C1. Therefore, the interaction of C1 and C1q with these forms was investigated. The bacteria directly bound subcomponent C1q, as demonstrated by fixation and transfer tests and by fluorescent methods. Binding of macromolecular C1 was shown by fixation and transfer tests and by C4 consumption. C1 fixation and transfer tests provide evidence that C1 and C1q were bound more tightly to the Re form than to the S form. At physiological ionic strength, all cell-bound molecules were released from the S form, whereas at least 60% remained on the cell surface of the Re form. The Re form showed another binding behavior for C1: preincubation of bacteria with purified C1q totally prevented C1 uptake by the S form, compared to only 10% inhibition of the uptake by the Re form. Therefore, we conclude that macromolecular C1 is bound differently by the S form than by the Re form. The analysis of five other core-deficient mutants of S. minnesota (Ra, Rb, Rc, Rd1, and Rd2) revealed that the difference could be explained by a deficiency of the O-specific polysaccharide. In contrast, all the C1q bound to Ra, Rb, and Rc mutants was detectable by the transfer test. Therefore, we postulate that binding of macromolecular C1 to these mutants must be due to an additional C1 subcomponent besides C1q.

Purification and characterization of subcomponent C1q of the first component of mouse complement

1. Mouse C1q, a subcomponent of the first component of complement, has been purified in a highly haemolytically active form by a combination of precipitation with EGTA, ion-exchange chromatography and gel filtration. Yields ranged from 3 to 5 mg/200 ml of serum, and the activity of final preparations was in the range of 2 X 10(13)-4 X 10(13) C1q effective molecules/mg. 2. The molecular weight of mouse C1q was 439 500 +/- 1586, as determined by polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulphate. 3. Mouse C1q was shown to be composed of non-covalently linked subunits, all being in the molecular-weight range 45 000-46 000, and three covalently linked chains each having a molecular weight of approx. 23 000 as determined on polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulphate by using non-covalently and covalently linked subunits of human C1q as markers with known molecular weights calculated theoretically previously [Porter & Reid (1978) Nature (London) 275, 699-704]. 4. Mouse C1q contained hydroxyproline, hydroxylysine, a high percentage of glycine and approx. 9% carbohydrate. The absorption coefficient and nitrogen content of C1q were also determined.

Fibronectin associated with Clq in a Clq isolation procedure

The complement component Clq, prepared by euglobulin precipitation of serum to which EDTA or EGTA had been added, contained fibronectin (FN) as detected by radioimmunoassay and immunodiffusion methods. The FN contents of the Clq preparations varied between 3 and 29% by weight of the Clq contents. Adsorptions of sera with polymerized IgG (an absorbent for Clq) in the presence or absence of EDTA removed all detectable Clq and between 12 and 95% of the FN. In a similar manner, adsorptions of sera and Clq preparations with insolubilized gelatin (to which FN will bind) reduced greatly or removed completely the FN component but also strikingly reduced the Clq contents. High salt concentration or the addition of EDTA did not alter the gelatin absorption results indicating that the association was not sensitive to high ionic condition and that Clq was equally bound as Clq or as the Cl complex. The results suggest that FN and Clq bind individually to both gelatin and IgG or that FN and Clq co-associate, accounting for removal of one component when the other is bound to its expected adsorbent.

Isolation and purification of human C1q from plasma

C1q was purified to homogeneity from human plasma by a 3-step purification procedure. Plasma was euglobulin precipitated, and the redissolved precipitate chromatographed on a rabbit IgG-Sepharose column. The 1 M NaCl buffer eluate was passed directly through a rabbit anti-human IgG-Sepharose affinity column. C1q freed of IgG was present in the flow through. The rationale for this scheme to remove IgG free and that bound to C1q is discussed. Overall recovery of C1q was about 40% with IgG less than 4 microgram/mg C1q. In SDS-polyacrylamide electrophoresis with non-reducing conditions bands at 52,000 and 42,000 daltons were demonstrated while with reducing conditions bands at 26,000, 24,000 and 20,000 daltons were found as reported by others. C1q was found to be stable at 4 degrees C for 1 year in a 1 M NaCl, 0.4 M Tris, 10% sucrose, 0.005 M EDTA, 0.02% NaN3, pH 8.6 buffer.

Quantitation of extracts containing tumour angiogenesis factor (TAF) by radioimmunometric and radioimmunoassays

An antiserum which is able to inhibit TAF-induced neovascularization in vivo (TAF antiserum) was used to develop two quantitative assays for TAF-containing tumour extracts (tumor TAF). 1) Radioimmunometric assay (RIMA): the IgG of the TAF antiserum was labelled with 125I. An excess of 125I-IgG was incubated with increasing concentrations of tumour TAF and the antigen-bound fraction was precipitated by addition of Clq. 2) Radioimmunoassay (RIA): an excess of iodinated antigen (tumour TAF) was incubated with TAF antiserum diluted so that binding in the absence of unlabelled antigen represented 70-80% of the maximum binding. When tumour TAF was added, competition between labelled and unlabelled antigen for the TAF antibody binding sites resulted in displacement of the former by increasing concentrations of the latter. A second antibody was used to precipitate the bound labelled antigen. Of the two assays, the RIMA was the more sensitive and, due to the lack of a purified antigen, allowed standardization of the results in a more accurate manner. Our data show that there was a good correlation between the ability of tumour TAF to induce angiogenesis in vivo and the degree of antiserum binding detected in vitro by both assays. Preparations containing TAF, whatever the source (i.e. human or animal tumours or tissue culture) shared common antigenic determinants. It is suggested that the quantitative assays should prove valuable in determining the clinical relevance of TAF as a tumour marker.

Circulating immune complexes in patients with lung neoplasms

A search was made for circulating immune complexes in 42 patients with biopsy-proven lung cancer; sex- and age-matched healthy volunteers were used as normal controls. Two different mthods were employed: Clq--binding assay and the conglutinin-binding test. Patients and controls were also examined for delayed hypersensitivity by a skin testing using a set of recall antigens. A significant difference was found in the incidence of immune complexes and the response to skin tests between neoplastic subjects and normal controls. However, the incidence of immune complexes was not related to delayed hypersensitivity or the other clinical features investigated.

Correlation of elevated C1q binding activity and carcinoembryonic antigen levels with clinical features and prognosis in bronchogenic carcinoma

The presence of immune complexes and carcinoembryonic antigen (CEA) was investigated in 50 patients with bronchogenic carcinoma at the time of and/or following diagnostic or definitive surgery. Immune complexes were measured by the C1q binding test and CEA by the Z gel method and elevations defined as values in excess of 2 S.D. above the normal mean, greater than or equal to 9.2% for C1q binding activity (C1q-BA) and greater than or equal to 5.0 ng/ml for CEA. The overall incidence of elevated values was 30.7% for C1q-BA and 34.2% for CEA. There was a greater incidence of elevated values of C1q-BA among patients with clinically evident disease. The differences with respect to CEA elevation were not significant due to the fact that 6 of 9 samples with elevated CEA values obtained from patients with no evident disease were in fact associated with the presence of clinically undetectable disease in these patients. Elevation of C1q-BA and CEA beyond the immediate postoperative period was predictive of a significantly shorter median survival time. The most significant differences in survival time were seen between patients with normal values for C1q-BA and CEA and those with elevations of one or both parameters, 6.0 vs. 19.5 months (p less than 0.001). Elevation of either parameter during the immediate pre- and postoperative period was not predictive of a poor survival. In terms of clinical application, it appears that CEA estimation had the best predictive value but that the addition of C1q-BA measurement may provide additional prognostic information, particularly in patients who do not have elevated CEA values.

Idiopathic rapidly progressive glomerulonephritis with C3 nephritic factor and hypocomplementemia

A 7-year-old boy with mild renal failure and signs and symptoms of acute poststreptococcal glomerulonephritis including severe hypocomplementemia had, by renal biopsy, numerous crescents but no deposits in the glomerular capillary loops. Instead, deposits identical in location and composition to those described for children with idiopathic rapidly progressive glomerulonephritis were present. The severe hypocomplementemia was found to be due to high levels of C3 nephritic factor; niether nephritic factor nor hypocomplementemia has been reported in rapidly progressive glomerulonephritis of the idiopathic type. Following prompt therapy with methylprednisolone intravenously, serologic abnormalities disappeared and renal function greatly improved, but a later biopsy showed 50% of the glomeruli obliterated by scarring. The case is of importance not only in indicating that severe hypocomplementemia does not rule out idiopathic rapidly progressive glomerulonephritis but also in adding to the list of diseases in which nephritic factor can be found.