Complement breakdown products in plasma from patients with systemic lupus erythematosus and patients with membranoproliferative or other glomerulonephritis

Influence of C3 level on the determination of C3d in plasma and synovial fluid by radial immunodiffusion

The influence of C3 levels on the determination of C3d in plasma and synovial fluid by radial immunodiffusion was investigated. In the method used, C3 is precipitated by 11% polyethylene glycol (PEG), and C3d is measured in the supernatant. In 51 healthy donors, a weak though significant correlation between C3 and C3d levels was found. The mean concentration of C3d was 1.6% of that in aged serum from healthy donors. So, small amounts of C3 (i.e., 1-2% of the normal plasma level) in the 11% PEG supernatants may contribute significantly to the C3d levels measured. A radioimmunoassay that detects C3, C3b, iC3b and C3c was used to measure C3 levels in the PEG supernatants. In PEG supernatants of 4 plasma samples, 0.3-0.6% of the C3 level in normal plasma was found, whereas in those of 2 synovial fluids much higher levels were found (4-10% of the normal plasma level). When purified 125I-labeled antibodies against C3c were added to the gel of the radial immunodiffusion, C3c antigen was detected in the precipitation rings obtained with all PEG supernatants of plasma samples from patients. Therefore, the quantitative contribution of C3 to the precipitation rings in the C3d radial immunodiffusion was analyzed after the addition of an excess of anti-C3c antibodies to the gel. No effect on the size of the C3d-precipitation rings obtained with plasma samples from patients was observed. However, the C3d precipitation rings obtained with synovial fluids were significantly smaller when the gel used in the radial immunodiffusion contained an excess of anti-C3c antibodies together with the anti-C3d serum. We conclude that it is necessary to add an excess of anti-C3c antibodies to the gel used for the radial immunodiffusion, for the determination of C3d levels in synovial fluid. An antiserum against human C3b, which contains both anti-C3c and anti-C3d antibodies, can be used for this purpose.

[A new case of bronchospasm under extracorporeal circulation]

A case of bronchospasm occurring after the termination of cardiopulmonary bypass is reported. The complement fractions C3a, C4a and C5a were measured before and right after CPB. Complement activation is not specific to CPB but may occur in any thoracotomy. The statistically significant increase in complement C3a without any pulmonary symptomatology has been reported by several authors. Complement activation cannot therefore be considered as the explanation of this bronchospasm.

Absence of IgA nephropathy in patients with ankylosing spondylitis

In 40 patients with ankylosing spondylitis (AS) no evidence for IgA nephropathy was obtained. This conclusion was based on the absence of hematuria and on the inability to find an increased incidence of IgA-containing immunoglobulin deposits in skin biopsies. Increased Clq binding assay was only found in those AS patients with anterior uveitis. In 26% of the skin biopsies perivascular mononuclear cell infiltrates were observed, and immunoglobulin deposits were seen in 65%. These facts suggest that the immunologic system is involved in the pathogenesis of this disease.

Prognostic and pathogenetic implications of immune complexes in human cancer

The dynamic relationships of circulating immune complexes (CIC) and associated immune reactants to stage of disease and prognosis in cancer patients have been evaluated for malignant melanoma. Patients were divided into group I patients, with no evidence of disease at sample time; group II patients, with minimal tumor burden; and group III patients, with advanced metastatic disease. By means of single- and serial-sample determinations, we have demonstrated correlation of CIC concentration, size, and composition to tumor burden, disease progression, and high risk of disease recurrence. In view of the phenotypic heterogeneity of antigen expression in malignant melanoma, we have extracted, purified, and utilized melanoma-associated antigens (MAA) from CIC, and human oncofetal antigens (HOFA) from fetal liver cells, and reacted them with patients' sera in an in vitro model that simulates tumor burden changes. The observed changes in CIC concentration and lattice size upon reaction with MAA and HOFA demonstrated a significant (p less than or equal to 0.001) relationship to patients' in vivo tumor burden, as well as to the origin of serum and antigen involved. Our results suggest a homeostasis of CIC size and concentration to associated antibodies and antigens operational in malignant melanoma patients' sera. In addition, we have demonstrated how the monitoring of more than one immune reactant, characterization of CIC size and composition, and evaluation of resulting reequilibrium caused by in vitro addition of antigen or antibody, could allow for an improved assessment of humoral immunity and its related pathogenetic effects in cancer patients.

CR1 deficiency in SLE: acquired or genetic?

Erythrocytes from 30 patients suffering from systemic lupus erythematosus (SLE) were tested for CR1 activity by an immune adherence haemagglutination technique. Defective CR1 activity (CR1D) was found in 11 (37%) of the patients on initial testing. On repeat testings, however, CR1 activity often varied from time to time and was shown to be inversely related to serum anti-DNA binding and apparent complement activation in vivo. Two of the 19 patients with normal CR1 activity acquired CR1D during the study. One patient with previously defective CR1 attained normal activity in the course of the study. The increased occurrence of CR1D in patients with SLE is largely or wholly acquired rather than genetically determined.

The quantitation of C3d by routine methods after the direct absorption of human plasma with anti-C3c

The immunological methods for quantitating C3d in plasma require first the removal of less fragmented intermediates as well as the intact C3. We describe an alternative method for the quantitation of C3d in human plasma. The components which should be removed are absorbed (precipitated) directly in the plasma by a specific anti-C3c antiserum. It is then possible to determine the concentration of C3d by routine immunological methods.

Defective host defence mechanisms in a family with hypocalciuric hypercalcaemia and coexisting interstitial lung disease

An extensive in vitro investigation of the host defence system was performed in 11 sibs of a large kindred with unexplained combination of familial hypocalciuric hypercalcaemia (FHH), interstitial lung disease and increased susceptibility to respiratory infections. The impairment of host defence mechanism was most likely related to granulocyte dysfunction. A severe myeloperoxidase deficiency was the most consistent granulocyte defect (P less than 0.001) and it was associated with a relatively diminished chemiluminescence (P less than 0.001). Moreover, a significantly diminished antistaphylococcal phagocytic (P less than 0.001) and killing (P less than 0.001) activity was found which in the absence of any opsonizing defect implicates an intrinsic granulocyte dysfunction. We found no abnormalities in number of B and T lymphocytes nor in the balance between helper and suppressor cells determined with monoclonal antibodies. Despite the recurrent infections no elevations of the immunoglobulin subclasses were found. The relationship between the inherited FHH, interstitial lung disease and susceptibility to respiratory infections remains obscure. It is, however, clear that impairment of the host defence might contribute to a decreased life expectancy in this family.

Monoclonal antibodies against complement 3 neoantigens for detection of immune complexes and complement activation. Relationship between immune complex levels, state of C3, and numbers of receptors for C3b

C3-bearing immune complexes and C3 activation products were detected by using two monoclonal antibodies, one specific for a neoantigenic determinant on C3c and the other for C3d. To quantitate immune complexes, the anti-C3c or anti-C3d antibodies were fixed to microtiter plates and reacted with test plasma. The binding of C3-bearing immune complexes in this plasma was then measured with radioisotope- or enzyme-labeled anti-human IgG. To test for C3 breakdown products, solid-phase monoclonal antibody to the C3d neoantigen was reacted with EDTA-plasma samples, and fixed iC3b or C3d was measured with a polyclonal anti-C3 antibody. Patients with autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, and Sjogren's syndrome, and paracoccidioidomycosis were found to contain immune complexes bearing C3b/iC3b or C3d. In most conditions, there were more C3d-containing immune complexes than C3b/iC3b. Although CR1 (C3b receptors) rapidly converted immune complex-bound iC3b to C3dg/C3d and lupus patients had reduced CR1, no correlation between the state of C3 on circulating immune complexes or levels of immune complexes and CR1 numbers was seen. However, levels of C3-fixing ICs correlated with levels of C3 activation products. This assay system with monoclonal antibodies to neoantigens expressed on activated, but not native, C3 provides sensitive and specific means for detecting and classifying C3-fixing immune complexes and for assessing C3 activation.

Genetically determined low C4: a predisposing factor to autoimmune chronic active hepatitis

Of 26 patients with autoimmune chronic active hepatitis (CAH) starting in childhood 18 (69%) had low C4 and 5 (19%) had low C3 serum levels. Impaired hepatic synthesis and immune-consumption were unlikely since transferrin levels were normal in all patients, albumin levels were persistently low in only 3, and only 3 had raised levels of activation fragment C3d. C4d was normal in all patients studied. In the families of 12 probands with low C4, 7 parents had low C4 and 2 had levels which were at the lower limit of normal. 5 of 10 siblings from 5 families had low C4. These results suggest that low C4 levels in CAH are genetically determined. C4 phenotyping in 20 patients and in 26 parents showed that 90% and 81%, respectively, had null allotypes at either the C4A or C4B locus compared with 59% in controls, indicating that defective expression of structural genes may contribute to the observed C4 deficiency.

Quantification of the C3d split products of human complement by a sensitive enzyme-linked immunosorbent assay

A double-antibody biotin-avidin enzyme-linked immunosorbent assay (ELISA) for quantification of the C3d split products is described. Polyethylene glycol 6000 was used to precipitate large C3 molecules, and the C3d-containing supernatant was used in the assay. C3d was measured in ethylenediaminetetraacetic acid plasma from 40 healthy blood donors, and the normal range was defined. Twenty-two patients were tested, and 12 of these had increased levels of C3d. No correlation was observed between total C3 and C3d in these patients. There was a close correlation between C3d measured by this method and by the double-decker rocket immunoelectrophoresis method. The C3d ELISA method is very sensitive, easy to perform, and time-saving and economical compared with most C3d methods already described. A procedure to define the lower detection limit and examine the reliability of an ELISA method in general is discussed.

Immunoglobulins and complement components in human aortic atherosclerotic intima

Concentration and preferential retention of immunoglobulins and complement components were studied in comparison with other plasma proteins in 42 human aortae with atherosclerosis. Saline and acid extracted IgG, IgA, IgM, C1q, C3c, C4, C9, C3A, C-reactive protein, alpha 1-antitrypsin, alpha 2-macroglobulin, albumin, transferrin and fibrinogen were quantitatively determined using the radial immunodiffusion. The fibrous plaques and their adjacent areas contained higher levels of each protein than intima with only fatty streaks. No significant differences were found between the fibrous plaques and their adjacent areas presenting intimal thickenings. Saline eluted IgG and IgA were significantly higher in the fibrous plaque intima than in intimal samples with fatty streaks and were the only proteins detected in the acid eluates. The complement components were present in all saline eluates, while C-reactive protein was found in 23 samples. Crossed immunoelectrophoretic studies showed the activation of saline C3 and C4. In 8 cases serum levels of the studied proteins were compared with their concentration in saline eluates obtained from intima and media. The immunoglobulins and complement components presented higher intima/serum and lower media/intima retention ratios than the other studied proteins suggesting their preferential retention in the intima. The presence of immune related proteins in the atherosclerotic intima and their preferential retention might be explained not only by an altered permeability but also in relation to their function.

Complement activation after myocardial infarction

Complement activation as reflected by C3, C4, and C3d levels was studied in 56 patients following myocardial infarction, 13 with the postmyocardial infarction syndrome (PMIS); 12 with prolonged postinfarction pyrexia; six with clinical evidence of pulmonary embolism; and 25 control patients without apparent complications. In most patients, C3d levels were elevated during the first ten postinfarction days and at the time of any pulmonary embolism; this probably represented local nonimmunologic complement utilization. The PMIS patients had much higher C3d levels associated with significantly lower concentrations of C3 at the time of disease activity. It is suggested that heart reactive antibodies combine with circulating cardiac antigens to form soluble immune complexes, and in the PMIS, these may become deposited in various sites resulting in complement-mediated tissue damage. The high C3d levels associated with the PMIS may also be of value in differentiating this condition from pulmonary embolism, as both problems may have similar clinical and roentgenographic features.

Sequential studies of complement activation in systemic lupus erythematosus

C1 and C3 activation, measured as C1r-C1s-C1 inactivator C1s-C1r-C1IA complexes in serum and circulating C3d were studied in serial samples from 33 patients with SLE. All patients demonstrated exacerbations during observation periods of 10-30 months and were divided into groups according to principal clincal features (mild SLE, severe extra-renal SLE, and lupus glomerulonephritis). Increased C1 activation was consistently found during exacerbation. C3d in plasma was a feature associated with severe disease flares. Activation of C1, but not of C3, was documented before flare-ups of disease activity, but such predictive information was mostly restricted to patients with extra-renal disease. C2 cleavage in plasma, studied serially in a few patients, appeared to be closely associated with C1 activation. Circulating immune complexes, measured with solid-phase C1q assay, did not always increase before development of clinical manifestations. Remission of symptoms was paralleled by decreasing concentrations of C1r-C1s-C1IA and of, when present, C3d. Similar findings were made for immune complexes but only in severe disease. Persisting C3d was observed in 3 patients, who subsequently developed renal failure. C1q levels were transiently low during flare-ups of lupus glomerulonephritis, but otherwise the concentrations of C1q, C4 and C3 did not show consistent patterns of variation in relation to disease activity.

Immunonephelometric quantitation of complement split product (C3d) plasma levels in rheumatic disease

A simple method is described for routine quantitative determination of C3d by laser nephelometry after precipitation of intact C3 by polyethylene glycol. Plasmas from 292 patients with different types of rheumatic disease was tested. Elevated C3d levels were a far more common finding than low levels of complement components C3 or C4, but despite the increased sensitivity, the test only seemed diagnostically useful for systemic lupus erythematosus and MCTD. Though a better test than the quantitation of C3 and C4, the value of C3d determination in rheumatic disease seems to be limited.

Correlation of disease activity with circulating immune complexes (C1qbA) and complement breakdown products (C3D) in patients with systemic lupus erythematosus. A prospective study

Most biologic effects of immune complexes are mediated through the activation of the complement system. The relationship between lupus disease activity and the presence of C3 breakdown products (C3d) and circulating immune complexes (CIC) as demonstrated with the C1q binding assay (C1qbA), was evaluated. Nearly all 13 systemic lupus erythematosus (SLE) patients had a stable disease course in this prospective study, nevertheless, in each patient the profiles of the serologic parameters were quite different. Despite the small number of investigated patients (13), it is concluded that irrespective of the disease activity, the serologic parameters could be either positive or negative. No relationship could be obtained between disease activity and the presence of C3d and/or CIC. Nor was there any evidence that the presence of CIC would indicate increased levels of C3 breakdown products (C3d). This observation argues against a pathogenetic significance of CIC detected by the C1qbA in SLE. In conclusion, the supposed link between the presence of CIC, consumption and activation of the complement system, and the activity of SLE needs further study.

Evaluation of plasma C3d and immune complex determinations in the assessment of disease activity of patients with rheumatoid arthritis, systemic lupus erythematosus, and spondylitis ancylopoetica

Patients with rheumatoid arthritis, systemic lupus erythematosus, and spondylitis ancylopoetica were examined, along with healthy controls, for C3d plasma levels, circulating immune complexes, C3 serum levels, and CRP. Immune complexes were determined using a Clq binding assay, a 2.75% PEG precipitation technique, including the analysis of IgG and C3, and a new laser nephelometric latex test. C3d plasma levels were significantly (P less than 1%) elevated in all groups of patients as compared to controls. With regard to the demonstration of circulating immune complexes, the PEG precipitation method discriminated best between patients and the control population. It was not possible to differentiate between the different disease entities with neither C3d serum levels or immune complexes. Concerning the assessment of disease activity, none of the evaluated parameters alone appears to be of clinical relevance. The individual application of more than one immune complex assay in combination with the measurement of C3d serum levels must be recommended if disease activity is to be assessed.

Plasma C3d/C3 quotient as a parameter for in vivo complement activation

Plasma levels of C3 and C3d in 30 healthy donors and 58 patients with systemic lupus erythematosus were determined by rocket immunoelectrophoresis and Con-A affinoimmunoelectrophoresis. Significantly decreased levels of C3 were found in approximately 50% of the SLE sera. Slight increases of free C3d were found in 55%, and marked increases in 9% of the SLE sera; the remaining SLE sera did not show increased C3d levels. When results were expressed as quotients of plasma C3d/C3, a significant pattern emerged and 70% of the SLE sera clearly fell outside the normal range. 10% of the SLE sera had normal C3d/C3 indices but had markedly depressed C3 levels. We conclude that in cases where total serum C3 is not markedly reduced (less than 60% of normal), the C3d/C3 quotient may be a more sensitive parameter for assessing in vivo complement activation than C3 or C3d determinations alone.

A simple method for quantitative measurement of C3d in human plasma

We describe a simple and reliable method for quantitating C3d in human plasma. The method rests on the finding that native C3 and its activation/inactivation product C3c bind to Concanavalin A, whereas C3d does not. Rocket affinoimmunoelectrophoresis with Con-A Sepharose incorporated into an intermediate gel permits quantitation of free C3d in 2-20 microliters aliquots of EDTA-plasma without any manipulation prior to sample application. Using this method, we found that the level of circulating C3d in plasma of 30 healthy donors was usually well below 3% of maximally convertable C3d.

Pathways to complement activation during cardiopulmonary bypass

Complement activation was assessed in 34 patients undergoing cardiopulmonary bypass. Arterial concentrations of complement fragments Ba and C3d rose in all patients, the increase in Ba preceding that of C3d. At the same time as complement fragments were being generated the arterial neutrophil count fell. These findings suggest (a) that complement activation is initiated by the alternative pathway during cardiopulmonary bypass and (b) that complement activation mediates loss of neutrophils during bypass. Complement mediated loss of neutrophils during the analogous setting of haemodialysis is the result of leucosequestration in the pulmonary vasculature. During cardiopulmonary bypass the lungs are out of circuit, so that activated leucocytes may sequester in other target organs. This may be an aetiological factor in the multi-organ failure occasionally seen after uneventful cardiopulmonary bypass.

Magnitude of bacteremia and complement activation during Neisseria meningitidis infection: study of two co-primary cases with different clinical presentations

Two co-primary cases of schoolchildren with acute meningococcal disease due to infection with Neisseria meningitidis serogroup B are described. The first patient presented with septic shock and purpura fulminans, bacteremia greater than 10(5) organisms/ml blood, low C3 and factor B levels and an elevated level of C3d. The second patient had meningitis, negative blood cultures, normal levels of serum complement components but more than 10(4) organisms/ml in CSF. A comparison of the quantitative bacteriology data and complement profiles for these patients suggests that the degree of activation of complement during meningococcemia is directly related to the number of organisms in the blood. This association may determine the different clinical syndromes.

Immunopathological correlation between mesangial C3d-deposition and C3d-fixing circulating immune complexes in lupus nephritis

By a direct immunofluorescent technique, glomerular C3d deposition was examined in a total of 50 renal biopsy specimens from patients with lupus nephritis. C3d deposition was then compared with disease activity, glomerular IgG and C3c deposition, and the levels of circulating immune complexes (CIC) measured by a solid-phase anti-C3d assay. There was a good correlation between disease activity and the positivity of glomerular C3d deposits (P less than 0.001), as well as C3c deposits (P less than 0.001). Even in clinically inactive patients, a relatively high percentage (59%) of C3d deposits were positive compared with C3c deposits (17%). Mesangial C3d deposition correlated with clinical disease activity more significantly (P less than 0.005) than capillary wall C3d deposition (P less than 0.025). C3d deposits were detected in all of the 30 cases with positive C3c deposits, and moreover, in 15 of the 20 (75%) cases with negative C3c deposits. Glomerular IgG deposits were almost always associated with C3d deposits, both in mesangial areas and along capillary walls, with statistical significance (P less than 0.005, P less than 0.001, respectively). The serum levels of C3d-fixing immune complexes (IC) were significantly correlated with the positivity and intensity of mesangial C3d deposits. This study demonstrates glomerular deposition of C3d in patients with lupus nephritis and reveals a significant correlation between mesangial C3d deposition and disease activity.

Plasma fibronectin and complement in surgical patients

Plasma fibronectin and a fragment of the third component of complement (C3b) are both opsonins of the reticulo-endothelial system. Twenty patients undergoing uncomplicated gastro-intestinal surgery were studied. There was a significant reduction in plasma fibronectin and total haemolytic complement, but not C3, in the early postoperative period (days 1 to 3). In six surgical patients critically ill with severe sepsis both plasma fibronectin concentrations and C3 concentration were reduced significantly when compared with the early postoperative period of uncomplicated surgery. In addition, in the critically ill patients, direct evidence of complement activation was demonstrated. These studies show a transient reduction of humoral host defence mechanisms following surgery which may be permissive to bacteraemia and complement activation.

The influence of polyethylene glycol precipitation and of ageing plasma and serum on the measurement of C3dg/d

In plasma and serum samples, ageing results in excessive C3dg/d values when measured by electroimmunoassay. The use of polyethylene glycol, either in the preparation of the samples or in the electrophoretic gels, gives falsely low values.

Circulating immune complexes and complement breakdown product C3d in glomerulonephritis and kidney transplantation

Circulating immune complexes (CIC) and the complement breakdown product C3d were measured in 81 patients with glomerulonephritis (GN), 28 patients with early and 25 patients with long-term renal transplants. CIC were measured by a Clq-binding assay and C3d by a double-decker rocket immunoelectrophoresis. In patients with GN, CIC were detected in 19 and elevated C3d levels found in 45 patients. The highest levels of C3d were found in patients with membranoproliferative GN type I and II, diffuse sclerosing GN and GN secondary to SLE and Wegener's granulomatosis. No relationship was found between CIC and C3d, and the combination of CIC with C3d measurements did not help to characterize 'nephritogenic' CIC. C3d was frequently elevated in patients with impaired renal function which may reflect an inflammatory 'nephritic' process, but may also be due to a reduced renal elimination. Furthermore C3d was frequently elevated in patients with improving or decreasing renal function, and in patients with heavy proteinuria. Longitudinal studies of renal transplant patients suggested that immunosuppressive treatment decreased the C3d level. Patients with early renal transplants had elevated C3d levels that normalized during the first month after successful transplantation. CIC and elevated C3d were not related to onset of acute rejection episodes in early transplant patients nor to late renal graft failure.

Polyclonal B cell activation, circulating immune complexes and autoimmunity in human american visceral leishmaniasis

In a prospective study, serum and plasma samples from 17 patients with kala-azar were collected in Rio de Janeiro. High levels of immune complexes (IC) were detected in serum by means of 125I-Clq and conglutinin binding assays. The Clq binding material had a sedimentation coefficient of 19-25S, as determined by ultracentrifugation on sucrose gradient. Plasma levels of C3 and C3 breakdown products were measured and the C3d levels were increased in six out of 11 patients. The occurrence of polyclonal B cell activation was suggested by (a) a marked increase of serum IgG and IgM levels and (b) of the presence of antibodies against various proteins and haptens (SRBC, DNP-BSA, FITC-BSA,KLH). There was a close association between the presence of IC and anti-immunoglobulin antibodies. Anti-smooth muscle antibodies were also observed. These data are consistent with a major role of polyclonal B cell activation in the induction of IC during visceral leishmaniasis.

Immunologic and biochemical studies on a patient with pyoderma gangrenosum

A patient with pyoderma gangrenosum without associated disease was studied. Routine investigations showed several abnormalities. High ESR, high alkaline phosphatase and glutamyl transferase (gamma-GT) levels, low iron and iron binding capacity, altered protein spectrum, presence of Staphylococcus aureus and group G hemolytic streptococci in ulcer culture, higher than normal antistreptolysin titers in the serum, and perivascular infiltration in the skin. Biochemical investigations aimed at finding any excessive hydrolytic activity did not reveal the presence of neutral proteases in circulation leaked out from PMN-leukocytes or elsewhere. Lysozyme levels were higher than normal, amylase and lipase levels were normal and 5' nucleotidase levels were below normal range. TCA-soluble polypeptides were present in the serum at levels two times higher than those in normal individuals. Immunochemical investigations showed the absence of immune complexes in the serum but presence of high amounts of C-reactive protein. Total complement activity was higher than normal and so was C3c level. Clq, C4, and C3d levels were within normal range. Biologic studies showed the presence of a factor in patient serum that made guinea pig skin hard, painful, erythematous, and eventually hairless, but not necrotic. A similar factor was either absent in normal serum or present in very low concentration. After salazopyrine treatment, all the above mentioned abnormalities corrected except that 5' nucleotidase activity remained slightly lower than normal, alkaline phosphatase levels remained slightly higher than normal, and C-reactive protein levels remained very high, though lower than those during intense disease activity.

Complement activating cryoglobulins in the nephritis of systemic lupus erythematosus

Complement activation in vitro by cryoglobulins isolated from the sera of 28 patients with systemic lupus erythematosus (SLE) was examined by incubating the cryoglobulin with normal human serum and performing crossed-immunoelectrophoresis of the mixture to detect C3 conversion. Eighteen of the 28 SLE cryoglobulins activated complement; eight by the classical pathway, four by the alternative pathway exclusively, and six by both pathways. In contrast only two out of 20 cryoglobulins isolated from the sera of normal subjects activated complement and both did so by the classical pathway. Twenty-three of the 28 SLE sera activated complement and complement activating cryoglobulins were isolated from 15 of these 23 sera. The parent sera of cryoglobulins activating complement had lower C4 and C3 concentrations than sera whose cryoglobulins did not split complement but these differences were not significant. The ability of SLE cryoglobulins to activate complement in vitro suggests that these immune complexes activate complement in vivo and thus may contribute to tissue damage in this disease. The activation of both classical and alternative complement pathways is in keeping with other evidence that both pathways are involved in SLE.

The third complement factor (C3) and its in vivo cleavage products: interaction with lectins and precipitation with polyethylene glycol

Five molecular forms of C3 expressing D but not C epitopes were identified following in vivo activation of the complement system. Examination of concanavalin A (Con-A) reactivity in crossed immunoelectrophoresis revealed that native C3, C3c and the beta mobile form 4 of C3d were completely precipitated by 100 micrograms Con A/cm2. The alpha-1 mobile form 1 of C3d did not interact with Con A, whereas the alpha-2 mobile forms 2 and 3 were retarded in electrophoretic migration by Con A. Native C3, C3c, and forms 4 and 5 of C3d were precipitated by 12% (w/v) polyethylene glycol (PEG). Form 1 of C3d was soluble in these PEG concentrations, whereas forms 2 and 3 were partially precipitated.

Lack of activation of C1, despite circulating immune complexes detected by two C1q methods, in patients with rheumatoid arthritis

The activation of C1 by circulating immune complexes in patients with rheumatoid arthritis was investigated. C1rC1s(C1-In)2 complexes in EDTA-plasma, reflecting C1 activation in vivo, were slightly raised in 35 of 57 patients with rheumatoid arthritis, though most patients had elevated levels of circulating immune complexes as measured with either the 125I-C1q binding test or the C1q solid phase assay. The activation of C1 by circulating immune complexes in vitro was investigated by measuring the generation of C1rC1s(C1-In)2 complexes during 60 minutes at 37 degrees C in diluted recalcified EDTA-plasma. In 16 of the 57 patients, a slightly increased C1 activation in vitro was observed. These patients tended to have high levels of circulating immune complexes. However, the majority of the patients with high levels of circulating immune complexes showed a normal C1 activation in vitro. Therefore, it was concluded that measurement of circulating immune complexes by either of the two C1q methods in patients with rheumatoid arthritis does not imply that these circulating immune complexes are able to activate C1.

Development and clinical application of electroimmunoassays for the direct quantification of the complement C3 split products C3c and C3d

The present report describes the development of electroimmunoassays for the direct quantification of C3d and C3c, split products of the third complement factor (C3). Both methods were developed as rocket immunoelectrophoreses, using two antibody preparations with specificities against the C and D epitopes on C3. A stable calibrator preparation for C3c and C3d was produced by autolytic cleavage of C3. Investigations of patients with anaphylactic reactions or chronic immunological disorders showed that quantification of C3c and C3d in plasma by these methods reflected the degree and rate of complement activation. C3d determination was found to be the most sensitive and reliable indicator of C activation, both during acute and chronic activation since C3c is eliminated considerably faster from the circulation than C3d (estimated half lives of 2 h and 4 h, respectively). Treatment of rheumatoid arthritis patients with prednisolone caused a prompt decrease of plasma C3d values, indicating that the clinical effect may be due to inhibition of complement activation.

Complement activation during cardiopulmonary bypass: quantitative study of effects of methylprednisolone and pulsatile flow

Forty four patients undergoing open heart surgery were divided into three groups. Group 1 (17 patients) underwent routine anaesthesia and surgery; group 2 (17 patients) received two doses of methylprednisolone (30 mg/kg), one during induction of anaesthesia and the other immediately before induction of cardiopulmonary bypass; and group 3 (10 patients) received pulsatile flow while undergoing pulsatile perfusion by the heart-lung machine. A modification of the previously described technique was used to detect and measure complement activation in plasma before and during the bypass period using crossed immunoelectrophoresis. About 45% of all patients showed measurable complement activation (greater than 4.5%) during cardiopulmonary bypass and the mean activation in this group was 6.4%. There was no significant difference between the three groups in complement activation. In group 2, however, women showed significantly more complement activation than men (p less than 0.05). It is suggested that neither corticosteroids nor pulsatile flow affect complement activation, but caution should be exercised in women receiving methylprednisolone.

The use of C3d as a means of monitoring clinical activity in systemic lupus erythematosus and rheumatoid arthritis

Plasma samples from 44 patients with systemic lupus erythematosus (SLE) and 43 with rheumatoid arthritis (RA) were assayed for C3d, a breakdown product of the third component of complement (C3), which was also measured in parallel. Levels of C3d varied in direct proportion with disease activity in RA, whereas C3 showed little change. Although C3d values also increased with worsening clinical condition in SLE, this trend was not considered to be sufficiently clear to be useful and did not provide any advantage over the routinely performed C3 assay.

The in vivo metabolism of C3 in human glomerulonephritis and after renal transplantation

Metabolic investigations of complement component C3 have been performed to study pathogenetic mechanisms in patients with glomerulonephritis and after renal transplantation. Purified and biologically active 125I-labelled C3 was given intravenously together with 131I-albumin to nine patients with different forms of glomerulonephritis and nine allograft recipients at different stages after renal transplantation. Control studies were performed in 16 normal individuals. The fractional catabolic rate (FCR) of the proteins was calculated with the metabolic clearance method (U/P ratio) and/or by analysis of the plasma radioactivity disappearance curve. An increased FCR of C3 was found in three patients with glomerulonephritis. A modestly elevated FCR of C3 was found in all but one of the transplant patients as calculated by the U/P ratio, while the FCR was high in only two when calculated from plasma radioactivity disappearance. Slight increases of C3 catabolism were found during two suspected rejection episodes, but may have been due to a general increase in protein turnover. The serum level of C3 was reduced in two recipients and in one of these the FCR of the protein was elevated. The remaining patients had normal or increased C3 levels. Judged from these results, activation of complement was only of modest importance in the patients studied.

Clinical application of a new nephelometric technique to measure complement activation

A new nephelometric technique to measure C3d as an indicator of complement activation, is described. C3d is isolated at high concentration of polyethyleneglycol (PEG), incubated with commercially available anti-C3d antiserum at a final concentration of 2.5% PEG and then measured in a Behring Laser Nephelometer. In contrast to previously available techniques our assay detects the low concentrations of C3d present in all normal subjects, which result from the continuous C3 catabolism occurring in vivo. We have also measured C3d blood concentrations in a large number of patients with diseases associated with complement activation. Raised C3d concentrations were found in 68% of rheumatoid arthritis, 57% of primary biliary cirrhosis, 38% of chronic active hepatitis, 100% of Gram-negative bacteraemia and 100% of malaria. The nephelometric technique has proved to be sensitive, economical and fast, and could be adapted for routine determination of C3d blood concentrations to monitor disease activity and response to treatment.

Partial myeloperoxidase deficiency in preleukemia

In seven subjects with partial and apparently acquired form of myeloperoxidase (MPO) deficiency, some functional properties of neutrophils (PMNs) were studied. Five patients suffered from preleukemia, one from diabetes mellitus and one from carcinoma of the breast with bone marrow metastases. Intracellular bactericidal activity, oxygen consumption and superoxide radical production were within normal limits. In three patients with preleukemia, the serum opsonic activity was markedly reduced (less than m-3SD) in an autologous system, but normal in the presence of pooled normal serum. Decreased opsonic activity was also found when these patient's sera were assayed in the presence of normal PMNs. Since the levels of IgG and C3 were comparable in the patients' sera and the pooled serum, a deficiency of another unknown opsonin or the presence of an opsonization inhibitor has to be postulated. The partial MPO defect apparently doesn't decrease the intracellular killing of Staphylococcus aureus by PMNs. The known susceptibility to bacterial infections in preleukemia may be explained by the reduction of serum opsonization conducing to a secondary decrease of the ingestion and killing of bacteria by the PMNs.

A single step immunoelectrophoresis method for the quantitation of complement C3c in biological fluids

An intermediate gel rocket immunoelectrophoresis (IRI) suitable for direct quantitation of complement split products with C3c specificity is described. The technique represents a simple, quick, and reproducible method for the assessment of complement activity in biological fluids in diseases. The advantages of the quantitative approach of the IRI method as compared to the conventional crossed immunoelectrophoresis (CIE) are the increased sensitivity, specificity, and precision of the method; also, the assay capacity is superior to CIE. The IRI-C3c assay is therefore highly suitable as a scientific tool, and may also be useful for routine laboratory investigations.

Plasma histamine concentrations and complement activation during house dust mite-provoked bronchial obstructive reactions

Lung function and histamine levels in peripheral venous plasma samples were followed after challenge with house dust mite allergen. In eight patients the mean maximal histamine concentration showed a significant rise during the early obstructive reaction when compared with the concentrations at similar time intervals after inhalation of a control solution. In nine other patients treatment with disodium cromoglycate (DSCG) caused a significant fall in plasma histamine concentrations indicating that histamine liberation plays a role during the early obstructive reaction and was released from the lung compartment. Histamine during early obstructive reactions compared with the pre-inhalation values did show a rise in mean maximal histamine concentration (1.5-4.1 ng/ml) but this was statistically not significant. During the late reaction neither significant increase in histamine nor inhibition by DSCG was found. Measurement of complement degradation products did not support the role of complement activation during either early or late bronchial obstructive reactions.

Low serum C4 concentrations: an inherited predisposition to insulin dependent diabetes?

Twenty two out of 86 insulin dependent diabetics had serum C4 concentrations below the normal range. None of 41 non-insulin dependent diabetics tested had low concentrations. Low C4 values were seen in insulin dependent diabetes irrespective of the duration of the disease and did not appear to correlate with complement activation. There was a close correlation in C4 values between identical cotwins, even when only one was diabetic. These results suggest that a low serum C4 concentration is an inherited phenomenon and may predispose towards the development of insulin dependent diabetes.

Detection of immune complexes by their complement-dependent binding to bovine conglutinin: technical aspects of a solid-phase immunoenzyme microassay and its application to normal and pathological sera

A micromethod for the solid-phase conglutinin binding assay (Con BA) for the detection of circulating immune complexes (CIC) is described, in which the use of microplates, glucose oxidase-coupled anti-human immunoglobulins and automatic OD recorder contributed to the speed and low cost of this reproducible and sensitive test. The Con BA values of a large population of healthy blood donors had a wide distribution which in our series of 189 appeared to be trimodal. The Con BA values clearly reflected the levels of the main Ig classes (M, G, and A). This was confirmed by follow up of 6 individuals with high initial Con BA values. For 4 of them, a parallel decrease in Con BA value and IgG concentration was observed. In the 2 others, the sustained high level of Con BA remained unexplained. Complement components and activity of these sera were within normal limits. Because of fluctuation in the aggregated human gamma-globulins (AHG) reference curve, expression of results was based upon the standard deviation of 6 normal sera. In view of the above results, these sera were selected from those with the lowest Con BA values. On the basis that Con BA and C1q BA may detect CIC differing in their ag/ab ratio, sera from rheumatoid arthritis and chronic active B hepatitis patients with or without conventional rheumatoid factors (RF) were analyzed by both Con BA and C1q BA. RF-containing sera, likely to contain CIC in antigen excess, contributed exclusively to the highest C1q BA and lowest Con BA values. In contrast C1q BA-Con BA+ sera were preferentially RF negative. It is proposed that the complexes thus detected may be of idiotype-anti-idiotype nature.

Complement studies in splenectomized patients

Total haemolytic complement activity, C2, C5, total alternative pathway activity, factor B, and C3d were measured in 85 splenectomized patients from 1 month to 32 years after splenectomy. Furthermore the patients were investigated for circulating immune complexes. No major deficiencies of the complement factors were detected. In a few patients a reduced C2 level was caused by genetically determined defects or was due to complement consumption in conjunction with circulating immune complexes. The complement levels were normal in 2 patients who had survived overwhelming infections after splenectomy. C5 was elevated in a major proportion of the patients, and it is suggested that this might be caused by post-splenectomy monocytosis. Circulating immune complexes were found in 20% of all cases, irrespective of the presence of residual splenic tissue. Thus the commonly cited impairment of the complement system after splenectomy does not seem to be substantiated, and the deficient resistance against bacterial infections in splenectomized patients does not seem to include abnormalities of the complement system.

Capacity to solubilize immune complexes in sera and synovial fluids from patients with rheumatoid arthritis

Fifty-six sera and 33 synovial fluids from rheumatoid arthritis patients were studied to evaluate their capacity to solubilize immune complexes. A decreased function was found in 65% of rheumatoid synovial fluids when compared with 13 osteoarthritis synovial fluids. The decrease of immune complex solubilization capacity correlated with the decrease of hemolytic activity of the alternative complement pathway (P less than 0.001) and inversely with the level of immune complexes (P less than 0.05). Synovial fluids with low and normal immune complex solubilization capacity were compared; the results confirmed a possible role of the synovial complement system in modulating the size and thus the diffusion and clearance of locally generated immune complexes.

Breakdown product of factor B as an index of complement activation in lepromatous leprosy and its relation with bacillary load

Serum complement profile studied in 50 lepromatous leprosy patients with various bacillary loads demonstrated significantly decreased C3 levels in patients with high bacteriological index (2+ to 4+) as compared with those with lesser bacterial load. In contrast, mean serum levels of C1q and C4 components remained unchanged. The concentration of factor B breakdown product (Ba) and its ratio to factor B increased with the bacterial density and more so in patients with erythema nodosum leprosum. A significant negative correlation was found between serum C3 and Ba levels in most lepromatous patients. Analysis of the data suggested the alternative pathway as the possible mechanism of complement activation in lepromatous leprosy.

Determination of the half-life of C3 in patients and its relation to the presence of C3-breakdown products and/or circulating immune complexes

Measurement of complement components in serum may not accurately assess the degree of activation of the complement system. An alternative approach is the measurement of conversion products of the complement components. The relation between the presence of an increased concentration of C3-conversion products and the metabolism of C3 was investigated. In a group of patients, circulating immune complexes were also measured (Clq-binding test) to see whether the combination of those markers yielded information on the C3 metabolism. In this study it is shown that static measurements of serum C3 levels is of no value for the degree of complement activation. Measurement of C3-conversion products may indicate C3 hypercatabolism (in 8 of the 11 patients with C3-conversion products), but it does not imply depressed C3 synthesis. Detection of circulating immune complexes by the C1q-binding assay did not always indicate a C3 hypercatabolism. Of 12 SLE patients studied, in 9 of them, a C3 hypercatabolism was detected, and 5 of these patients were clinically characterized by the presence of minor disease symptoms. Overall, the results indicated that detection of circulating immune complexes and/or C3-conversion products could not be used as an absolute measure for insight into the C3 metabolism.

Influence of time, temperature and coagulation on the measurement of C3, C3 split products and C4

Quantitative and qualitative immunoelectrophoretic analyses of circulating C3, C3 split products and C4 were performed in matched EDTA plasma and serum obtained from 5 normal subjects and stored for up to 48 h at room temperature (18 degrees C-22 degrees C) and 4 degrees C. Fluctuations in apparent levels of C3 were greater in serum than plasma stored at room temperature, a fall in levels seen by 24 h being followed by a significant increase. By contrast, levels of C3 did not alter if stored at 4 degrees C. C4 levels in both EDTA plasma and serum remained unchanged for 24 h, a slight decrease being seen at 48 h. Levels of C4 remained constant if samples were stored at 4 degrees C. Crossed immunoelectrophoresis revealed a significant progressive decrease in C3 levels and a simultaneous increase in C3c occurring after 4 h in serum and 8 h in EDTA plasma, stored at room temperature. In studies conducted at 4 degrees C, similar but delayed fluctuations were seen. A progressive and significant increase in C3d levels was seen in both plasma and serum samples stored at room temperature, levels rising to 276% (plasma) and 308% (serum) of levels seen at zero time. At 4 degrees C marginal increases in C3d levels only were observed. These results suggest that in vitro degradation of C3 and C4 are readily facilitated by temperature, time and coagulation, and that conditions of collection and storage of samples must be optimized for the accurate definition of activation of the complement cascade.