Detection of complement activation by counterimmunoelectrophoresis (CIE)

Dr Eng M. Tan: a tribute to an enduring legacy in autoimmunity

At the age of ninety years, Dr Eng Meng Tan has had a remarkable impact on the accumulated knowledge of autoimmune diseases, including seminal findings in systemic lupus erythematosus (SLE) and a wide range of other autoimmune diseases. Dating to the first description of the Sm (Smith) autoantibody in SLE, his focus has been the use of autoantibodies as probes to identify and elucidate novel cellular molecules and then translating these discoveries into biomarkers and immunoassays for a wide range of these diseases and, later, cancer. He led efforts to standardize autoantibody nomenclature and testing protocols. Through his mentorship a great number of trainees and collaborators have had remarkably successful careers, and by that virtue he has garnered a remarkable continuing legacy.

Antibody response to meningococcal polysaccharides A and C in patients with complement defects

Patients with defects of terminal complement components are particularly exposed to the risk of developing neisserial infections and seem to respond poorly to meningococcal capsular polysaccharide (PS) C via natural immunization. The sole meningococcal PSC is, on the other hand, an excellent immunogen in normal people. Considering the great importance of vaccine prophylaxis for the prevention of meningococcal infections in patients with complement defects, it is crucial to study the antibody response to the sole meningococcal PS in these patients. We therefore analysed the levels of anti-PSA and PSC antibodies in the members of four families including patients with homozygous and heterozygous defects of C7, C8 or factor H, before and after vaccination with the sole PSA + C. Surprisingly, we found the highest levels of antibodies before vaccination in homozygous subjects, followed by heterozygous and normal controls, whereas, after vaccination, homozygous subjects showed the lowest increase of specific antibodies, indicating their relative incapability to respond to sole meningococcal PS. In conclusion, this study demonstrates (1) the capacity to respond to meningococcal PS via natural immunization by patients with total complement defects, and (2) the low responsiveness to meningococcal PS via vaccine immunization by the same patients. We propose that vaccination should be given to patients lacking specific antibodies and their serological response should be assessed. In addition this study confirms previous observations on a likely lower immunogenic power of meningococcal serogroup C via natural immunization compared with the better immunogenicity of the sole PSC.

Complement activation and sensitizing antibodies in Lyme borreliosis. A microbial adherence immobilization assay for Borrelia burgdorferi (MAIA-BB)

A report is presented about the capability of complement to directly clump Borrelia burgdorferi. The new phenomenon which has been termed "microbial adherence", is either antibody-independent or requires the presence of "sensitizing" antibodies depending the strains tested. Microbial adherence is associated with immobilization and killing of borrelias. A microbial adherence immobilization assay for B. burgdorferi (MAIA-BB) was developed to detect sensitizing antibodies in patients with Lyme borreliosis and in B. burgdorferi-infected animals.

Functionally active complement is present in human ovarian follicular fluid and can be activated by seminal plasma

Human ovarian preovulatory follicular fluids (FF) from 10 women were analysed for their complement contents. Functionally active complement was detected in all the fluids studied in amounts similar to those present in normal human serum. Pooled FF was challenged by seminal plasma in order to determine whether seminal plasma could activate FF complement, the pattern of such an activation and the possible consequences on the reproductive function. FF complement activation occurred during the incubation with seminal plasma with features including alternative pathway activation, factor B and C3 conversion and reduction in total haemolytic complement, as well as an inhibition by seminal plasma of the FF complement response to a new activating challenge. Possible consequences for fertilization, implantation of a fertilized ovum and local defence mechanisms against viruses and bacteria are discussed.

Complement, complement activation and anaphylatoxins in human ovarian follicular fluid

Functionally active complement was sought and detected in human follicular fluids obtained during the pre-ovulatory period. All the functional complement activities tested, including total haemolytic complement, classical pathway activity and alternative pathway activity were present in nine fluids from four different donors with values within the normal serum range. The immunochemical analysis demonstrated the presence of complement factors from C1 to C9, of B and of C1 INH, H, I. Complement anaphylatoxins were found employing RIA techniques in amounts significantly higher than in human plasma, thus demonstrating that follicular fluid complement, at least during the pre-ovulatory period, is partially activated. A possible role for urokinase-like substances in such an activation was indicated by further in vitro experiments. The presence of active complement in follicular fluid can be relevant for the function of the enzymatic multi-factorial mechanism of ovulation.

Complement components in neonatal sepsis

Complement components C3, C1q, factor B and breakdown products of C3, i.e. C3c and C3d, were evaluated in the diagnosis and prognosis of sepsis in 24 neonates with proven sepsis. The complement components were measured by electroimmunodiffusion and breakdown products by counterimmunoelectrophoresis (CIEP). The babies with sepsis were found to have decreased levels of C1q and factor B as compared with suitably matched healthy controls. No statistically significant depression was observed in C3 levels of infected babies. However, breakdown products of C3, i.e. C3c and C3d, were detected in 58.3% of these babies. The breakdown products of C3 were not present in any of the healthy controls. The degree of depression of complement components was of no prognostic significance in neonatal sepsis.

Complement activation is associated with the presence of specific human immunodeficiency virus (HIV)-anti-HIV immune complexes in patients with acquired immunodeficiency syndrome-related complex or lymphoadenopathy syndrome

The complement system was examined in a group of eight patients (six with lymphoadenopathy syndrome (LAS); two with acquired immunodeficiency syndrome (AIDS)-related complex (ARC], who were found to be human immunodeficiency virus (HIV)-positive, for the presence of specific HIV-anti-HIV complexes. A significant impairment of the classical and/or alternative pathway was found associated with the presence of cleavage fragments of C3 and/or B and a significant reduction in the complement factors studied. Ultracentrifugation fractions of serum samples obtained from one of the patients were assessed for the detection of specific HIV-anti-HIV (GP41-anti-GP41) complexes and were incubated with normal human serum to determine their complement activation capacity. A clear complement activation was found with the fraction in which a clear peak of HIV-anti-HIV (GP41-anti-GP41) immune complexes was present. The results demonstrate that specific immune complexes and complement activation are sometimes concomitantly present in patients with AIDS-related disease and that specific immune complexes may be one of the causal factors of the pathogenesis of complement activation in these patients. Possible consequences for the severe immune regulation with relevance to the dramatic failure in treating the virus effectively are discussed.

Clinical application of new technique that measures C4d for assessment of activation of classical complement pathway

A new laser nephelometric technique that measures C4d for the assessment of the activation of the classical complement pathway was developed. C4d was isolated from other larger C4 related molecules at a final concentration of polyethylene glycol of 12% and then quantitated by laser nephelometry using a commercially available antiserum, which reacts with C4d determinants. C4d standard (100%) was produced by exhaustive activation of the classical pathway in pooled normal human serum using heat aggregated human immunoglobulin. Serial dilutions of the standard provided a reference curve against which clinical samples were read. Patients with rheumatoid arthritis showed significantly higher C4d values (mean 53.8%) than controls (21.7%; p less than 0.001). The technique proved accurate, rapid, and suitable for the routine laboratory evaluation of complement activation through the classical pathway, and it may be useful in the management of those conditions in which complement activation has a pathogenic role.

Activation of complement and coagulation in juvenile dermatomyositis

In patients with juvenile dermatomyositis (JDM), small vessel occlusion and thrombosis result in a decrease in the capillary: muscle fiber ratio. We studied 15 patients with JDM. Six of 7 patients with clinically active JDM had elevated levels of C3d. Moreover, concentrations of fibrinopeptide A and factor VIII-related antigen were significantly increased in patients with clinically active JDM.

Complement in the pathophysiology and diagnosis of human diseases

Complement is a humoral effector system composed of 21 plasma proteins that was identified initially because of its cytolytic effects. In addition to cytolysis, complement has a number of different functions related to inflammatory and other host defense processes. The description of the reaction mechanism includes: (1) activation of the classical pathway through recognition of IgG and IgM antibodies by C1q, (2) activation of the alternative pathway which is usually achieved without participation of immunoglobulins, (3) generation of proteolytic enzymes composed of heteropolymers that cleave certain precursor proteins, (4) formation of the membrane attack complex (MAC), and (5) participation of control mechanisms. Methodologies for studying protein concentration and functional activities of complement components include not only the classical hemolytic techniques but also the extremely sensitive new radioimmunoassays and enzyme immunoassays for measuring the products of complement activation that are generated in vivo. Examples of genetically controlled complement deficiencies have been published for most complement components. The symptomatology of some of these patients serves to emphasize the protective role of complement. Acquired deficiencies are significant not only as laboratory aids in diagnosis and to evaluate the course of certain diseases, but also to indicate possible pathogenic disease mechanisms. Recently, it has been recognized that the complement proteins with genes located in the HLA region are polymorphic. Certain variants of proteins C2, C4, and factor B occur with higher frequencies in certain diseases than in the general population, which appears to be of great practical importance in laboratory medicine.

Anti-F(ab')2 antibodies that interfere with interpretation of the anti-C3 assay for immune complexes in children with rheumatic diseases

Results of the solid phase F(ab')2 anti-C3 radioimmunoassay for immune complexes were abnormal in sera from some patients with juvenile arthritis and in many patients with other forms of chronic inflammation. However, C3 failed to block positive reactions of sera from patients even though it did block the reaction when aggregated IgG was added to normal sera. Moreover, positive sera reacted with nonspecific F(ab')2 fragments from several species. High correlation coefficients were obtained between abnormal results in the anti-C3 assay with juvenile arthritis sera and reactions with goat, mouse, and rabbit F(ab')2, but less so with human F(ab')2. Sera from patients with systemic lupus erythematosus or cystic fibrosis had similar reactions but different species specificities. After sucrose density fractionation, the reactivity with nonspecific anti-F(ab')2 was only in the IgG-containing fractions, but anti-C3 activity was in both IgG-containing fractions and the fractions between IgG and IgM. We concluded that anti-F(ab')2 antibodies are common in children with inflammation and may interfere with interpretation of assays using F(ab')2 anti-C3 for detection of complexes.

Activation of human complement by crude and purified antigens from Echinococcus granulosus

Hydatid cyst fluid of Echinococcus granulosus was found to interact with human complement. This interaction resulted in the depletion of hemolytic complement in normal serum and in the electrophoretic conversion of C3 and factor B. The results provided evidence of an activation of complement via the alternative pathway when hydatid cyst fluid was used in the mixtures. Also purified hydatid antigen preparations were found to interact with complement in vitro; this interaction resulted in the consumption of complement not only via the alternative pathway, but also via the classical pathway.

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.

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.

Double-decker rocket immunoelectrophoresis for direct quantitation of complement C3 split products with C3d specificities in plasma

A double-decker rocket immunoelectrophoresis (DD-RIE) method for direct quantitation of complement split products with C3d determinants in human plasma is described. The usefulness of the DD-RIE method for monitoring C3 activation has been assessed and compared with conventional crossed immunoelectrophoresis (CIE) for C3c determination in a patient with iatrogenic septic shock and patients with rheumatoid arthritis. In contrast with CIE the DD-RIE method is quantitative by reference to a standard curve based on an internal reference C3d preparation and its sensitivity and assay capacity are superior to CIE. All reagents and antibody preparation are commercially available and the production of standards is easy. No overlapping was observed between C3d values in plasma from healthy persons and patients with active classical rheumatoid arthritis. The DD-RIE is highly suitable for routine use in laboratories of clinical immunology.

Component concentrations and activation of the complement system in neonatal illness: a preliminary study of necrotizing enterocolitis

Determinations of C3, C4, and C5 concentrations by radial immunodiffusion, and assays for the activation products of C3, C3c and C3d by counterimmunoelectrophoresis, were performed on 80 infants. Seven nonbacteremic preterm infants with necrotizing enterocolitis (NEC) or probable NEC (PNEC) were found at the time of diagnosis to have a significantly lower mean concentration of C3 (P less than 0.05, 1-tailed) without C3 activation when compared to other noninfected preterm infants. Ten full-term and 63 preterm infants were studied prospectively during the first days of life, and were then followed for the postnatal development of localized or systemic infection. Assays for the detection of C3 activation products were negative in all these infants. Four preterm infants who developed PNEC after 5 or more days without clinical illness had low original concentrations of complement components. The pathogenesis of NEC may not involve primarily complement activation, and susceptibility to this condition may be related to pre-existing deficiencies in complement component concentrations relative to gestational age, or to defective activation of C3 in the presence of certain bacterial species and strains.

Clinical applications of immunofixation: detection and quantitation of complement activation

The methods currently in use for the detection and quantitation of complement activation products are slow and time consuming. We describe a method utilising immunofixation after agarose or cellulose acetate membrane electrophoresis which allows large batches of samples to be screened rapidly for the presence of activation products of C3 and factor B. Further, after immunofixation on agarose the conversion product may be quantitated by densitometry. This method gives similar results to those obtained by crossed immunoelectrophoresis. Using both this technique and crossed immunoelectrophoresis we have been able to confirm that C4 activation occurs during electrophoresis in the absence of EDTA and that in the presence of EDTA it is not demonstrable even in patients with active immune complex disease.

Immunochemical quantitation of complement components of Clq and C3 in sera and synovial fluids of patients with bone and joint diseases

The amount of the initiating complement component (Clq) in the classical pathway and the first essential component (C3) in the alternative complement pathway were measured with a single radial immunodiffusion (SRID). A high ionic strength was used corresponding to that of 0 . 25 M NaCl and 0 . 01 M EDTA to avoid nonspecific binding of Clq with immune aggregates. Measurements were made on sera and/or synovial fluids from 165 patients with various bone and joint diseases. Values of Clq and C3 in synovial fluids were also expressed as ratios to that of albumin in the same specimens to avoid the influence of differences in volume of synovial fluid in various diseases, and this appeared to provide a reliable index reflecting pathological conditions. Both serum Clq and C3 levels were raised highly in rheumatoid arthritis, gout, and osteomyelitis, but the extent of the elevation of C3 was less conspicuous. Values of Clq and C3 in synovial fluids also markedly increased in rheumatoid arthritis.

Comparison between immunofixation and crossed immunoelectrophoresis for the detection of C3 activation products

C3 breakdown products were measured in 51 fresh and stored sera and/or EDTA plasma samples from 18 healthy subjects, 8 patients affected by essential mixed cryoglobulinaemia, and 15 patients with miscellaneous glomerulonephritis, by simultaneous crossed immunoelectrophoresis and immunofixation. C3 splitting products, as determined by both methods compared well, and showed a highly significant correlation. The advantages and reliability of these two methods are discussed. Immunofixation seems to be the most suitable for routine use in clinical practice, being less expensive and more rapid to perform.

The immunologic and clinical associations of the split products of C3 in plasma in juvenile rheumatoid arthritis

A qualitative counterimmunoelectrophoretic assay for the complement activation products C3c and C3d was used to study plasma from children with juvenile rheumatoid arthritis (JRA) and other rheumatic diseases. Positive tests for C3c,d were found in all patients with active systemic lupus erythematosus (SLE), 7 of 10 patients with active systemic JRA, 16 of 29 with active polyarticular JRA, 7 of 20 with active pauciarticular JRA, and in only 2 of 20 with inactive joint disease. The incidence of positive assays for C3c,d in JRA was increased in the presence of positive latex fixation tests, antinuclear antibody tests, or elevated values for antiglobulins as determined by affinity chromatography, but these associations were not statistically significant. Three joint fluids from children with pauciarticular JRA were negative for C3c,d. These studies show that the subgroups of JRA defined by clinical criteria are heterogeneous by current laboratory parameters and that evidence implicating antigen-antibody complexes in the pathogenesis of JRA is lacking in many patients.

Plasma complement and histamine changes in atopic dermatitis

Fifteen patients with atopic dermatitis were investigated to evaluate the total of complement and histamine. In five patients total serum complement haemolytic activity (CH50) was significantly decreased as was the haemolytic activity of complement components C2 (C2H50) and C3 (C3H50). By counter immunoelectrophoresis split products of C3 were detected. There was no evidence for alternative pathway activation or the presence of an activator of the alternative pathway. In three patients plasma histamine concentrations were elevated. The intensity of the complement and histamine changes observed seemed to be correlated to the severity of the disease.

Immunoelectrophoretic assay for synovial fluid C3 with correction for synovial fluid globulin

Synovial fluid C3 was measured by electroimmunoassay. When C3 was expressed as mg/ml, the amounts found in Reiter's disease, psoriatic arthritis, gout, and systemic lupus erythematosus were significantly different from degenerative arthritis. When C3 was corrected for total protein, the levels for rheumatoid arthritis, Reiter's disease, psoriatic arthritis, and systemic lupus were significantly different from degenerative arthritis. When C3 was corrected for synovial fluid globulin, only rheumatoid arthritis and systemic lupus were significantly different from degenerative arthritis. Correction of C3 for globulin increases the difference between rheumatoid arthritis and degenerative arthritis. A proportion of gouty fluids with a relative decrease in C3 is demonstrated. It is argued that correction of C3 for globulin is more meaningful than correction for total protein. While many nonrheumatoid inflammatory effusions demonstrate split products of C3, the majority of fluids from patients with systemic lupus have none.

Complement and immunoglobulin deposits in the skin of patients with atopic dermatitis

The immunofluorescent patterns of uninvolved and involved skin biopsies from eight patients with atopic dermatitis were studied, using direct immunofluorescence techniques to identify deposits of the immunoglobulins G, A and M as well as the complement factors C1q, C3, C4, C5, factor B and properdin. Immunoglobulin deposits (mainly IgG) were found in five patients, complement deposits in three patients in the basement membrane zone. In three patients the immunofluorescence was positive for C3, in two patients for C1q, C4 and C5. Regarding the factors of the alternative pathway of the complement system, two patients showed deposits of properdin, one of factor B. The changes were not confined to the eczematous lesions, but were found in uninvolved skin too. The most prominent changes were observed in patients with severe disease.