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

Correlation between immune complexes and prognostic factors in Hodgkin's disease

Serum or plasma samples from sixty-two patients with Hodgkin's disease (HD) were tested by four assays for circulating immune complexes or complement activation products: macromolecular C3 (MMC3), ¹²⁵I-labelled C1q binding (C1qBA), conglutinin binding (KgB) and plasma C3d levels. There was good agreement between the C1qBA, MMC3 and plasma C3d assays, and each gave significantly higher proportions of positive results in patients with symptoms of fever, night sweats and weight loss. The much lower proportion of positive assays by KgB, one out of thirty-three (3%) in asymptomatic and six out of twenty-nine (21%) in symptomatic patients, may reflect an inherent property of complexes or the presence of an inhibitor of conglutination in HD serum.

A positive result in one or more of these assays occurred in twenty-six out of twenty-nine (90%) of symptomatic patients compared with only ten out of thirty-three (30%) in asymptomatic patients. Most of the positive tests in the asymptomatic groups were by the C1qBA, and with one exception, these were from patients with histological types carrying a poor prognosis. In patients with poor prognostic histology, although the MMC3 and C3d assays detecting complement activation correlated with the symptoms, this was not found for immune complexes detected by the C1qBA. The close correlation between positive tests and two features known to adversely affect the prognosis in HD indicates that the detection of immune complexes may be of use in the staging and management of patients with this disease.

A study of the material inhibiting EAC-rosette formation in the sera of patients with nephropathies

Significant levels of EAC-rosette inhibition compared to control subjects were found in the sera of patients with focal and segmental hyalinosis (FSH), membranoproliferative glomerulonephritis (MPGN) and extra-membranous glomerulonephritis (EGN). In patients with IgA disease, although some sera produced high levels of inhibition, the group as a whole did not differ significantly from the controls. Evidence was obtained suggesting that the rosette inhibitory activity was due to immune complexes (IC) bearing C3 rather than C3 fragments. Firstly, the inhibitory activity was precipitable by 4% PEG, a concentration which does not precipitate the C3 fragments. Secondly, the inhibitory activity was selectively removed from the PEG precipitates by an anti-human immunoglobulin G immunoabsorbent. Finally, since it had been suggested that in some instances an unknown serum factor could inhibit EAC-rosette formation and activation of the alternative pathway of complement, the latter was studied and found to be normal in all the sera studied. Taken together, these results suggest that the inhibition of EAC-rosette formation obtained with the sera of the patients studied was due to the presence in these sera of some material behaving as IC. No clear-cut association was, however, seen between rosette inhibition and the presence or absence of Ig or C3 deposits in the kidney.

Detection of circulating immune complexes in patients with glomerulonephritis

A panel of three immune complex (IC) assays was used in this study to test sera from patients with glomerulonephritis (GN): the Raji cell radioimmune assay (IRCA), the radio-labeled C1q binding assay (IC1qBA), and the microcomplement consumption test (MCT). The sensitivity and specificity of each assay was evaluated in preliminary studies, and the greater sensitivity (5 to 10microgram of aggreagated human gamma-globulin (AHG) per ml of serum) and IgG specificity of the IRCA was apparent. Problems related to the preliminary heat inactivation of test sera, the interaction of C1q with substances other than IC, and the effects of suboptimal storage of test sera were experienced with the MCT and, to a lesser extent the IC1qBA. The individual reactivities of the different assays were exploited by using them in combination. Thus ICs were detected by one or more of the assays in 87% of patients with systemic lupus erythematosus (SLE), 65% of patients with GN associated with other systemic diseases, and 39% of patients with primary GN. ICs were detected more frequently in patients with acute GN than chronic GN, and in patients with low serum C3, C4, and properdin factor B (C3PA) levels.

Immune complexes and complement catabolism in ankylosing spondylitis

In serum samples from 37 patients with ankylosing spondylitis (AS), immune complexes were quantitated by the 125I-Clq binding test; in paired plasma samples the C3 breakdown product C3d was measured by an immunochemical method. Compared to results in 30 blood donors, the Clq binding activity was significantly (greater than 2 SD), although discretely, increased in 5 of 8 patients with seropositive AS, but not in other AS patients. All C3d levels were within the normal range. In a parallel investigation, increased Clq binding activity and C3d levels were found in 87% and 90%, respectively, of patients with seropositive rheumatoid arthritis.

Circulating complement breakdown products in patients with rheumatoid arthritis. Correlation between plasma C3d, circulating immune complexes, and clinical activity

Quantitative determination of the small C3 breakdown product, C3d, was used to investigate complement activation in 45 plasma samples from 30 patients with rheumatoid arthritis (RA). The mean plasma C3e level in these samples (3.0 +/- 1.3 mg/100 ml) was significantly increased (P less than 0.001) as compared to patients with degenerative joint disease (0.9 +/- 0.4 mg/100 ml) and healthy blood donors (0.8 +/- 0.5 mg/100 ml). C3d levels were increased by more than s SD in 79% of RA samples. Plasma C3d levels were compared with C3d concentrations in synovial fluid. In most RA patients, the C3d levels were higher in synovial fluid than in plasma. A very significant correlation between plasma C3d levels and circulating immune complexes, as measured by determination of Clq binding activity (Clq BA), was observed (P less than 0.001). C3d levels were more elevated in RA patients with extra-articular disease manifestations (3.8 +/- 1.2 mg/100 ml) as compared to patients with joint disease alone (2.2 +/- 1.0 mg/100 ml). C3d levels and Clq BA were also significantly correlated (P less than 0.001) with the RA disease activity expressed by an index derived from sedimentation rate, joint score, and duration of morning stiffness. A close relationship between C3d levels, Clq BA, and the clinical activity further appeared during follow-up studies. The present observations suggest that a parallel but rather independent activation of the complement system may be induced by immune complexes in circulating blood and in the joint spaces during the course of rheumatoid arthritis.

Correlation between levels of breakdown products of C3, C4, and properdin factor B in synovial fluids from patients with rheumatoid arthritis

Synovial fluids from 31 patients with seropositive rheumatoid arthritis (RA) and 23 patients with seronegative RA had significantly increased levels of breakdown products to C3, C4, and properdin factor B when compared to patients with osteoarthritis (OA) (P less than 0.01). The same patients exhibited a considerable overlap of native C3, C4, and properdin factor B levels when their results were compared with those of OA patients. The parallel increase of C3d, C4d, and Ba levels in patients with RA suggests an activation of the complement system rather than a nonspecific enzymatic breakdown in synovial fluids.

A study of the presence of circulating immune complexes in schistosomiasis

The sera from 51 patients with schistosomiasis were studied for the presence of circulating immune complexes (IC) using two methods, inhibition of EAC rosette formation and precipitation of radio-labelled Clq. The percentage EAC rosette inhibition was significantly greater in the total group of patients compared to the control sera. The material inhibiting EAC rosette formation was precipitable by 4% polyethylene glycol, thus excluding the role of C3 fragments and suggesting that inhibition was due to immune complexes. Using precipitation of radio-labelled Clq significant high values compared to control sera were only obtained in those patients before treatment or with an active infection. The results suggests that material behaving as IC is present in the sera of patients with schistosomiasis and that measurement of the levels of IC may be important in assessing the state of the disease.

Immune complexes and complement hypercatabolism in patients with leprosy

The occurrence of immune complexes in the serum and the level of the C3 breakdown product C3d in the plasma from patients with leprosy were studied by quantitative methods and the results were compared in various forms of the disease. These studies were performed on sixty-two samples from twenty-six patients. The serum 125I-C1q binding activity was found to be increased by more than 2 s.d., as compared to the normal values, in most of the sera from patients with erythema nodosum leprosum (ENL) (80%) and uncomplicated lepromatous leprosy (82%), but also in the sera from patients with tuberculoid leprosy (58%). In vitro studies suggested that immune complexes involving mycobacterial antigens were present in leprosy sera. An increased C3d level (greater than 2s.d.) was also found in most of the plasma from patients with ENL (70%), but rarely in the plasma from patients with uncomplicated lepromatous leprosy (18%) and never in tuberculoid leprosy patients' plasma. The absence of a significant correlation between the 125I-C1q binding activity and the C3d level in leprosy patients may suggest that extravascular immune complexes are involved in the complement activation occurring in ENL. The quantitation of C3d in plasma may be of some practical interest in the early diagnosis of ENL complications of leprosy.

Detection of complement activation by counterimmunoelectrophoresis (CIE)

Counterimmunoelectrophoresis (CIE) was used as a method of detecting activation of the third component of the complement system (C3). Highly purified C3, normal human serum (NHS), EDTA-treated plasma and serum activated with aggregated human immunoglobulin (agg-IgG) or inulin were used as sources of C3 and/or C3 split products. Activation of the alternative pathway of complement was assayed in the presence of EGTA (10 mM) and MgCl2 (0.3 mM), conditions which block activation of the classical pathway. When purified native C3, fresh NHS and fresh EDTA-plasma were tested in CIE against either antisera to whole C3 or to C3 split products, only one precipitin line was found, which was identified as native C3. However, when serum activated with agg-IgG or inulin were tested against the same reagents, two precipitin lines were seen. The first, with more cathodal mobility was identical to that of native C3. The second line had a more anodal mobility, was distinctly separated from the first and contained C3c and C3d as shown immunochemically with specific antisera. Native C3 and split products of C3 were identified by this CIE method in patients showing evidence of activated complement by having subnormal total complement (CH50) levels. When C3 split products were identified, the C3c-C3d precipitin line could always be distinguished from native C3 by its different electrophoretic mobility, even when C3 concentrations in serum varied from 0.25 mg/ml to 1.5 mg/ml. The sensitivity of CIE was compared to that of CH50 by asssaying at different time intervals after agg-IgG was added to fresh NHS. C3c-C3d split products were detected by CIE before any fall in CH50 and at all times when a significant decrease in CH50 was present. This study shows that the CIE technique is a highly sensitive, specific and rapid method for detecting activation of the complement system via classical or alternative pathways in human disease.

Activation of the alternative complement pathway in systemic lupus erythematosus

Serum factors activating the alternative pathway of complement in vitro, independent of classical pathway activation was demonstrated in six of eleven patients with systemic lupus erythematosus (SLE). These serum factors were detected by lysis of gluthathione-sensitized human erythrocytes and by C3 and factor B conversion in the presence of EGTA (10 mM) and MgCl2 (0-3 mM), conditions which blocked activation of the classical pathway but permitted activation of the alternative pathway. In order to determine if in vivo activation of the alternative pathway of complement was present in SLE, highly-purified factor B was labelled with radioactive iodine (125I), and its metabolism studied in the eleven patients with SLE and in twelve control subjects. All six patients with serum factors capable of activating the alternative pathway in vitro, had in vivo evidence of alternative pathway activation as measured by increased fractional catabolic rate (FCR) of factor B. Two patients without demonstrable alternative pathway activating factors in their sera had an elevated FCR of factor B. Six of the patients with increased FCR of factor B had disease limited to skin or joint and one had lupus nephritis which was inactive at the time of study. One of the four patients who were in clinical remission had elevated FCR. This study demonstrates that a significant number of patients with SLE of relatively mild disease activity had evidence of alternative complement pathway activation. This activation did not appear to be limited to patients with lupus nephritis and raises the possibility that it could also be related to some of the extra-renal manifestations of SLE.

C3b inactivator in the rheumatic diseases. Measurement by radial immunodiffusion and by inhibition of formation of properdin pathway C3 convertase

C3b inactivator (C3bINA) has been measured in biologic fluids by radial immunodiffusion using a monospecific antiserum prepared in rabbits, and by a hemolytic assay which measures the reduction in the capacity of EAC43 cells bearing limited C3b sites to form C3B, the alternative pathway C3 convertase. The radial immunodiffusion and hemolytic assays show a good correlation (r = 0.86 P less than 0.001). Measurement of C3bINA concentrations in the sera of patients with systemic lupus erythematosus showed that during exacerbations of disease activity C3bINA concentrations tended to be lower, usually in association with reductions in C4, C3, factor B, and properdin, and sometimes with reductions of the alternative pathway proteins, factor B, and properdin alone. Supranormal values for C3bINA were found in the sera of 14 of 20 patients with seropositive rheumatoid arthritis and 3 of 9 seronegative patients, but none of 7 patients with degenerative joint disease. Synovial fluid concentrations of C3bINA, after correction for total synovial fluid protein and serum concentration of the enzyme, were significantly reduced in patients with rheumatoid arthritis compared to patients with degenerative joint disease (P less than 0.05). In both serum and synovial fluid from patients with rheumatoid arthritis, there was a good correlation between the concentrations of C3bINA and those of C3, factor B, and properdin, but not that of C4, suggesting that levels of C3bINA may serve to modulate recruitment of the properdin amplification loop in this disease.

Circulating and intra-articular immune complexes in patients with rheumatoid arthritis. Correlation of 125I-Clq binding activity with clinical and biological features of the disease

The correlation between the incidence and level of immune complexes in serum and synovial fluid and the various clinical and biological manifestations of rheumatoid arthritis has been studied. Immune complexes were quantitated using a sensitive radioimmunoassay, the 125I-Clq binding test, in unheated native sera and synovial fluids from 50 patients with seropositive (RA +) and 45 with seronegative (RA -) rheumatoid arthritis, 17 with other inflammatory arthritis, and 37 with degenerative and post-traumatic joint disease. The following observations were made: (a) when compared to the results from patients with degenerative and post-traumatic joint diseases, the 125I-Clq binding activity (Clq-BA) in synovial fluid was found to be increased (by more than 2 SD) in most of the patients with RA + (80%) and RA - (71%) and in 29% of patients with other inflammatory arthritis; the serum Clq-BA was also frequently increased in both RA + (76%) and RA - (49%) patients, but only exceptionally in patients with other inflammatory arthritis (6%); (b) a significant negative correlation existed between the Clq-BA and the immunochemical C4 level in synovial fluids from patients with RA + and RA -; (c) neither the serum nor the synovial fluid Clq-BA in rheumatoid arthritis significantly correlated with the erythrocyte sedimentation rate, the clinical stage of the disease, or the IgM rheumatoid factor titer; and (d) the serum Clq-BA in patients with rheumatoid arthritis and extra-articular disease manifestations (40 +/- 34% in those with RA +,32 +/- 29% in those with RA -) was significantly increased as compared to the serum Clq-BA in patients with joint disease alone (24 +/- 30% in those with RA +, 10 +/- 13% in those with RA -). Experimental studies were carried out in order to characterize the Clq binding material in rheumatoid arthritis. This material had properties similar to immune complexes: it sedimented in a high molecular weight range on sucrose density gradients (10-30S) and lost the ability to bind Clq after reduction and alkylation, or after acid dissociation at pH 3.8, or after passage through an anti-IgG immunoabsorbant. DNase did not affect the Clq BA. These results support the hypothesis that circulating as well as intra-articular immune complexes may play an important role in some pathogenetic aspects of rheumatoid arthritis. The 125I-Clq binding test may also be of some practical clinical value in detecting patients who have a higher risk of developing vasculitis.

Binding of components of the properdin system to cultured human lymphoblastoid cells and B lymphocytes

Immunofluorescence studies showed that properdin (P) and factor B bind to C3-C3b receptor bearing human lymphoblastoid cells (Raji, Daudi) and B type human peripheral lymphocytes (HPL). P bound to Raji cells first incubated with normal human serum (NHS). EDTA, but not EGTA, halted the binding of P to cells incubated with NHS. However, fixation of P to Raji cells, after incubation with NHS first reacted with inulin, was independent of Ca++ and -g++ ions. Fixation of P to Raji cells depended on the presence of C3 or C3b and occurred in the absence of factor D and factor B. Binding of P to B type HPL was detectable only after incubation of these cells with NHS first reacted with inulin; under these conditions binding of P to Raji cells was also greatly enhanced. With both Raji cells and HPL, factor B was detectable on cell surfaces only after incubation of these cells with NHS first reacted with activators of the P system. Binding of factor B to cells required the presence of C3b and binding or stabilization of cell bound factor B necessitated the presence of activated P. P and factor B were detectable only on cultured cells having C3-C3b receptors. However, incubation of NHS with all lymphoblastoid cell lines studied resulted in activation of P and cleavage of factor B. Binding of P and factor B to cells may follow one of three sequences; (a) activated P in fluid phase combines with C3, factor D, and factor B, and the whole complex fixes to cellular C3-C3b receptors via its C3 moiety; (b) C3b generated in fluid phase combines with P, C3, factor D, and factor B and binds to C3-C3b receptors; or (c) C3 or C3b first binds onto the C3-C3b receptors and thereafter interacts with P, factor D, And factor B. Binding of components of the P system to cells or other particles may relate to such biological phenomena as lysis, phagocytosis, proliferation, attraction of other cell types, and alteration of responsiveness to external stimuli.