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PubMed1976

Serum factors activating the alternative complement pathway in autoimmune disease: description of two different factors from patients with systemic lupus erythematosus.

Serum factors which activated the alternative pathway of complement were detected in 10 of 26 patients with systemic lupus erythematosus (SLE), three of 18 patients with mixed connective tissue disease, one patient with scleroderma, and one with Sjögren's syndrome. This activation was detected by conversion of factor B and C3 into split products and by lysis of glutathione-sensitized human erythrocytes under conditions where classical pathway activation was blocked. The serum factors capable of activating the alternative pathway could be seperated into 7S and 19S-type molecules by sucrose density gradient ultracentrifugation. In two patients with SLE, serum factors were isolated by ion-exchange chromatography, preparative electrophoresis, and molecular sieve chromatography. The serum 7S factor was immunochemically identical to the C3 nephritic factor (C3NeF) of hypocomplementemic chronic glomerulonephritis. Antisera to other complement components failed to react with this purified material. The 7S factor was able to activate the alternative pathway in C2 deficient serum, and in normal human serum under conditions where classical pathway was blocked, but was unable to do so in sera depleted of factor B, factor D, and C3. The activity could be removed by antiserum to C3NeF. In contrast, the serum 19S activator of the alternative pathway was not reactive with antiserum to C3NeF. It had a fast gamma mobility on electrophoresis and the activity could be removed by absorption with anti-IgG and anti-IgM. It was suggested that the 19S factors could consist, in part, of immune complexes.

Absorption↗
PubMed1988

Epstein-Barr virus transformed B cell lines derived from patients with systemic lupus erythematosus produce a nephritic factor of the classical complement pathway.

Nephritic factor of the classical complement pathway (C4NeF) is an IgG antibody which stabilizes the C3 convertase (C4b2a) and has been detected in sera from patients with systemic lupus erythematosus (SLE) and acute postinfectious glomerulonephritis. In order to study the production of nephritic factor (NeF), mononuclear cells were isolated from the peripheral blood of patients with SLE and infected with Epstein-Barr virus (EBV) to establish active B lymphocyte cell lines. Supernatants from 15 established B cell lines, as well as from 10 B cell lines established from normal individuals, were investigated for their ability to conserve the classical and the alternative pathway C3 convertases as assessed by EAC3bBb and EAC14b2a stabilizing assays. Supernatants from 2 of 15 B cell lines from patients with SLE, but none from normal individuals, stabilized the classical C3 convertase without having any effect on the alternative pathway C3 convertase. Using anti-human Ig affinity chromatography, we showed that C4NeF activity resided in the IgG fraction; the IgG fraction containing C4NeF activity bound to the C4b2a complex, but not to C4b alone. On gel electrophoresis, following reduction, the heavy chains were slightly heavier than the heavy chains of normal IgG. We were able to isolate C4NeF from the sera of the 2 patients with SLE from whom the positive supernatants were derived, but were unable to detect any C4NeF activity in the sera of the other 13 patients and the 10 normal individuals. Serum and B cell line supernatant-derived C4NeF exhibited comparable characteristics. We conclude that C4NeF produced in vitro by EBV-transformed B cell lines derived from patients with SLE is functionally similar to the conventional C4NeF in serum. These studies confirm the production of autoantibodies by B cells with the ability to stabilize the classical pathway C3 convertase in certain patients with SLE; stabilization of the C4b2a enzyme in these patients is an apparent mechanism for the development of hypocomplementemia. Finally, preparation of homogeneous C4NeF in vitro should improve our understanding of the role of autoantibodies in complement metabolic disturbances in autoimmune diseases.

Autoantibodies↗
PubMed1987

Hypocomplementemic glomerulonephritis in an infant and mother. Evidence for an abnormal form of C3.

A mother developed hematuria during the fourth month of pregnancy, and her nursing infant son from this otherwise uncomplicated pregnancy developed hematuria at 3.5 months of age. Both had a mild glomerulonephritis characterized by mesangial prominence, focal thickening and mottling of the glomerular basement membrane and electron-dense deposits, predominantly in the intramembranous and subendothelial positions. Immunofluorescence studies revealed striking accumulations of C3 and other complement components associated with alternative complement pathway activation within glomeruli, and the presence of small or equivocal amounts of immunoglobulin. C1q, C4 and factor B were not detectable. The glomerular lesion was accompanied by hypocomplementemia. Sera of both mother and infant displayed half normal levels of C3 and factor B, increased levels of C4, and normal levels of 12 other complement proteins. High normal or slight elevation in nephritic factor-like activity was observed in serial serum samples. Studies suggested that this mother and son represent the second kindred having an abnormal form of C3 which produces an alternative complement pathway C3 convertase, C3b, Bb, resistant to control by factor H. No additional affected family members were identified. The course of the nephritis over 7 years without drug therapy has been mild with resolving hematuria and no abnormal proteinuria or decrease in creatinine clearance.

Adult↗
PubMed1981

Hypocomplementaemia due to a genetic deficiency of beta 1H globulin.

An 8-month-old Asian boy who presented with the haemolytic uraemic syndrome was found to have a low haemolytic complement, and in particular a very low C3 level, with a normal C4 level. These abnormalities persisted after recovery and were not associated with the presence of circulating C3 nephritic factor. A clinically healthy 3-year-old brother was found to have an identical complement profile, which indicated increased alternative pathway activation. Both brothers had normal levels of the C3b inactivator, but very low levels of beta 1H globulin (less than 10% of a reference standard serum). The parents, who were first cousins, had half-normal levels of beta 1H globulin, and low levels were found in other members of the family, indicating that the defect was inherited.

Child, Preschool↗
PubMed1977

Acute nephritis in fifty children: clinical and immunological studies.

The main clinical and laboratory findings in a group of 50 children with acute nephritis are described and discussed. All the group had evidence of a streptococcal aetiology. The wide spectrum of presenting complaints, the age distribution and the high incidence among Maori children are noted. The severity of the disease, as indicated by features such as hypertensive crisis, was greater than expected. Fifty per cent of our patients experienced one or more of our defined complications. Encephalopathy was seen in 12% of all patients and severe hypertension in 34%. The striking feature of the laboratory findings was the wide variation in complement changes. No constant patterns emerged which would have implicated either the "classical" or "alternate" pathway for the activation of complement in these patients. An unexpected finding was the relatively high incidence of a transient C3 nephritic factor in post-streptococcal cases. We found also that fibrin degradation products were present in high concentrations in the urine of patients with post-streptococcal nephritis, again an unexpected finding.

Acute Disease↗
PubMedDate not supplied

Complement activation in renal disease.

Perturbation of the serum complement system in glomerulonephritis can be the result of classical pathway activation by immune complexes or of C3 activation by the C3-C5 convertase stabilized by the C3 nephritic factor. Low C3 levels can also be the result of diminished C3 synthesis and possibly, in certain circumstances, of C3 convertases deposited on capillary walls. In glomerulonephritis the complement profile is helpful in diagnosis, in following the course of therapy and in providing insights into pathogenesis. Complement profiles must be interpreted recognizing that a pattern resembling classical pathway activation can be produced by idiopathic nephrotic syndrome, that hypogammaglobulinemia can reduce Clq levels, and that a primary deficiency of factor H or I or both, will secondarily produce subnormal levels of C3 and factor B. With these caveats, the complement profiles typical of systemic lupus erythematosus, membranoproliferative glomerulonephritis, acute glomerulonephritis, acquired Cl inhibitor deficiency, and hypocomplementemic vasculitis syndrome are described.

Antigen-Antibody Complex↗
PubMed1981

A serum C3-activating factor: its characterization and its presence in glomerular deposits.

A non-IgG C3 activating factor (C3AF) isolated from the serum and plasma of a patient with membranoproliferative glomerulonephritis with subendothelial and subepithelial deposits (type III) was studied to define its molecular structure, functional characteristics, and presence in renal biopsies. Alternative complement pathway (ACP) activation of C3 was comparable to that of zymosan, but significantly less than that of IgG C3 nephritic factor (C3NeF). Functionally active isolate contained beta 1H globulin (beta 1H) and the C3AF protein, which had a gamma-electrophoretic migration. beta 1H present in the isolate exhibited an altered gamma-beta electrophoretic mobility. The function of this complex is heat labile. Time/temperature studies demonstrated that inactivated preparations of this isolate show a return to the normal beta migration of beta 1H followed by the development of an alpha 2 electrophoretic migration of the previously gamma-migrating material of functionally active isolate. Normal human serums contain an alpha 2 protein that shows complete antigenic identity with the gamma protein of C3AF, but this alpha 2 protein lacks C3 activating function. On polyacrylamide gel electrophoresis, the C3AF isolate contains a high m.w. protein of 500,000 to 590,000 that is composed of 2 major subunits. Carbohydrate is not demonstrable, and the protein is antigenically distinct from plasma fibronectin. Immunofluorescence studies of renal biopsies of patients with types I and III MPGN revealed the presence of C3AF antigen in granular deposits in 10 of 16 cases. The presence of this antigen in glomerular deposits was associated with C3 and beta 1H, but was independent of Ig. These studies suggest that the mechanism of ACP activation by C3AF results from interference with beta 1H function. The presence of this material in renal biopsies from some MPGN patients further suggests a pathogenetic role in mediating glomerular pathology.

Chemical Precipitation↗
PubMed1983

Mesangiocapillary glomerulonephritis: a long-term study of 40 cases.

Forty cases of mesangiocapillary glomerulonephritis are reviewed for whom both light and electron microscopy and full clinical data were available. Immunofluorescence microscopy (IF) was performed on 23 cases and complement screening (CH50, C4 and C3) on 25 cases, with follow-up period of 5-22 y. The results of EM revealed 17 cases (42 per cent.) of Type I and 23 cases (58 per cent.) of Type II MCGN but only 52 per cent. of Type II cases were correctly identified by light microscopy. Epimembranous deposits were seen as frequently in Type II as in Type I (26 per cent. and 30 per cent.) and fragmentation of glomerular capillary basement membranes (GBM) was seen in 27 per cent. of Type I cases. Overall patient survival was 49 per cent. at 10 y and that of patients who presented with nephrotic syndrome was poor (39 per cent. at 10 y). Persistent hypocomplementaemia with C3 Nephritic Factor was present in 40 per cent.; the survival of these patients was less than those with normal complement levels (70 per cent. vs 100 per cent. at 5 y) and they were also more likely to develop renal failure. Renal failure was more likely to develop in those with a creatinine clearance of less than 100 ml/min at presentation and where the biopsy showed substantial crescents in greater than 20 per cent. of glomeruli. Mean CH50, C3 and C4 was lower in the hypocomplementaemic as compared to normocomplementaemic patients, and there were no differences between Type I and Type II. IF showed immunoglobulins and fibrin as well as C3 in both Type I and Type II cases. Our results support the concept of an immune-complex mediated phase in both types of MCGN, and we further suggest that (a) epimembranous deposits are common in both Type I and Type II and (b) cases with fragmentation of the GBM should be designated Type Ia.

Adolescent↗
PubMed1977

Metabolism of the fifth component of complement, and its relation to metabolism of the third component, in patients with complement activation.

The metabolism of the fifth component of complement (C5), and its relatonship to metabolism of the third component of complement (C3), has been studied in normal subjects and patients by simultaneous administration of radioiodine labeled C5 and C3. In seven normal subjects the fractional catabolic rate of C5 ranged from 1.5 to 2.1% of the plasma pool/h and extravascular/intravascular distribution ratio from 0.22 to 0.78, these values being similar to those obtained for C3, and synthesis rate from 71 to 134 mug/kg per h, In patients with complement activation the increase in fractional catabolic rate of C5 was nearly always less than that of C3. The data also showed that there was increased extravascular distribution of C3 and C5 in most patients and considerable extravascular catabolism of both proteins in some. However, there were differences in metabolic parameters between patients with different types of complement activation. In patients with systemic lupus erythematosus, fractional catabolism and extravascular distribution of C3 and C5 were both increased, and there was marked extravascular catabolism of both proteins. There was increased fractional catabolism and extravascular distribution of C3 in patients with mesangiocapillary nephritis and (or) partial lipodystrophy, and fractional catabolism of C5 was also increased in three of six studies although distribution of C5 was always within the normal range; however, in two patients with nephritic factor in their serum fractional catabolism of C5 was normal despite markedly increased C3 turnover, suggesting that in patients with alternative pathway activation by nephritic factor little or no C5 convertase is generated.

Adolescent↗
PubMed1984

Development and application of an enzyme-linked immunosorbent assay for the quantitation of alternative complement pathway activation in human serum.

We have developed a new, specific, and highly sensitive enzyme-linked immunosorbent assay (ELISA) which quantitates activation of the alternative pathway in human serum, plasma, or on the surface of activators. The ELISA detects the third component of complement (C3b), proteolytic fragment of complement Factor B (Bb), and properdin (P) complex or its derivative product, C3b,P. In the method, activator-plasma mixtures, plasma containing an activated alternative pathway, or other samples are added to the wells of microtitration plates precoated with antibody to P. C3b, Bb,P or C3b,P complexes which become bound are quantitated by subsequently added, enzyme-labeled, anti-C3. The resulting hydrolysis of the chromogenic substrate is expressed as nanograms of C3b by reference to a C3 standard curve. In addition to absolute specificity for activation of the pathway because of the nature of the complex detected by the assay, the ELISA is highly sensitive and able to reproducibly detect 10-20 ng/ml of C3b,P complexes in serum. This value corresponds to 0.0015% of the C3 in serum. In a series of studies to validate the parameters of the ELISA, reactivity was found to be dependent on the presence of alternative pathway proteins, the functional integrity of the pathway, and on the presence of magnesium. Sheep erythrocytes were converted to activators by treatment with neuraminidase. By using a variety of activators, the kinetics of activation and the numbers of bound C3b molecules quantitated by the ELISA were very similar to those measured by C3b deposition. The ELISA also detected identical activation kinetics when MgEGTA-serum and a mixture of the purified alternative pathway proteins were used as sources of the pathway. ELISA reaction kinetics also correlated with the restriction index, a measure of alternative pathway-activating ability. These studies cumulatively validate the ELISA as a direct and quantitative assay for alternative pathway activation. The sensitivity of the ELISA has permitted its use to detect direct alternative pathway activation by several viruses. The ELISA has also shown that certain classical pathway activators trigger the amplification loop of the alternative pathway while others do not. In addition, stable ELISA reactive complexes appeared in the supernatant of mixtures of serum with certain, but not other activators. The ability of the ELISA to detect activation which has already occurred and the stability of the reactive complexes permits studies of clinical sera. Normal human sera (20) contained low levels (5-20 ng/ml) of ELISA-reactive complexes. A proportion of sera from individuals with the adult respiratory distress syndrome (9-10), typhoid fever (8-10), malaria (3-5), gram-negative sepsis (9 of 47), acute trauma and shock (6 f 25), and systemic lupus erythematosus (3 of 29) showed elevated levels of complexes reactive in the alternative pathway ELISA. In contrast, nine sera from patients with circulating C3 nephritic factor were not reactive in the ELISA.

Animals↗
PubMedDate not supplied

Systemic lupus erythematosus, partial lipodystrophy and hypocomplementemia.

A patient with partial lipodystrophy, increased susceptibility to infection and a clinical picture compatible with systemic lupus erythematosus is described. This patient had persistently low serum C3 levels and a C3-cleaving factor similar to the C3 nephritic factor (C3NeF). During periods of disease inactivity, serum levels of the other components of the classical and alternative pathways of complement measured were normal; heat labile opsonic capacity was low, suggesting functional depletion of factors of the alternative pathway of complement activation.

Adult↗
PubMed1976

The cofactors required by C3 nephritic factor to generate a C3 convertase in vitro.

The mechanisms by which a C3 convertase is generated by C3 nephritic factor (NeF) were investigated using purified NeF, C3, C3b, factor B and factor D of the alternative pathway of complement activation. NeF could generate a C3 convertase with C3 and B in the absence of D, and without cleavage of B. At lower concentrations of NeF the addition of D was required to generate a C3 convertase, and B cleavage now occurred. The generation of both the D-independent and D-dependent C3 convertases with NeF was inhibited by preincubation of the C3 source with C3b inactivator (KAF); isolated C3b was more efficient than the C3 preparations used in generating the D-independent C3 convertase with NeF. These experiments indicate that C3b is required for the formation of both convertases, and that the reaction occurring with apparently native C3 is due to trace amounts of C3b. It is concluded that the C3 convertase generated by NeF in the absence of D is C3bB (NeF), and that generated in the presence of D is the feedback convertase C3bBb. The relevance of these experiments to reactions which may occur in vivo is discussed.

Biological Products↗
PubMed1990

Persistent low C3 levels associated with meningococcal meningitis and membranoproliferative glomerulonephritis.

Recurrent meningococcal meningitis is usually related to terminal complement factor deficiencies (C5-C8); however it is not frequent with isolated primary C3 deficiency. Similarly, membranoproliferative glomerulonephritis has been described in association with primary C3 deficiencies and the presence of C3 nephritic factor. We present a case of an 18-year-old woman with relapsing meningococcal meningitis in whom membranoproliferative glomerulonephritis and persistent low serum C3 levels were found. A detailed immunological study was performed, but no other abnormalities in the complement components were found. C3 Nef was also negative. Moreover, the familiar complement studies showed an asymptomatic C4 deficiency in her mother and borderline C3 levels in her sister. The presence of persistent low serum C3 levels in the absence of other immunological abnormalities suggests that this is the cause of the relapsing meningococcal infections and the glomerular disease of this patient. We suggest that a complement deficiency, including isolated C3 deficiency, should be ruled out in all cases of relapsing meningitis. Further, the possibility of glomerular disease should be carefully considered in these patients.

Adolescent↗
PubMed1976

Control of the amplification convertase of complement by the plasma protein beta1H.

An inhibitory activity for an erythrocyte in termediate bearing the properdin (P)-stabilized amplification C3 convertase, PC3bBb, was recognized in whole normal human serum and separated from C3b inactivator by its distinct physicochemical and functional characteristics. The inhibitory activity was found to reside in a protein that was purified to homogeneity and elicited a monospecific antibody in a rabbit. This protein was identified as beta1H and found to have a serum concentration of 516 +/- 89 mug/ml (mean +/- 1 SD). beta1H produced a dose related, first-order loss of convertase function and release of 125I-Bb from the P-stabilized intermediate, indicating a mechanism of action by decay-dissociation of Bb from the complex, PC3bBb. beta1H exhibited only a limited capacity to accelerate decay of C3bBb sites stabilized with C3 nephritic factor or to release 125I-Bb from such sites. Amplification of C3 cleavage by C3bBb may well determine whether initial complement activation by the classical or alternative activating sequence is beneficial or detrimental to the host. Regulation of this amplifying function is now recognized to occur at at least three steps: intrinsic decay which reflects the inherent lability of the C3bBb convertase; extrinsic decay-dissociation of Bb which is mediated by the effect of beta1H; and inactivation of exposed C3b by C3b inactivator. The stabilization of C3bBb by activated properdin minimizes intrinsic decay and protects C3b in the bimolecular complex from C3b inactivator. beta1H restores control of the system by decay-dissociation of the bimolecular complex, therby exposing C3b to C3b inactivator whose irreversible action prevents regeneration of the convertase at that site.

Animals↗
PubMed1976

The complement abnormalities of lipodystrophy.

Investigation of the serum complement system in 25 patients with various forms of lipodystrophy showed no abnormality in three patients with total lipodystrophy; a single patient with limb lipodystrophy had evidence of activation of the classical complement pathway. However, of the 21 patients with partial lipodystrophy, 17 had low serum C3, with normal C4 and C2, concentrations, accompanied in 14 by a serum C3 splitting factor indistinguishable from nephritic factor, suggesting activation of the alternative pathway. These abnormalities occurred in 10 patients without clinically overt renal disease. Seven patients had overt nephritis; renal biopsies obtained in six showed mesangiocapillary (membranoproliferative) nephritis in all. Thus, the majority of patients with partial lipodystrophy have hypocomplementemia. Although nephritis may not invariably develop, the high rate of mesangiocapillary nephritis in these patients suggests that complement activation via the alternative pathway predisposes to the development of this form of glomerular disease.

Adolescent↗
PubMed1980

[Specific measurement of alternate pathway activation of complement in human glomerulonephritides (GN): 125 cases (author's transl)].

C3 cleaving activity through alternate pathway, appreciated by native C3 antigen reduction in the presence of Mg EGTA, has been measured in sera of 40 controls and of 125 GN patients. The normal percentage of native C3 conversion ranged from 0 to 29 in controls (p less than 0.05). The number of positive samples is 0/30 in lupus GN (0%), 13/29 in acute GN (45%) and 26/66 in membranoproliferative GN (39%) with 7/8 in dense deposits subtype. The presence of alternate pathway activators of complement correlated with serum C3 level: their frequency is respectively 0, 0.32, and 0.48 if serum C3 is normal, low, and very low. Such activity correlated also well with alternate pathway C3 activation (low C3 and normal C4): the frequency of positive samples is respectively 0, 0.07, and 0.51 in the presence of No C3 activation, classical pathway activation (low C3 and low C4), and alternate pathway activation. The nature of such serum activators could be nephritic factor, bacterial polysaccharides, polymeric IgA, activated properdin, peculiar immune complexes, or other factors. Such measurement is an improvement immunopathological step in the investigation of human GN.

Complement Activation↗
PubMed1990

Systemic lupus erythematosus in a patient with partial lipodystrophy.

Systemic lupus erythematosus developed in a 35-year-old woman who had partial lipodystrophy since she was 7 years old. To our knowledge, this association has been reported only once. She also had hypocomplementemia, mesangiocapillary glomerulonephritis type II, and a serum assay with positive results for C3 nephritic factor. The association of partial lipodystrophy with other autoimmune disorders suggests an immunologic pathogenesis for this disease.

Adult↗