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PubMed1994

The inhibitory effect of factor J on the alternative complement pathway.

Factor J (FJ) is a cationic glycoprotein with inhibitory activity in C1, the first component of the classical complement pathway. This study demonstrates that FJ is able to regulate the activity of the alternative complement pathway. FJ inhibits the generation of fluid-phase and cell-bound alternative pathway C3 convertase, C3b,Bb (C3-cleaving enzyme). Thus, FJ interferes with the generation of alternative pathway C3 convertase when sheep erythrocytes bearing antibody and activated C3 and C4 (EAC4b,3b) are incubated with the individual complement components, factors B, D, and P. FJ accelerates the decay of C3 convertase with a time course similar to that of factor H, and when both regulators are present together, the decay of enzyme activity is faster than when they are added separately. Furthermore, FJ is able to inhibit the cleavage of C3 by factor B in a fluid-phase assay. FJ prevents the initiation of alternative pathway activation in "more stabilized systems" with well known activators of alternative pathway C3 convertase such as C3 nephritic factor (an autoantibody against alternative pathway C3 convertase), cobra venom factor, and rabbit erythrocytes. In these systems, FJ has no effect on C3 convertase stabilized by rabbit erythrocytes or cobra venom factor. In contrast, FJ promotes the dissociation of C3 convertase stabilized by C3 nephritic factor, but with much lower efficiency than in preventing initiation. Direct interaction of FJ with individual components of C3 convertase was shown by a solid-phase binding assay using plates coated with C3, C3b, B, Bb, or FJ. FJ inhibitory activity in the alternative pathway can be modulated by polyanions like heparin. FJ-mediated inhibition in the alternative complement pathway can be modified by surface interactions, as occurs during alternative pathway C3 convertase activation. Thus, when FJ is adsorbed by and eluted from hydroxylapatite and reverse-phase columns, its inhibitory effect on more stabilized systems is lost. This loss of inhibitory activity is fully reversed when FJ is rechromatographed on heparin-Sepharose or Sepharose columns. Taking into account these data, FJ may be included in the group of highly charged molecules that inhibit the activation of classical and alternative complement pathways (i.e. eosinophil major basic protein, protamine, and heparin).

Animals↗
PubMed1992

Activation of the alternative pathway of complement by monoclonal lambda light chains in membranoproliferative glomerulonephritis.

Immunopathological evidence suggests that activation of the alternative pathway of complement (AP) is involved in membranoproliferative glomerulonephritis (MPGN) and in immunoglobulin A nephropathy. In this report we describe an AP dysfunction-associated factor that was isolated from the serum and urine of a patient with hypocomplementemic MPGN. Extensive glomerular deposits of C3, properdin, and of the terminal complement components were observed in the kidney of the patient. In her serum the AP hemolytic activity was virtually absent. When mixed with fresh normal serum, the patient's serum induced a 96% C3 conversion during a 30-min incubation at +37 degrees C. This activity was found to be due to a circulating factor that by immunochemical characterization proved to be a 46-kD monoclonal immunoglobulin lambda light (L) chain dimer (lambda L). Purified lambda L, but not control lambda or kappa L chains from patients with L chain disease, activated the AP in a dose- and ionic strength-dependent manner. Functionally, lambda L was differentiated from C3 nephritic factor (an autoantibody against the AP C3 convertase, C3bBb) by its inability to bind to and stabilize the C3bBb enzyme. Instead, lambda L was observed to interact directly with the AP control factor H. Thus, lambda L represents a novel type of immunoglobulin-related AP-activating factor with the capacity to initiate alternative complement pathway activation in the fluid phase.

Antibodies, Monoclonal↗
PubMed1986

H deficiency in two brothers with atypical dense intramembranous deposit disease.

We report an H deficiency in two Algerian brothers who had early-onset glomerulonephritis. In addition, one suffered from serious lung infections. The H deficiency was defined by undetectable CH50 and AP50, and low levels of H, C3 and B (less than 10% of normal levels). I and classical pathway components, including C4-bp were normal. CR1 was present on both patients' erythrocytes. No nephritic factor or other circulating alternative pathway activator was detected. The parents, who are first cousins, and a healthy brother and sister had half-normal levels of H. These findings favor an autosomal recessive transmission of the H defect. Although by electron microscopy renal biopsies from both patients were typical for dense intramembranous deposit disease, immunofluorescence microscopy showed an atypical pattern with abundant granular C3 deposits within the mesangium and along the capillary walls. Alternative pathway activators, possibly related to dense deposits, may allow the formation of membrane-associated C3/C5 convertases, unusually stable in the absence of H, since C5, C6, C7, C8 and C9 levels were decreased in both patients. This observation may represent an interesting clue to the relationship between nephritic factor, alternative pathway activation, and dense intramembranous deposit disease.

Adolescent↗
PubMed1976

Complement activation in semi-solid medium: Insolubilization of properdin and the third component of complement (C3) in agar gels.

Although the role of properdin in the alternative pathway of complement activation remains unclear, evidence has recently been obtained for the formation of complexes between properdin and other components, including C3. In this study such complexes have apparently been directly visualized. When normal human serum and properdin were allowed to diffuse toward each other in agar gel for 16 hr, a line of precipitation could be seen when stained with Coomassie brilliant blue. The reaction occured at pH 8.6 in 0.05 M Veronal buffer at room temperature but not under physiologic conditions of pH or tonicity. Like the alternative pathway, the reaction was Me++ dependent, occurred with C2- or C5-deficient or hypogammaglobulinemic serum, and did not occur with aged, 52 degrees C-inactivated, C3b inactivator-deficient, or C3-deficient serum. 125I-labeled C3 and properdin but not Factor B were incorporated in the precipitate. Eleven sera containing the C3 nephritic factor failed to produce a precipitate with properdin, but a line of precipitation occurred between seven of these sera and normal serum. This line showed identity with the line occurring between properdin and normal serum. The phenomenon appears to result from formation of insoluble complexes between proteins of the alternative pathway and agar.

Agar↗
PubMed1987

Clinical evaluation and characterization of a unique C3 breakdown factor detected in a patient with acute glomerulonephritis.

A unique factor causing breakdown of the third component of complement (C3) was detected in a patient with acute glomerulonephritis (AGN). The activity was detected by conversion of C3 in a mixture with normal human serum using crossed immunoelectrophoresis. This factor capable of C3 breakdown was not blocked in the presence of ethylenediaminetetraacetic acid (EDTA), heat-pretreatment (56 degrees C, 30 min) und dialysis against 0.1 M phenylmethylsulfonyl fluoride (PMSF). The factor was isolated and characterized by immunochemical and physicochemical techniques. It had beta-mobility on electrophoresis and was separated at a lighter sedimentation coefficient than 7S by sucrose density gradient ultracentrifugation. The activity was absorbed on a DEAE-cellulose column and was eluted under definite conditions of relative salt concentration. These data appear to suggest that this factor is distinct from C3 nephritic factor (C3NeF), immunoglobulins, immune complexes, and other C3 convertases previously described. Moreover, it is clear that the factor was mainly responsible for the C3 activation observed in the patient with acute glomerulonephritis.

Acute Disease↗
PubMed1985

Complement activation by circulating serum factors in human glomerulonephritis.

Factors with the ability to induce a minimum of 20% C3 conversion in normal human serum (NHS) were demonstrated in the sera of nine glomerulonephritis (GN) patients. The nature of these factors was heterogeneous allowing their division into at least three different groups. First, in three cases (membranoproliferative or acute GN) they exhibited the characteristics of C3 nephritic factor, an IgG autoantibody stabilizing the alternative pathway (AP) C3 convertase, C3bBb. Secondly, the serum of one patient (SLE like syndrome, mixed cryoglobulinaemia) with an activator of both pathways and profound hypocomplementaemia showed a temperature-dependent precipitation against autologous and homologous polyclonal IgG. Immunochemical analysis suggested this activity to be due to a monoclonal IgM kappa rheumatoid factor. By gel filtration the C3 converting activity was found in the high molecular weight fractions containing the cryoprecipitable IgM-IgG complexes. Finally, in five cases the exact nature of C-activating factors remained unknown. In four of these the factors were heat labile (30 min at 54 degrees C) C activators in association with post-streptococcal glomerulonephritis. The results suggest that the various C activating factors, possibly distinct from 'classical' immune complexes, are indicators of different types of pathogenetic mechanisms in certain forms of GN.

Adult↗
PubMed1986

Monoclonal anti-human C4b antibodies: stabilization and inhibition of the classical-pathway C3 convertase.

Two IgG mouse monoclonal antibodies (MAbs), Abs 242 and 463, were prepared by fusion of spleen cells from mice immunized with human C4b with a myeloma cell line, P3/ X 63-Ag 8.653. They were assessed for their effect on the activation and stability of the cell-bound classical-pathway C3 convertase, EAC14b2a and on the binding of C2 and C4bp to EC4b. Ab 242 recognized a conformational neoantigen which appeared upon activation of C4 with C-1s and disappeared after chain separation of C4b, while Ab 463 recognized a linear epitope in the beta-chain of C4b. Ab 242 was found to be a C4bp-like MAb: it accelerates the decay-dissociation of C3 convertase and interferes with the binding of C2 to C4b. It also interfered with the binding of C4bp to C4b. These results suggest that Ab 242 recognizes an epitope which is closely related to the C2- and C4bp-binding sites in C4b. Ab 463, on the other hand, was found to be a nephritic factor like MAb: it prolongs the half-life of C3 convertase from 8 to 30 min at 37 degrees C.

Animals↗
PubMed1976

Nephritic factor: Description of a new quantitative assay and findings in glomerulonephritis.

A sensitive quantitative test for nephritic factor (NF) in human serum is reported. The test is based on the capacity of NF to initiate fluid phase consumption of the third complement (C) component in the presence of magnesium ions (Mg++) and of factors of the alternative pathway of C activation. These factors as well as C3 and C5 were supplied by the incorporation of normal human serum (NHS) into the assay mixture. In order to prevent C3 (and C5) consumption via the Ca++- and Mg++-dependent classical pathway, the test was performed in the presence of the chelating agent Mg-ethylene bis (oxyethylene-nitrilo) tetraacetic acid (Mg EGTA) which interacts preferentially with Ca++. The Mg EGTA concentration was found to be critical, a final concentration of 5 mM in the assay mixture being required for optimal results. By its heat stability (54 degrees to 56 degrees C, 30 min), NF could be distinguished from other, heat-labile NF-like factors. The NF test was applied to five categories of patients with glomerulonephritis (GN). Heat-stable NF activity was found in seven of 17 sera in the membranoproliferative glomerulonephritis (MPGN) group. Two of the 12 acute poststreptococcal GN sera had NF-like activity which disappeared upon heating. Serum C3 and proactivator (PA) concentrations varied widely in all groups but a clear positive relationship was found between the presence of NF and low serum C3 concentrations in MPGN. Renal immunofluorescence in MPGN indicated a lesser amount of lg deposited in glomeruli from patients with NF when compared to the NF-negative patients. Both groups had heavy C3 deposits. The availability of a sensitive, quantitative assay for NF may help to provide further insight into the various pathogenic mechanisms in different forms of MPGN.

Acute Disease↗
PubMed1994

Nephritic factors predispose to chronic glomerulonephritis.

Chronic glomerulonephritis has been reported in three rare conditions in which factor H of the complement system does not function normally. Factor H is essential for the inactivation of the C3b-dependent convertase, C3b,Bb, which is constantly being formed in vivo. With factor H dysfunction, this convertase accumulates and produces hypocomplementemia. Twenty-two individuals have been reported with the three forms of H dysfunction, and 12 have displayed evidence of chronic glomerulonephritis. In addition, matings of certain Yorkshire pigs result in offspring that are homozygous deficient in factor H and have a high incidence of a severe hypocomplementemic glomerulonephritis closely resembling membranoproliferative glomerulonephritis type II. The hypothesis proposed is that the nephritis that develops with these forms of H dysfunction is in some way the result of circulating convertase. The corollary is that nephritic factors, also producing H dysfunction and higher than normal circulating levels of the C3b-dependent convertase, are responsible for the glomerulonephritides with which they are associated, mainly membranoproliferative glomerulonephritis types II and III. Nephritic factors are autoantibodies that bind to the C3b-dependent convertase and render it resistant to dissociation by factor H. Although nephritic factors are currently considered epiphenomena, their role in the pathogenesis of membranoproliferative glomerulonephritis should be reconsidered based on the evidence that circulating convertase is nephritogenic.

Autoantibodies↗
PubMed1990

Patterns of complement activation in idiopathic membranoproliferative glomerulonephritis, types I, II, and III.

Complement profiles on 22 hypocomplementemic patients with membranoproliferative glomerulonephritis (MPGN) type I, on 11 with MPGN II, and on 16 with MPGN III, gave evidence that the nephritic factor of the amplification loop (NFa) is responsible for the hypocomplementemia in MPGN II and the nephritic factor of the terminal pathway (NFt) for the hypocomplementemia in MPGN III. In contrast, in MPGN I, there was evidence for three complement-activating modalities, NFa, NFt, and immune complexes. As a result, four different patterns of complement activation were seen. NFa, found in MPGN II, produces a complement profile characterized mainly by C3 depression. In addition, four of seven (57%) severely hypocomplementemic MPGN II patients (C3 less than 30 mg/dL) had slightly depressed levels of factor B, and one of seven (14%) of properdin, but in all the C5 concentration was normal. In contrast, all eight severely hypocomplementemic patients with MPGN II had depressed C5 and properdin levels, and six of eight (75%) depressed levels of C6, C7, and/or C9. Of eight MPGN III patients with moderate hypocomplementemia, 50% had depressed C5 and properdin levels and the remainder, depressed C3 only. This spectrum of profiles is most likely produced by varying concentrations of NFt. In MPGN I, nine of 23 (39%) had a profile indicating only classical pathway activation; seven of 23 (39%), a pattern compatible with NFt alone; four of 23 (9%), evidence for both classical pathway activation and NFt; and three of 23 (13%), a pattern compatible with NFa. The unique multifactorial origin of the hypocomplementemia in MPGN I, often giving evidence of classical pathway activation, together with previously reported differences in glomerular morphology and clinical features at onset, makes it distinct from MPGN III. Depressed C8 levels were found to some extent in all hypocomplementemic states. The levels were uncommonly depressed in patients with NFa, most markedly depressed with NFt, and moderately reduced with classical pathway activation. The cause is not known. Diagnostically, profiles showing classical pathway activation and low levels of C6, C7, and/or C9 are specific for MPGN I. Those showing only classical activation are likewise diagnostic of MPGN I if systemic lupus erythematosus (SLE) and chronic bacteremia are ruled out.

Complement Activation↗
PubMed1984

Physiologic inactivation of fluid phase C3b: isolation and structural analysis of C3c, C3d,g (alpha 2D), and C3g.

The fragments that result from the inactivation of C3b have not been completely characterized. Initial inactivation is catalyzed by the protease factor I, which, in the presence of its cofactor (factor H), cleaves two peptide bonds in the alpha'-chain of C3b. This results in the release of a small peptide (C3f, Mr 3000) from iC3b, which consists of the C3 beta chain covalently bonded to two alpha'-chain-derived peptides (Mr 68,000 and Mr 43,000). Surface-bound iC3b is cleaved at a third site by factor I to produce C3c and C3d,g (or alpha 2D). The factor I cofactor for this cleavage is the C3b receptor that is present on erythrocyte and leukocyte membranes. This report describes the isolation and initial structural characterization of C3c and C3d,g generated in whole blood after complement activation with cobra venom factor. These fragments were compared with the C3 fragments isolated from the serum and plasma of a patient with complement activation in vivo. The fragments were isolated with two solid phase monoclonal antibodies, one of which recognizes a determinant on C3g (clone 9) and one of which recognizes a determinant on C3c (clone 4). C3c isolated from normal blood showed three polypeptides that had apparent m.w. of 75,000, 43,000, and 27,000. The C3d,g consisted of a single polypeptide chain with a m.w. of 40,000. Amino terminal sequence analysis showed that the Mr 27,000 peptide from C3c is derived from the amino terminal portion of the alpha'-chain of C3b, whereas the Mr 43,000 peptide is derived from the carboxy terminus of the same chain. Amino terminal sequence analysis showed also that C3g is derived from the amino terminus of C3d,g. The C3 fragments isolated from a patient with partial lipodystrophy, nephritic factor activity, low serum C3 levels, and circulating C3 cleavage products showed a more complicated pattern on SDS-PAGE. The fragment isolated with clone 9 had an apparent m.w. of 40,000, identical to C3d,g generated in vitro, and it had the same amino terminal sequence as C3d,g generated in vitro. The eluate from insolubilized clone 4, however, showed prominent bands with Mr of 75,000, 56,000, 43,000, and 27,000, together with a triple-banded pattern at 68,000 and a minor band at 80,000. This eluate thus appears to contain C3c, and iC3b or an iC3b-like product. The origin of the Mr 56,000 and Mr 80,000 peptides have not yet been determined. These studies, with previous data, definitively order the C3c and C3d,g peptides in the alpha-chain of C3.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1976

Alternative pathway of complement: demonstration and characterization of initiating factor and its properdin-independent function.

A novel component of the properdin system has been discribed which represents a heretofore unrecognized human serum protein. The protein has been tentatively termed the initiating factor (IF) because it functions in the initial reaction of the properdin pathway. IF is a 170,000 dalton beta-pseudoglobulin which is composed of two presumably identical 85,000 dalton chains linked by disulfide bonds. The protein reacts with antibody to nephritic factor, which is defined by its activity and is found in the serum of patients with certain nephritides. The activity of IF is heat stable. Upon treatment of serum with activators of the alternative pathway, the initial C3 convertase is assembled from IF, Factors D and C, C3, and magnesium without participation of properdin. It is the function of the enzyme to deposit C3b on the surface of the activator particles, thereby affording generation of the solid phase enzymes of the pathway, a process that is a prerequisite for properdin activation. By exposure to low pH, IF assumed the electrophoretic mobility of psi-globulin and acquired the ability to generate without activators a fluid phase C3 convertase in serum. Serum depleted of IF did not allow activation of the properdin pathway. Serum depleted of properdin did permit activation of the pathway and expression of cytolytic activity. These results raise the possibility that IF represents the recognition unit of the pathway.

Animals↗
PubMed1985

Hageman factor in experimental nephrotoxic nephritis in the rabbit.

This study was performed to investigate whether the Hageman factor (HF) system might contribute to glomerular damage in vivo. HF was purified from rabbit plasma. The proteolytic activation pattern of 80,000-dalton rabbit HF was the same as that previously reported for human HF. Anti-HF IgG, raised in a goat, was monospecific as judged by immunodiffusion analysis and inhibited HF activity in rabbit plasma. A telescoped model of nephrotoxic nephritis in the rabbit was developed using guinea pig antirabbit glomerular basement membrane IgG injected into rabbits preimmunized against guinea pig IgG. In this model protein excretion was increased by days 3 to 4 in association with glomerular influx of acute inflammatory cells. By days 5 and 6 fibrin was present within glomerular capillaries, beneath endothelial cells, in Bowman's space, and in proximal tubules. By fluorescent microscopic analysis rabbit IgG and C3 had accumulated along the glomerular capillary wall; however, no HF was detectable in glomerular capillary wall over the initial 10 days of glomerular injury. Positive fluorescence for HF was seen within Bowman's space and in tubules along with albumin and plasmin- and fibrin-related antigens. Although the circulating antigenic HF concentration did not change during the glomerular injury, the rate of turnover of 125I-HF did increase. However, when this was factored for turnover of 131I-albumin in a paired study, the relative turnover of 131I-albumin was found to be faster than that of 125I-HF. Proteolysis of 125I-HF in plasma consistent with HF activation was noted in only one of these rabbits in spite of a decrease in antigenic C3 level to 54% of baseline. The 125I-HF appearing in urine of nephritic rabbits had undergone proteolysis from the native 80,000-dalton parent molecule to form fragments of 50,000 and 30,000 daltons, compatible with HF activation. Urine from nephritic rabbits also contained procoagulant activity that was HF dependent. These results are compatible with the concept that HF passively crosses the damaged glomerular filter where it may become activated in Bowman's space or in fluid draining damaged glomeruli in this model of nephrotoxic nephritis in the rabbit.

Animals↗
PubMedDate not supplied

An IgG autoantibody which inactivates C1-inhibitor.

Antibodies are considered to play a specific pathogenic role in certain disease states such as myasthenia gravis, Graves' disease and autoimmune haemolytic anaemia. Autoantibodies which interfere with the function of enzyme cascade systems have also been described in diseases such as acquired haemophilia (anti-factor VIII antibodies) and glomerulonephritis (C3 nephritic factor). The identification of these autoantibodies is crucial to an understanding of the aetiology of such diseases and is also of importance in revealing the inter-relationships of the immune system with other biological pathways. This is the first report of an immunoglobulin G (IgG) autoantibody reactive with C1-inhibitor (C1-Inh), a pivotal inhibitor of the inflammatory response which is known to inactivate proteins of the complement, kinin, fibrinolytic and 'contact phase' systems. This autoantibody was isolated from a patient with a novel variant of acquired angioedema and C1-Inh dysfunction. This finding highlights the involvement of the immune system in the pathogenesis of disorders characterized by the presence of dysfunctional inflammatory response proteins.

Autoantibodies↗
PubMed1977

[Hyperacute rejection of an HL-A identical renal allograft (author's transl)].

Hyperacute renal allograft rejection is described in a patient suffering from mesangio-proliferative glomerulonephritis. The transplanted kidney was HL-A identical and the direct cytotoxic cross-match between the recipient's serum and donor lymphocytes was negative. Intrarenal consumption of C 3, but not of C 1 q, C 4, total haemolytic complement, IgG or Igm was demonstrated. Immunofluorescence studies exhibited dense granular deposits of C 3, but not of IgG, IgM C 1q or C 4. These findings together with the observation of beta 1 C-beta 1A converting activity in the patient's serum, raised the possibility that the alternative pathway of complement activation induced by nephritic factor could have operated in this case. Further studies will be necessary to clarify the question whether hyperacute rejection of renal allografts is only antibody mediated or not.

Acute Disease↗
PubMed1980

The interaction of C5 with C3b in free solution: a sufficient condition for cleavage by a fluid phase C3/C5 convertase.

We have measured the interactions of C3b with C5 in free solution under conditions that favor detecting weak binding interactions (high C3b and low C5 concentrations and low ionic strength). When a mixture of 125I-C5 (2 X 10(-8) M) and unlabeled C3b (3.8 x 10(-5) M) was ultracentrifuged in a sucrose gradient, virtually all of the C5 sedimented to the position of a 13 to 14S complex. In contrast, a sedimentation rate for C5 of 9S was obtained in the absence of C3b. The ability to bind C5 was observed to be a property of C3b since native C3 was unable to bind C5. It was also found that beta 1H by itself could inhibit the binding of C5 to cell-bound C3b. From inhibition studies, we estimate that the association constant for the C3b-C5 interaction is on the order of 2 x 10(6) M-1 in a low ionic strength buffer (mu = 0.06) and 5-fold weaker at physiologic ionic strength. C5 bound to C3b in free solution was cleaved by nephritic factor-stabilized fluid phase C3bB. C5 activation did not occur on omitting C3b. We conclude that the ability to bind C5 is a property of C3b molecules whether surface bound or in free solution and that when C5 is bound in either fashion, it can be cleaved by a fluid phase C3/C5 convertase.

Animals↗
PubMedDate not supplied

[The activation of the complement system in various connective tissue diseases].

A knowledge of the complement system in patients with collagen diseases is of interest as it may serve to indicate the existence of activity or non-activity in these diseases. We have studied the existence or non-existence of the activity of the complement system through evaluation of the levels of C3, as well as the implicated mechanism of the classical or alternate pathways through the measure of C'4 and C'3 proactivator components. Quantitation of complement components was obtained by electroimmunodiffusion, employing specific antiserum. From the results obtained, we observed that the complement activity in patients with SLE, the classic pathway was affected more (7 patients of the 24 studied), than the alternate pathway (3 patients). However, in those patients affected by sclerodermia, there seems to be an equal incidence of the activation of complement through both pathways (2 patients with activation through each way). Also of interest is the existence of a patient with SLE and another affected by sclerodermia in which a selective reduction of C'3 was observed. This observation suggests the possible existence of a selective destruction, perhaps mediated through a factor type such as the nephritic factor. However, there may exist other patients of whom we have already commented on, with a parallel reduction in the three components which suggests a change in the synthesis or in the simultaneous activation in both of the pathways. When realizing the comparative studies of the state in which the immunoglobulins (IgG, IgA and IgM) and complement components are to be found, the conclusion is that there is no significative correlation between the two. This is particularly interesting as it assumes the necessity of knowing the state of the complement and not only of the immunoglobulin, in order to know the state of activity in which the process is.

Complement C3↗