Additional studies on human C5: development of a modified purification method and characterization of the purified product by polyacrylamide gel electrophoresis

Purification of human complement protein C5

Complement C5 is cleaved by proteolysis in the terminal phase of complement activation generating the pro-inflammatory C5a and membrane attack complex nucleator C5b. Whereas purification of its paralogues C3 and C4 from plasma is relatively straightforward, C5 purification is more complicated due to the lower amounts present and overlaps with the much more abundant C3 during several chromatographic steps. Here we describe our procedure for purifying homogenous, monodisperse, and crystallizable C5.

Binding of C3 fragments on top of adsorbed plasma proteins during complement activation on a model biomaterial surface

In the present study we investigate whether complement activation in blood in contact with a model biomaterial surface (polystyrene) occurs directly on the material surface or on top of an adsorbed plasma protein layer. Quartz crystal microbalance-dissipation analysis (QCM-D) complemented with enzyme immunoassays and Western blotting were used. QCM-D showed that the surface was immediately covered with a plasma protein film of approximately 8 nm. Complement activation that started concomitantly with the adsorption of the protein film was triggered by a self-limiting classical pathway activation. After adsorption of the protein film, alternative pathway activation provided the bulk of the C3b deposition that added 25% more mass to the surface. The build up of alternative pathway convertase complexes using purified C3 and factors B and D on different protein films as monitored by QCM-D showed that only adsorbed albumin, IgG, but not fibrinogen, allowed C3b binding, convertase assembly and amplification. Western blotting of eluted proteins from the material surface demonstrated that the C3 fragments were covalently bound to other proteins. This is consistent with a model in which the activation is triggered by initiating convertases formed by means of the initially adsorbed proteins and the main C3b binding is mediated by the alternative pathway on top of the adsorbed protein film.

Opsonization of yeast cells with equine iC3b, C3b, and IgG

The main opsonins in serum are antibodies and complement factor C3. The opsonization mechanisms including complement activation and deposition are important in studies of phagocytosis and of mechanisms of microbial immune evasion. The objective of the present study was to monitor the deposition of complement C3 and IgG from equine serum on yeast cells (Saccharomyces cerevisiae) using a flow cytometric immunoassay. Correlations were made between the opsonic coating and phagocytic capacity using equine blood neutrophils. In addition, the bound C3 fragments were characterized by SDS-PAGE and Western blot analyses. Opsonic coating of yeast with equine C3 and IgG occurred rapidly with detectable levels with as little as 0.75% serum. C3 deposition was a result of complement activation and no passive adsorption was observed. When complement was inactivated, the fluorescence indicating IgG deposition increased 3-6-fold, indicating spatial competition between C3 and IgG at binding. Opsonization with 1.5% serum led to suboptimal equine neutrophil phagocytosis of yeast cells which was dependent on complement activation by the classical pathway. With > or =6.25% serum, IgG contributed to opsonization and phagocytosis. With 50% serum and more, C3 was deposited also by the alternative pathway. Phagocytosis rates became optimal with 3% serum, and did not increase further with higher serum concentrations. The main form of C3 on the yeast cells was iC3b and the rest was C3b without any detectable breakdown products (C3c or C3dg). The equine complement components are similar in size to the human equivalents. It may be concluded that opsonization of yeast particles leading to phagocytosis, occurs at very low serum concentrations (1.5%) and that it is dependent on activation of the classical complement pathway at this low opsonic level. This is an important finding for efficient host defense, e.g. extravascular phagocytosis at infection sites.

Phosphorylation of complement component C3 after synthesis in U937 cells by a putative protein kinase, casein kinase 2, which is regulated by CD11b: evidence that membrane-bound proteases preferentially cleave phosphorylated C3

It was our aim in this study to investigate the possibility that the third component of complement (C3) is phosphorylated during synthesis and secretion in U937 cells. Labelling of U937 cells with [32P]Pi, followed by immunoprecipitation of C3 from cell lysates and culture supernatants at different time points, showed that C3 was phosphorylated intracellularly immediately before release into the medium, which initiated cleavage of the protein into an iC3b-like fragment. Stimulation of CD11b/CD18 increased phosphorylation 7-fold, from a basal level of 2%. The phosphorylation sites in C3 did not resemble those described previously for casein kinase (CK) 1, cAMP-dependent protein kinase A or calcium- and phospholipid-dependent protein kinase C. Instead, protein kinase CK2 was suggested inasmuch as: (1) CK2 was detected both on the cell surface and on shed microparticles; (2) phosphorylation of purified C3 by microparticles was abolished by a monoclonal antibody, anti-CK2; (3) the [32P]Pi tag of both phosphorylated C3 (secreted from U937 cells) and of microparticle-phosphorylated C3, which was cleaved either by membrane proteases or by leucocyte elastase, was found in a 40 and a 70 kDa polypeptide; (4) both secreted C3 and C3 phosphorylated in vitro were much more susceptible to cleavage by proteases. Generation of C3 fragments provides a means by which U937 cells can stimulate nearby cells which are expressing complement receptors. The present study demonstrates that the cleavage of C3 is controlled by an intracellular phosphorylation event regulated by CD11b/CD18.

Purification and characterization of porcine C3. Studies of the biologically active protein and its split products

Separation techniques for obtaining pure and biologically active swine C3 have been improved in this study. Using these procedures and through the further characterization of porcine C3, the possibilities for developing more specific techniques for the analysis of the complement system in swine have been improved. Plasma was initially treated with protease inhibitors, polyethylene glycol (PEG)-fractionation, plasminogen-depletion and a rapid chromatographic desalting step. The essential fractionation was carried out by DEAE-Sephacel chromatography. Contaminants were removed by size-exclusion (Sepharose CL-6B)- and hydroxylapatite-chromatography. The final recovery reached 56% with 73% retaining specific hemolytic activity. The amino acid composition (98.33%), the functional compatibility and the secondary structure of fragments and intact protein indicate a high degree of homology with human C3. In contrast with the findings of earlier studies was the considerable immunologic cross-reactivity observed with human C3, and the size difference between the human and the swine C3-beta subunit, which was found to be 10 kDa lighter than the human analogue. The finding that the swine C3b/iC3b/C3c fragments do not separate from C3 by agarose electrophoresis, unlike the human analogues, demonstrated that this commonly used simple parameter for the detection of complement activation cannot be used in the porcine model.

Purification and characterization of IgG immunoconglutinins from patients with systemic lupus erythematosus: implications for a regulatory function

The levels of IgG immunoconglutinins in plasma from patients with rheumatoid arthritis, systemic lupus erythematosus and primary biliary cirrhosis were monitored by ELISA. High levels of IgG immunoconglutinins were found mainly in plasma from patients with systemic lupus erythematosus. These immunoconglutinins bound to microtitre plate-fixed C3, C3b and C3c but poorly to C3d. This binding was inhibited by particle-bound C3b and iC3b but not by the corresponding soluble fragments. Furthermore, Western blot analysis revealed no immunoconglutinin-binding to reduced C3 peptides and no binding was shown to soluble C3 alpha and beta chain by ELISA. IgG immunoconglutinins were purified from three plasma specimens by affinity chromatography on activated thiol sepharose ATS/C3 fragments. Two immunoconglutinin preparations that preferentially recognize ATS-C3b, inhibited C5-convertase function by 50-100% while one immunoconglutinin that recognized ATS-C3d,g had no effect. The two former immunoconglutinins also inhibited all three factor I cleavages in C3 alpha chain but the latter inhibited only the third cleavage. None of the immunoconglutinins affected the binding of complement-coated anti-BSA/BSA complexes to CR1 (CD35) on human erythrocytes, but the two immunoconglutinins that inhibited all factor I cleavages also inhibited the factor I-induced release of anti-BSA/BSA complexes from CR1. The results show that immunoconglutinins recognize specific epitopes on bound C3 fragments and that they are able to modulate C3-mediated functions.

Synthesis of complement component C5 by human B and T lymphoblastoid cell lines

Human B and T lymphoblastoid cell lines were shown to synthesize C5. C5 synthesis was quantitated with an enzyme-linked immunosorbent assay (ELISA) that utilized a pool of C5-specific monoclonal antibodies (mAbs). Some level of C5 synthesis was detected in all eight of the B and T cell lines examined. In three of the cell lines, C5 was detected in both culture supernatants and whole cell detergent lysates, whereas in the other five cell lines, C5 was detected only in the cell lysates. Lymphoblastoid cells with both distributions of C5 were shown to synthesize a messenger RNA that was similar in size to the C5 mRNA expressed by the HepG2 hepatoma cell line. Estimates of the concentration of the C5 transcript in poly(A)+ RNA from lymphoblastoid and HepG2 cells suggested that C5 mRNA levels in the lymphoblastoid cell lines were comparable and about one-tenth of the levels in HepG2 cells. Lymphoblastoid C5, isolated by immunoaffinity chromatography from the supernatants of 35S-labeled cultures, had the same subunit composition as plasma-derived C5, but had an alpha subunit of slightly smaller relative mass.

Distinctive expression of neoantigenic C3(D) epitopes on bound C3 following activation and binding to different target surfaces in normal and pathological human sera

Binding of C3 to sheep erythrocytes in a serum-free milieu (EAC14oxy2, EAC142) has previously been shown to mimic the antigenic change that occurs upon denaturation of C3 in sodium dodecyl sulphate (SDS), whereby neoantigenic C3(D) epitopes are exposed. The present paper deals with C3 bound to various target surfaces which are known to modulate the functional properties of C3 in different ways. Bound C3 fragments on serum-treated human aggregated gammaglobulin, zymosan, rabbit and sheep erythrocytes, and on circulating immune complexes isolated from sera of patients with rheumatoid arthritis and systemic lupus erythematosus, were shown to be mainly in the iC3b form. By RIAs, employing polyclonal antibodies, the range of C3(D) antigenic epitopes of 125I-labelled SDS denatured C3 expressed by the particle-bound iC3b was monitored. The physiologically bound iC3b on all tested particles expressed wide range of C3(D) epitopes and each type of particle-bound C3 exposed its individual range. By competition ELISA specific C3(D) alpha epitopes were monitored, employing monoclonal antibodies. A distinct difference in the expression of these epitopes was observed in iC3b bound to various test particles in the presence of normal serum and in iC3b present on circulating immune complexes from pathological sera. Considering that the neoantigenic C3(D) epitopes have been shown to be associated with different functions of C3, the distinctive antigenic expression of each type of serum-treated particle might reflect different functional forms of the protein.

A simplified assay for the detection of C3a in human plasma employing a monoclonal antibody raised against denatured C3

A monoclonal antibody raised against SDS-denatured C3 was shown to react with both solid-phase C3a and unfragmented C3. However, in the fluid phase the antibody was found to bind only to C3a and not to native C3. These findings indicated that the antibody could be used in an assay to detect C3a in human EDTA-plasma without prior separation of C3a from native C3. A simple and rapid competition ELISA was developed which monitored soluble C3a. 200 microliter of C3a (8 ng) was absorbed to plastic wells over night at 4 degrees C. Thereafter, 50 microliter of sample and 50 microliter of constant amounts of monoclonal antibody conjugated with beta-galactosidase, were incubated for 60 min at 37 degrees C. After washing, the colour reaction was started by adding nitrophenyl-galactopyridine to the wells. The microtitre plate was incubated at 37 degrees C for 30 min and the staining intensity was quantified at 405 nm. The assay detected both C3a and C3ades arg. A strong correlation was obtained between the new technique and an RIA which used an acid precipitation step for the separation of C3a prior to the determination of C3a (r = 0.9). Significantly higher levels of C3a were detected both in plasma from patients with immune complexes (93 +/- 9 ng/ml; P less than 0.1) and in plasma from patients treated in blood oxygenators (140 +/- 19 ng/ml; P less than 0.05) than in plasma from normal subjects (74 +/- 4 ng/ml). The results were not affected by repeated freezing and thawing of the plasma samples.

Enhanced reactive lysis of paroxysmal nocturnal hemoglobinuria erythrocytes. Studies on C9 binding and incorporation into high molecular weight complexes

As part of a broader analysis of the mechanism(s) by which the most sensitive (type III) paroxysmal nocturnal hemoglobinuria (PNH) erythrocytes are excessively sensitive to reactive lysis by isolated C5b6, C7, C8, and C9, we have compared type III PNH (PNH-III) and normal human E in respect to both total specific binding of 125I-C9 and the proportion of cell-bound C9 appearing in high molecular weight (HMW) complexes. In a previous report, we found that after exposure to purified C5b6 and 125I-C7, specific C7 binding and, by implication, EC5b-7 formation were equal for PNH-III E and normal E. In the present study, C8-dependent binding of 125I-C9 to PNH-III EC5b-7 and normal EC5b-7 was also similar, although lysis of the PNH-III E was up to five times greater; that is, PNH-III E required fewer bound C9 molecules to produce an effective lytic site than did normal E. To quantify radioactivity in monomeric and HMW forms of membrane-bound C9, lysed and unlysed E were subjected to low ionic strength buffers to convert all E to ghosts. These ghosts were solubilized in 0.1 or 2% SDS (without reduction) and electrophoresed on 2.4-11% polyacrylamide gradient gels followed by autoradiography and densitometric scanning. With 0.1% SDS, broad, heterodisperse zones of HMW C9 were recovered from both PNH and normal ghosts; the amounts of C9 incorporated into the HMW complexes were similar for PNH-III E and normal E. In selected experiments, 125I-C7 could be shown in these same HMW bands. When membranes were solubilized in 2% SDS, the overall proportion of HMW C9 complexes compared with dimer and monomer C9 was reduced on both PNH and normal membranes. In many, but not all experiments, more of the highest mol wt C9 complexes were detected from PNH-III E membranes solubilized in 2% SDS than from normal or PNH-II E membranes similarly treated. When antibody-sensitized E were lysed by purified C1-C9, PNH-III EA bound far more C9 than did normal EA, and both lysis and C9 incorporation into HMW complexes were markedly and proportionately increased over normal; however, lytic efficiency of 125I-C9 bound to PNH EA was equal to or less than that bound to normal EA.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation of human complement component C3 from small volumes of plasma

A method for the isolation of 8-10 mg of human C3 from 20 ml of plasma is described. The procedure is simple and rapid with excellent yields in hemolytic activity (74%) and antigenic activity (68.7%). It consists of polyethylene glycol precipitation, DEAE-Sephacel chromatography, and immunoadsorption. The final product is free of contaminating proteins as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The simplicity and speed of this procedure allow for the continual availability of hemolytically active C3.

An assessment of the extent of antigenic analogy between physiologically bound C3 and C3 denatured by sodium dodecyl sulphate

Three previously defined antigenic subsets of C3 (C3(S), C3(D) alpha and C3(D)beta) clearly distinguish native C3 from C3 that has been denatured in the presence of sodium dodecyl sulphate (C3-SDS): C3-SDS expresses antigens of all 3 subsets, while native C3 only expressed C3(S) antigens. The radioimmunometric assessment performed in this study revealed that 90% of the C3(S) and C3(D)alpha and 70% of the C3(D)beta antigens demonstrable in C3-SDS also was expressed by physiologically bound C3b on sheep erythrocytes. The antigenic properties of bound C3b were not shared by soluble C3b, which (like soluble C3) only expressed C3(S) antigens, nor did soluble C3b 'spontaneously' released from complement-treated target cells express antigens other than C3(S). We therefore conclude that the expression of C3(D) antigens, under physiological conditions of activation, reflects a conformational modification unique for bound C3b and occurring to an extent comparable to that of C3 in the presence of a strong denaturant. Additional studies further revealed that the antigenic profile of bound C3b is determined by a heterogeneous population of molecules differing in their relative expression of the C3(S), C3(D)alpha and C3(D)beta subsets.

Artificial metastases and decrease of fibrinolysis in the nude mouse lung after hemithoracic irradiation

X-irradiation to the nude mouse lung and the ensuing pulmonary metastasis of the injected human cancer cells were investigated. Human cancer cells were injected intravenously into nude mice following 20 Gy right hemithoracic irradiation. The right lungs showed evidence of metastasis while metastasis was slight in the non-irradiated left lung. Platelet aggregation and fibrin deposition occurred around the arrested cancer cells in the capillaries of the right lung. The fibrinolytic activity of the irradiated right lung was lower than that of the non-irradiated contralateral lung. Natural killer cell activity was lower in the right-lung-irradiated mice than in the non-irradiated mice. We conclude that when the target organ is exposed to X-irradiation, there will be a decrease in fibrinolytic activity, a condition paving the way toward a metastasis.

Isolation of human complement factors C3, C5 and H

An improved method for simultaneous purification of complement factors C3, C5 and H from human plasma has been developed. Using an initial batch separation technique with QAE-Sephadex, followed by chromatography on SP-Sephadex and gel filtration in Sephadex G-200, 600 mg of highly pure C3 can be prepared from 1600 ml of plasma. Simultaneously about 70 mg of highly pure factor H and 30 mg of C5 are obtained by chromatography of post SP-Sephadex material on DEAE-Sephacel. A small amount of C3 in the C5 pool is removed by anti-C3-Sepharose. By maleylation or citraconylation of reduced and alkylated C3, the constitutive polypeptide chains are modified in a way that made them separable by ion exchange chromatography.

High-density lipoprotein and its apolipoproteins inhibit cytolytic activity of complement. Studies on the nature of inhibitory moiety

Human high-density lipoprotein (HDL) and its apolipoproteins A-I and A-II inhibit complement-mediated lysis of human and sheep erythrocytes. This inhibitory activity under study is exerted after C9 is bound to membrane-associated C5b-8 complexes but prior to completed assembly and insertion of the C5b-9 complex. In this paper, we define some structure-activity relationships of the inhibitory moiety. With the exception of weak lytic inhibitory activity found in LDL/VLDL pools and in some unconcentrated minor fractions of plasma obtained by hydrophobic chromatography, all inhibitor activity was found in fractions which contained either apolipoprotein A-I, apolipoprotein A-II, or both. Intact HDL has a high level of inhibitor activity but delipidation by chloroform-methanol extraction was associated with an increase in activity on a protein-weight basis. Purified apolipoprotein A-I and apolipoprotein A-II exhibited equal inhibitory activity, greater than that exhibited by intact HDL. Nevertheless, ultracentrifugal fractions in which no free apolipoproteins could be demonstrated still possessed inhibitory activity. These experiments suggest that delipidation of HDL is not necessary for expression of inhibitor activity, although we could not rule out the possibility that apolipoproteins in dynamic equilibrium with HDL are responsible for the inhibitor activity observed in whole serum and plasma and in HDL preparations. Limited proteinase digestion completely abolished the inhibitory activity of partially delipidated HDL. Phospholipase C had little or no effect on the inhibitory activity of delipidated HDL, apolipoprotein A-I or apolipoprotein A-II, but reduced the inhibitory activity of intact HDL. These data suggest that the phospholipid polar headgroups are not necessary for inhibitory activity. However, the loss of these headgroups is associated with decreased activity, possibly due to increased hydrophobicity of HDL, or increased association among HDL micelles, and subsequent decrease in effective molar concentration of the inhibitory moiety.

Simplified assays of hemolytic activity of the classical and alternative complement pathways

Simplified hemolytic assays for the classical (CP) and alternative (AP) pathways of complement (C) were developed. The CP function was tested with sensitized sheep erythrocytes in a diluent containing Ca2+ and Mg2+, while AP was tested with unsensitized rabbit erythrocytes in a diluent containing Mg2+-EGTA. In contrast to the commonly used hemolytic titration (CH50) assays, the present techniques tested the activity in reaction mixtures containing C at final dilutions which would not affect its function. These ranges fell between 1/1 and approximately 1/20 for CP and between 1/1 and approximately 1/3 for AP. With the adopted assay techniques single aliquots of serum were tested at single final dilutions of 1/8 for CP and 1/2 for AP, in the presence of excess target cells. Hemolysis was allowed to take place at 37 degrees C for 20 min. The number of cells lysed by CP and AP under these conditions was directly proportional to the dose of serum and unaffected by the presence of a large excess of target cells. Each pathway was tested independently of the other. Serum C levels, measured as described, correlated strongly with those determined by standard hemolytic titration (CH50) assays. The modified assays should offer less laborious alternatives for the functional assay of C than current routine procedures.

Human platelet activation by C3a and C3a des-arg

C3a liberated from C3 by treatment with C3 convertase (or by trypsin) induced aggregation of gel-filtered human platelets and stimulated serotonin release. At concentrations of 10(-10) M to 8 X 10(-12) M, C3a induced aggregation when added alone to platelets. However, at lower concentrations (2 X 10(-12) M) C3a did not aggregate platelets directly but exhibited highly significant synergism (two-way analysis of variance P less than 0.0001) with ADP in mediating platelet aggregation and release of serotonin. Removal of the C-terminus arginine from C3a abolished anaphylotoxin activity but did not affect the platelet-stimulating activity of the peptide. C3a and C3a des-arg were equally reactive in mediating platelet aggregation and release of serotonin. Further C3a and C3a des-arg exhibited synergism with ADP of equal significance in both aggregation and the release reaction. The concentrations of C3a required for the platelet-stimulating activity involve relatively small number of molecules per platelet (4,000-10,000 for the synergistic reaction with ADP). These data suggest the possibility of a C3a (C3a des-arg) receptor on human platelets. This premise is strengthened by the demonstration ultrastructurally of C3a on the platelet membrane subsequent to C3a stimulation.

Expression of C5a-like biological activities by the fifth component of human complement (C5) upon limited digestion with noncomplement enzymes without release of polypeptide fragments

Experimental conditions required for the expression of maximum C5 activation upon limited trypsin hydrolysis were determined to be 0.008 mol of trypsin/mol C5 in a reaction mixture containing 1 mg C5/ml veronal-buffered saline incubated at 37 degrees C for 30 min. Employing these optimal incubation conditions, the primary or preferred site of trypsin hydrolysis of the C5 alpha-chain resulted in the production of C5 alpha 1 (molecular weight, 90,000) and C5 alpha 5 (molecular weight, 25,000) fragments that remained disulfide bonded to the modified C5 molecule (C5'try). Detailed structural-functional analyses clearly indicated the trypsin-mediated conversion of the C5 alpha-chain to C5 alpha 1 and C5 alpha 5 was responsible for the acquisition of neutrophil lysosomal enzyme-releasing and chemotactic activities. Gel filtration column chromatography under physiological ionic strength, pH 7.4, or in the presence of 0.2% SDS further demonstrated that at least 90% of the total recoverable C5a-like biological activity was mediated by the 210,000 molecular weight forms of trypsin-modified C5. Other physiologically relevant, noncomplement protease enzymes (alpha-thrombin, plasmin, and elastase) also activated C5 to express C5a-like reactivities. Analysis of alpha-thrombin-induced, C5 alpha-chain cleavage events by SDS-polyacrylamide slab gel electrophoresis indicated that the mechanism of alpha-thrombin-activation of C5 is similar to that described for trypsin. Reconciliation of this novel mechanism of C5 activation by trypsin with previously published results, and a discussion of the biological significance of noncomplement enzyme-mediated activation of C5 as it might relate to inflammatory processes in vivo, was presented.

The fifth component of complement (C5): purification without activation

In the course of our studies on the structural change of C5 by acidification (U. Rother et al., 1978), we found that the C5 preparations purified according to published methods contained more or less activated C56. When added to sensitive target cells (guinea pig or chicken erythrocytes), C5 mediated lysis by C7-C9 without the addition of C6 or any activation procedure. Generation of C56 was probably due to drastic changes in the physicochemical environment during purification. Such changes like high or low pH or high ionic strength were shown to cause activation. A method for purification of C5 is described in which polyethyleneglycol (PEG) or (NH4)2SO4 precipitation, as well as low or high pH, was avoided. As a last step, traces of C6 were removed by affinity chromatography. The resulting preparation was free of C56. Activation by acidification was not possible without the addition of C6. The total recovery of C5 was 12% with almost no loss of specific activity.

Inhibition of the lytic action of cell-bound terminal complement components by human high density lipoproteins and apoproteins

Human serum lipoproteins are known to participate in or modify several immunologically relevant responses, including the inhibition of target cell lysis initiated by fluid-phase C5b-7 (reactive lysis). We now report that human high density lipoproteins (HDL) can inhibit the complement (C) lytic mechanism after C5b-7, C5b-8, and even C5b-9 have been bound to the target membrane. This inhibitory activity of serum or plasma copurifies in hydrophobic chromatography with antigenically detected apolipoprotein A-I (apoA-I), the major HDL apoprotein, and with HDL in CsCl density gradient ultracentrifugation. Although HDL is more active than its apoproteins in fluid-phase inhibition of C5b-7-initiated reactive lysis, the HDL apoproteins are more effective after C5b-7, C5b-8, or C5b-9 have become bound to human or sheep erythrocytes (E). Highly purified HDL apoproteins, apoA-I and apoA-II, both have greater inhibitory activity than whole HDL on a protein weight basis, and some evidence has been obtained that apoA-I dissociating spontaneously from HDL may be the principal inhibitory moiety in physiological situations. HDL lipids themselves are inactive. The HDL-related inhibitors are ineffective when incubated with EC5b-7 and removed before C8 and C9 are added, and only minimally effective on cell-bound C5b-8 sites before C9 is added. They exert their most prominent inhibitory activity after C9 has been bound to EC5b-8 at low temperature, but before the final temperature-dependent, Zn(++)-inhibitable membrane damage steps have occurred. Therefore, HDL or its apoproteins do not act to repair already established transmembrane channels, but might interfere either with insertion of C9 into the lipid bilayer or with polymerization of C9 at C5b-8 sites. This heat-stable inhibitory activity can be demonstrated to modify lysis of erythrocytes in whole serum, i.e., it does not depend upon artificial interruption of the complement membrane attack sequence at any of the above-mentioned stages. Contributions of the target membrane itself to the mechanism of inhibition are suggested by the observations that, in contrast to sheep or normal human E, lysis of guinea pig E or human E from patients with paroxysmal nocturnal hemoglobinuria is inhibited poorly. This is the first description of a naturally occurring plasma inhibitor acting on the terminal, membrane-associated events in complement lysis. Although further study is required to assess the physiologic or immunopathologic significance of this new function of HDL, the HDL apoproteins or their relevant fragments should be useful experimentally as molecular probes of the lytic mechanism.

Purification and characterization of human kidney plasminogen activator dissimilar to urokinase

The tissue activator was extracted with 2 M ammonium thiocyanate and purified by L-arginine methyl ester, concanavalin A and ion-exchange chromatographies, and Sephacryl S-200 gel filtration in buffers containing Triton X-100 and/or ammonium thiocyanate. The final preparations had specific activities of 25 000-40 000 IU/mg protein and were shown to be a single band with an apparent molecular weight of 54 00 by SDS-polyacrylamide gel electrophoresis with or without reducing agent. When subjected to isoelectric focusing, its major component had an isoelectric point of approx. 8.2 with minor components. (7.8-8.6). The purified tissue activator was a serine protease, dissimilar to urokinase in some respects including antigenicity, strong affinity to insoluble fibrin monomer and hydrolytic activities for synthetic substrates. The crude extract contained another plasminogen activator with antigen identity to urokinase, which constituted approx. 15% of the total activity in crude extract. These findings indicated that human kidney would produce at least two plasminogen activators, namely, the tissue activator as a major plasminogen activator and urokinase.

Effects of fibrin and fibrinogen-degradation products on the growth of rabbit aortic smooth muscle cells in culture

Fibrin contains a factor which promotes growth of the mesenchymal cells and such may be related tissue repair. Effects of fibrin and fibrinogen degradation products (FDP) on the growth of smooth muscle cells (SMC) of rabbit aortas in culture were investigated, in relation to atherogenesis. Fibrin, free from plasminogen enhanced the proliferation of SMC during the experimental period of 48 h. Fibrin, rich in plasminogen also stimulated the proliferation of SMC within 24 h, but inhibited it after 48 h. FDP (fragments D and E) inhibited the proliferation of SMC. SMC of rabbit aortas demonstrated plasminogen activator activity. Thrombin and urokinase exhibited no promoting effects on the growth of SMC. These results support the hypothesis that the proliferation of SMC is stimulated by fibrin and later inhibited by FDP, as produced by the fibrinolytic activity of SMC. It is proposed that the metabolism of fibrin in the arterial wall may be of importance in the regulation of SMC proliferation and that the coagulation-fibrinolysis system may play a significant role in atherogenesis.

Responses of normal and malignant cells to collagen, collagen-derived peptides and the C5-related tumor cell chemotactic peptide

Two variant subpopulations of murine fibrosarcoma cells that differ significantly in their malignant potential and normal mouse fibroblasts were compared with regard to ability to respond chemotactically to collagen, collagen-derived peptides and the C5-derived tumor cell chemotactic peptide. Two distinct patterns of responsiveness were observed. The normal fibroblasts and non-metastasizing fibrosarcoma cells responded to the collagen products but not the C5 peptide. The metastasizing fibrosarcoma cells responded to the C5 peptide but not to the collagen products. These findings emphasize the similarities between the normal fibroblasts and the non-metastasizing fibrosarcoma cells.

Human complement in the arachidonic acid transformation pathway in platelets

Arachidonate-mediated release of 14C serotonin and thromboxane B2 (TXB2) is significantly enhanced in the presence of complement. Only purified complement components C5, C6, C7, C8, and C9 are required for this reactivity. No known activating mechanism of the classical or alternative pathway is required, nor is C3. In the absence of exogenously added complement, platelet membrane-bound complement components play an essential role in modulating arachidonate-mediated serotonin release. Incubation of platelet membranes with arachidonate and C5--C9 led to the production of dimers of the membrane attack complex (C5b--9) on the platelet surface. These macromolecular complexes were eluted from the platelet membrane and were identified physicochemically and morphologically. The possibility arises that C3 in association with C5--C9 is required for mobilization of the arachidonic acid from the phospholipid of the platelet membrane. Once the arachidonic acid is mobilized, C3 is no longer required, C5--C9 being sufficient to modulate this pathway leading to enhanced production of TXB2.

Immunological analysis of plasminogen activators from cultured human cancer cells

Immunological similarities or differences between urokinase and plasminogen activators from 9 lines of cultured human cancer cells with varying degrees of fibrinolytic activity were examined with antibodies against human urokinase. The antibodies completely inhibited the fibrinolytic activity of 4 lines of gastric cancer, 2 lines of lung cancer, 1 line of urinary bladder cancer and 1 line of renal cancer, indicating that the plasminogen activators from these cell lines were immunologically identical to urokinase. In 5 out of these cell lines, immunological identity was also confirmed by double diffusion analysis. The plasminogen activator from 1 line of lung cancer was found to be immunologically dissimilar to urokinase by a neutralization experiment and double diffusion analysis. These findings indicate that there are at least two immunologically distinguishable forms of plasminogen activators from human cancer cells.

Immunoadsorbent affinity purification of the fifth component (C5) of human complement and development of a highly sensitive hemolytic assay

The fifth component of complement (C5) has been isolated from human serum in fully hemolytically active form by immunoadsorbent and anion exchange column chromatography. The immunoadsorbent column was prepared by the covalent coupling of the purified IgG fraction obtained from monospecific goat anti-human C5 antiserum to CNBr activated Sepharose 4B. Establishment of appropriate conditions for the dissociation and elution of functionally active C5 from the immunoadsorbent column was of central importance in the development of this purification procedure. The C5 preparations exhibited final yields of 20--50% with 570--710-fold purification factors based on recovery of specific hemolytic activity. These preparations were free of contaminating serum proteins as judged by SDS-polyacrylamide slab gel electrophoretic and immunochemical criteria. A C5-depleted reagent (C5D) was generated from the non-adsorbed protein containing fractions obtained subsequent to the passage of freshly drawn NHS plus 10 mM EDTA through the monospecific anti-C5 Sepharose 4B column. Upon reconstitution of C5D with Ca2+, Mg2+, and C1q, this reagent was utilized for the detection and quantitation of C5 hemolytic activity. The purified C5 preparations contained 1.5--2.5 x 10(12) effective molecules/mg protein and NHS expressed 0.5--2.0 x 10(11) effective molecules/ml.

Effects of human complement component 1 inactivator on neutrophil chemotaxis and chemotactic deactivation

This study was undertaken to ascertain the relationship between complement-derived chemotactic factors and complement component 1 inactivator (C1INA) enhancement of neutrophil chemotaxis. Studies were also designed to determine whether the C1s- reactive or binding site on C1INA was functional in altering chemotactic responsiveness of neutrophilic leukocyes. Chemotaxis was assessed by determining cell migration in micropore filters. C1INA was found to enhance the chemotactic response to zymosan-activated plasma, C5a, and N-formyl-L-methionyl-L-phenylalanine and to bring the response of chemotactically deactivated cells to normal. In contrast, C1INA inhibited the chemotactic response to trypsin and EAC4oxy2-activated C3. Complexes of C1INA and C1s- failed to mediate the usual C1INA-enhanced response. Artificially produced C5-deficient plasma, when treated with zymosan, failed to support chemotaxis or to produce chemotactic deactivation. C1INA was without effect when this activated plasma was used as a source of chemotactic factors. We conclude from these data that C1INA enhancement of neutrophil chemotaxis to activated plasma is associated with C5-derived chemotactic fragments. The effects of C1INA are apparently related to the C1s- reactive or binding site(s) on the C1INA molecule. We suggest that C1INA may play a homeostatic role in neutrophil chemotaxis.

Size increase induced in Walker ascites cells by chemotactic factors

Upon interaction with the tumor cell chemotactic factor derived from zymosan-activated serum or with the synthetic chemotactic factor, formylmethionyl-leucyl-phenylalanine (f-met-leu-phe), the number of Walker 256 carcinosarcoma cells in suspension dropped as measured by a Coulter Counter. The drop in the number of cells counted by the Coulter Counter was accompanied by and possibly attributed to a swelling in the mean cell volume of approx. 20%. These effects were blocked by the addition of 2-deoxy-d-glucose, along with the chemotactic factors, to the tumor cells. The doses of the chemotactic factors which induced these responses paralleled closely the doses which have been shown to induce a chemotactic response as measured in the Boyden Chamber assay. These findings indicate that non-leukocytic cells, like leukocytes, are capable of other responses in addition to chemotactic migration in the Boyden chamber assay upon interaction with appropriate chemotactic factors.

Biosynthesis of the complement components and the regulatory proteins of the alternative complement pathway by human peripheral blood monocytes

Short-term cultures of human peripheral blood monocytes were shown to synthesize the alternative pathway complement components C3, factors B (B) and D (D), and properdin, the regulatory proteins C3b inactivator (C3bINA) and beta 1H, in addition to C2, C4, and C5. B, D, properdin, C3bINA, and C2 were detected by functional assays, whereas beta 1H, C4, C3, and C5 could only be detected using immunochemical procedures. Immunoperoxidase localization studies showed that all the cells in each culture contained each component, so it is possible that all monocytes synthesize each component. It is concluded that cells of the monocyte-macrophage series form a mobile source of complement components and regulatory proteins which can be concentrated at sites of inflammation.

Thromboplastic and fibrinolytic activities in various organs of congenitally athymic nude mice

Thromboplastic and fibrinolytic activities in various organs of congenitally athymic nude mice were estimated. These activities varied from one organ to another and the organs were divided into six groups of possible combinations of these activities. The lung revealed high thromboplastic and high fibrinolytic activities, while the liver showed low thromboplastic and low fibrinolytic activities. The pattern of distribution of these activities in various organs of nude mice was almost similar to that of rats and mice with normal thymus. No plasmin activity was found in all organs.

C5 chemotactic fragment induces leukocyte production of tissue factor activity: a link between complement and coagulation

Complement-activated human plasma causes generation of tissue factor in human leukocytes. This phenomenon appears to be related to the fifth component of complement (C5) as demonstrated by the use of C5 deficient-plasma and suppression of activity with antibody to C5. Isolation of the chemotactic factor from activated serum or trypsinization of purified C5 reproduces the phenomenon. These data provide evidence for a direct link between complement products and activation of the coagulation system. Because chemotactic peptides from C5 can be generated by a variety of enzymes, our findings suggest a relationship between complement, coagulation, and inflammation.

The biochemistry of complement

Current biochemical studies of the complement system are illustrated by description of the activation of complement by the classical pathway after interaction with antibody aggregates. This is described in terms of the structures of the components involved, their assembly and the mechanism of activation.

Complement (C5-a)-induced granulocyte aggregation in vitro. A possible mechanism of complement-mediated leukostasis and leukopenia

Activated plasma complement will induce biphasic aggregation of human granulocytes dectable by standard nephelometric techniques. The responsible active component was suggested to be C5a by molecular weight and heat-stability assays; moreover, aggragating activity was ablated by anti-C5 but not anti-C3 antibodies. C5a prepared by trypsinization of purified C5 reproduced the aggregating activity of whole activated plasma, whereas plasma from a C5-deficient donor did not support aggregation. Embolization of granulocyte aggregates might be a previously unsuspected cause of leukostasis and pulmonary damage in various clinical situations where intravascular complement activation occurs.

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.

Human pancreatic carcinoma (MIA PaCa-2) in continuous culture: sensitivity to asparaginase

An undifferentiated human pancreatic carcinoma has been established in continuous culture and is grown in Dulbecco's modified. Eagle's medium fortified with 10% fetal calf serum and 2.5% horse serum. The established cell line (MIA PaCa-2) has a doubling time of 40 h. The cells are large with abundant cytoplasm, exhibit a high degree of aneuploidy and have a tendency to grow on top of other cells. MIA PaCa-2 grows in soft agar with a colony-forming efficiency of 19%. Both MIA PaCa-2 cells and a cell line from another pancreatic carcinoma obtained from National Cancer Institute (NCI) are sensitive to asparaginase, a property not shared by several other human tumor cell lines tested.