Independent and consecutive action of the complement components C5, C6 and C7 in immune hemolysis. I. Preparation of EAC1-5 with purified guinea pig C3 and C5

Absence of CD59 in Guinea Pigs: Analysis of the Cavia porcellus Genome Suggests the Evolution of a CD59 Pseudogene

CD59 is a membrane-bound regulatory protein that inhibits the assembly of the terminal membrane attack complex (C5b-9) of complement. From its original discovery in humans almost 30 years ago, CD59 has been characterized in a variety of species, from primates to early vertebrates, such as teleost fish. CD59 is ubiquitous in mammals; however, we have described circumstantial evidence suggesting that guinea pigs (Cavia porcellus) lack CD59, at least on erythrocytes. In this study, we have used a combination of phylogenetic analyses with syntenic alignment of mammalian CD59 genes to identify the only span of genomic DNA in C. porcellus that is homologous to a portion of mammalian CD59 and show that this segment of DNA is not transcribed. We describe a pseudogene sharing homology to exons 2 through 5 of human CD59 present in the C. porcellus genome. This pseudogene was flanked by C. porcellus homologs of two genes, FBXO3 and ORF91, a relationship and orientation that were consistent with other known mammalian CD59 genes. Analysis using RNA sequencing confirmed that this segment of chromosomal DNA was not transcribed. We conclude that guinea pigs lack an intact gene encoding CD59; to our knowledge, this is the first report of a mammalian species that does not express a functional CD59. The pseudogene we describe is likely the product of a genomic deletion event during its evolutionary divergence from other members of the rodent order.

Detection of two variants of complement component C3 in C3-deficient guinea pigs distinguished by the absence and presence of a thiolester

The complement system is an essential part of the innate defense, and C3 is an integral part of this powerful system. In previously identified complement C3 deficient guinea pigs only approx. 5% of the normal serum C3 level is detectable. No differences were found between in vitro C3 protein synthesis and C3 mRNA levels of cells from C3-deficient and wild-type animals and the amino acid sequences of both C3 proteins are identical as deduced from cDNA sequencing. Previously, the principal inability to form a C3 thiolester was discussed as a possible reason for this C3-deficiency. Here we report the isolation of two functionally different C3 species from the C3-deficient animals. Only one of these C3 proteins exhibits normal hemolytic activity and contains a thiolester group. The second C3 species is exclusively present in C3-deficient animals and lacks a thiolester, explaining its failure to express hemolytic activity. The presence of a second C3 species lacking a thiolester structure only in C3-deficient animals indicates that the stability of the thiolester may play a role in C3 deficiency. However further analysis of the in vitro stability of the thiolesters of C3 from normal and C3-deficient guinea pigs revealed no differences. A decreased in vivo thiolester stability might lead to the presence of C3 with and without a thiolester or alternatively the expression of two isoforms of C3 in these animals. Considering the central role of C3 in host defense, the mechanisms of C3 thiolester formation require further analysis.

Immunopotentiating compounds from Tinospora cordifolia

The active principles of Tinospora cordifolia a traditional Indian plant were found to possess anticomplementary and immunomodulatory activities. Syringin (TC-4) and cordiol (TC-7) inhibited the in vitro immunohaemolysis of antibody-coated sheep erythrocytes by guinea pig serum. The reduced immunohaemolysis was found to be due to inhibition of the C3-convertase of the classical complement pathway. However, higher concentrations showed constant inhibitory effects. The compounds also gave rise to significant increases in IgG antibodies in serum. Humoral and cell-mediated immunity were also dose-dependently enhanced. Macrophage activation was reported for cordioside (TC-2), cordiofolioside A (TC-5) and cordiol (TC-7) and this activation was more pronounced with increasing incubation times.

Anti-complement activity of oleanolic acid: an inhibitor of C3-convertase of the classical complement pathway

Oleanolic acid is a naturally occurring compound, isolated from Luffa cylindrica, which inhibits the in-vitro immunohaemolysis of antibody-coated sheep erythrocytes by guinea-pig serum. In further experiments this reduced immunohaemolysis was found to be due to inhibition of the C3-convertase of the classical complement pathway. The threshold concentration for inhibition of C3-convertase was 100 micrograms mL-1. However, higher concentrations of oleanolic acid showed constant inhibitory effects on immunohaemolysis. Oleanolic acid also exhibited weak inhibitory effects on individual components of the complement system.

Anticomplementary activity of boswellic acids--an inhibitor of C3-convertase of the classical complement pathway

Boswellic acids (BA), an anti-inflammatory and anti-arthritic principle/s of Boswellia serrata, were found to possess anticomplementary activity. It inhibits the in vitro immunohaemolysis of antibody-coated sheep erythrocytes by pooled guinea-pig serum. The reduced immunohaemolysis was found to be due to inhibition of C3-convertase of the classical complement pathway. The threshold concentration for inhibiting C3-convertase was found to be 100 micrograms. However, higher concentrations of BA showed constant inhibitory effects on immunohaemolysis. BA also exhibited weak inhibitory effects on individual components of the complement system. In vivo administration of BA also showed the inhibitory effect on guinea-pig serum.

Detection of native human complement components C3 and C5 and their primary activation peptides C3a and C5a (anaphylatoxic peptides) by ELISAs with monoclonal antibodies

Monoclonal antibodies (mAbs) were raised against human C3a, C3b, C5a, and C5b after immunization of BALB/c mice with the native components C3 and C5. Using different combinations of these mAbs we have developed four sensitive sandwhich-enzyme-linked immunosorbent assays (ELISAs) for the detection of native C3 or C5 in samples with low concentrations of these proteins, e.g., in cell culture supernatants or synovial fluids and cerebrospinal fluids (CSF) and for the detection of the anaphylatoxic peptides (AT-peptides) C3a or C5a in human EDTA-plasma. The C3- and C5-ELISAs were found to be specific for the uncleaved complement proteins. Two different anti-C3a or anti-C5a mAbs were combined for the C3a- and C5a-ELISA. Before assaying a sample in the C3a- or C5a-ELISA a precipitation step to eliminate uncleaved C3 and C5 was necessary. The sensitivity and specificity of the four ELISAs were tested with purified antigens and EDTA-plasma or Cobra venom factor-activated EGTA-plasma samples as a source of C3a and C5a. The detection limits were 1 ng/ml for C3, 1 ng/ml for C3a, 2 ng/ml for C5, and 100 pg/ml for C5a. Plasma samples from patients undergoing cardiopulmonary bypass (CPB) surgery were used as a source of pathological material.

Rosmarinic acid: a new inhibitor of complement C3-convertase with anti-inflammatory activity

Rosmarinic acid (RA) is a naturally occurring compound, isolated from Rosmarinus officinalis or Melissa officinalis which inhibits the in vitro immunohaemolysis of antibody-coated sheep erythrocytes by guinea pig serum. In further experiments this reduced immunohaemolysis was found to be due to inhibition of the C3-convertase of the classical complement pathway. The threshold concentration for inhibition of C3-convertase was 10(-6) mol/l. RA with an optimal inhibitory concentration between 5 and 10 mumol/l., resulting in about 70% inhibition of haemolysis. However, higher concentrations of RA were less effective at inhibiting C3-convertase. The inhibition may not be specific for C3-convertase, since another serine protease, elastase, was also weakly inhibited by RA in vitro. RA also exhibited inhibitory activity in three in vivo models in which complement activation plays a role. Thus, RA (0.316-3.16 mg/kg i.m.) reduced paw oedema induced by cobra venom factor (CVF) in the rat, and at 1-100 mg/kg p.o. inhibited passive cutaneous anaphylaxis in the rat. In addition, at 10 mg/kg i.m. RA impaired in vivo activation by heat-killed Corynebacterium parvum (i.p.) of mouse macrophages, as measured by the decreased capacity of the activated macrophages to undergo the oxidative burst. RA (0.1-10 mg/kg i.m.) did not inhibit t-butyl hydroperoxide-induced paw oedema in the rat, indicating selectivity for complement-dependent processes.

Inhibition of interleukin 3 function by a fragment of the third component of complement

A C3d-like (C3d-1) fragment of 33 kDa was isolated and its biological activity studied. The fragment was generated from guinea pig C3b by porcine pancreas kallikrein and purified by fast protein liquid chromatography. The C3d-like fragment inhibited interleukin (IL) 2-dependent T lymphocyte proliferation. The suppressive activity of the described C3d-1 fragment was not restricted to lymphocytes as targets but inhibited in addition the proliferation of a nonlymphocyte mast cell line which was strictly IL3-dependent in its proliferative capacity. Kinetic studies implied early stages of cellular proliferation to be influenced. Furthermore, the C3d-1 fragment was not only an inhibitor of cellular proliferation but was also a potent inducer of leukocytosis.

Mouse peritoneal macrophages cultured serum-free deposit complement on IgM-coated sheep erythrocytes in vitro

We conclude that the macrophages during cultivation produce the complement components of the classical pathway of complement, deposit complement components on EIgM and then phagocytose these cells via complement receptors. The conclusion is based on the following: EIgM, an activator of the classical pathway, are ingested when cultured serum-free with mouse peritoneal macrophages. We found a significantly higher binding of labelled protein to EIgM than to E kept in macrophage cultures in the presence of tritiated leucine, showing that de novo synthesis of macrophage-derived protein with affinity to EIgM takes place. A fraction of the bound protein is C3b and iC3b, since anti-mouse C3 antibodies bound to the co-cultured EIgM. Cycloheximide or anti-Mac-1 in the cultures inhibited macrophage attachment and uptake of EIgM. The phagocyte uptake of EIgM coated with complement by serum pretreatment was not inhibited by cycloheximide. This shows that the phagocytosis of the EIgM is dependent on erythrocyte-bound complement proteins made by the macrophage.

An inherited deficiency of the third component of complement, C3, in guinea pigs

Hereditary deficiency of the third component of complement, C3, is found very seldom in the human. C3 deficiency is associated with severe bacterial infections revealing the central role of C3 in complement activation via the classical or alternative pathway. We describe a new hereditary C3 deficiency in strain 2 guinea pigs. Serum from these animals had a markedly reduced lytic activity in a standard assay for complement-dependent, antibody-mediated cytotoxicity. In functional assays of individual components, the hemolytic activity of the components C4, C2, C5 and of factors B, D and H was in the normal range. The functional C3 titer, and similarly C3 antigenic activity in the serum of these C3-deficient animals (C3D) was on average only 5.7% of normal activity. Typing the animals with alloantisera or monoclonal antibodies to guinea pig Ia-antigens revealed that the C3D animals had the major histocompatibility complex-haplotype of inbred strain 2 guinea pigs (B.1, Ia.2,4). The C3 defect is not linked to the major histocompatibility complex and, in addition, is not linked to a C3a receptor deficiency. Macrophages and hepatocytes of the C3D animals have an unimpaired capacity for synthesis and secretion of C3 as measured by enzyme-linked immunosorbent assay. There was no indication for hypercatabolism of normal C3 by the animals as shown by plasma clearance of 125I-radiolabeled C3. Thrombocytes of the C3D animals responded normally to stimulation with purified C3a in an ATP-release assay without an indication for a desensitization in vivo. Possibly the fault resides in an enhanced susceptibility of their own C3 to proteolysis. However, C3 partially purified from the plasma of the C3D animals or secreted by hepatocytes exhibited no obvious structural differences to purified normal C3 in sodium dodecyl sulfate-polyacrylamide gel electrophoresis or in immunoblotting. The C3D serum had a reduced bactericidal activity compared to normal or to C4-deficient serum. Nevertheless, the animals are apparently healthy without an indication for increased frequency of bacterial infections. These guinea pigs provide an unique model for analysis of the biological functions of C3 in vivo and in vitro without the need for artificial C3-depletion procedures with all their known and unknown side-effects.

Hepatocellular carcinoma after thorotrast exposure: establishment of a new cell line (Mz-Hep-1)

A human hepatoma cell line, associated with thorotrast exposure, from an hepatitis B marker-negative patient was established as a permanent cell line (Mz-Hep-1) in tissue culture. Histology of the primary tumor, as well as phase contrast, transmission and scanning electron microscopy of the cultured cells showed typical characteristics of liver cells. Mz-Hep-1 cells secreted complement components (C2, C3, C4), carcinoembryonic antigen, lactate dehydrogenase, chymotrypsin, haptoglobin and retinol-binding protein and expressed HLA-, transferrin-, blood group B-related determinants and complement component C5 and carcinoembryonic antigen on their cell surface. Mz-Hep-1 cells represent the first human hepatoma cell line, which is strongly associated with a carcinogen.

Biosynthesis of the third (C3), eighth (C8), and ninth (C9) complement components by guinea pig hepatocyte primary cultures

In the present report guinea pig hepatocyte primary cultures were established in order to study the synthesis of the eighth (C8) and ninth (C9) complement component. As reference-protein, the third complement component (C3) was measured antigenetically and hemolytically. Synthesis of C8 and C9 was determined by means of the hemolytic activity of the culture supernatant harvested every 24 h during a 6-day incubation period in vitro. The data to be reported demonstrated that the hepatocytes are able to synthesize spontaneously and secrete C8 and C9; in their culture medium a hemolytic activity of about 15-25 X 10(8) em/10(6) cells/24 h for C8 and of 25-90 x 10(8) em/10(6) cells/24 h for C9 were found. The same hepatocyte cultures produced 2500-6000 micrograms/10(6) cells/24 h of C3. Hemolytic C3 activity was also found in the culture media. The synthesis of C8 and C9 could be reversibly inhibited by addition of 30-50 micrograms cycloheximide per ml of culture medium. The kinetics of synthesis show a slight decrease after the first day of culture and a recovery in the following days up to a rate that is two- to threefold higher than that of the first day. The data suggest that hepatocytes could contribute to the production of C8 and C9 present in the plasma.

The effect of ethylenedinitrilotetraacetic acid (EDTA) on the reaction between the guinea-pig C5 convertase and guinea-pig C5

Guinea-pig C5 was reacted with EAC1423 in the washed-cell intermediate assay in the presence of glucose gelatin veronal buffer (GGVB), Zn2+-GGVB (0.025 mM), GGVB2+ containing Ca2+ and/or Mg2+ or EDTA (0.013 M)-GGVB. The EDTA inhibited the formation of competent SAC14235, while Ca2+ and/or Mg2+ had a slight enhancing effect compared to GGVB alone and Zn2+ gave a four-fold increase. Similar results were obtained by using human C5 with guinea-pig C5 convertase and functionally pure guinea-pig C6, C7, C8 and C9. When guinea-pig C6 was incorporated into these various reaction mixtures with guinea-pig C5, its addition markedly reduced the inhibition by EDTA, while Zn2+ still showed an enhancing effect. These results demonstrate that EDTA inhibited formation of competent SAC14235 by preventing activation of C5. The association of C6 with C5 can partially overcome the inhibition of C5 conversion by EDTA and may account for C5 activity in reaction mixtures containing C-EDTA.

Quantitative studies of the secretion of complement component C3 by resident, elicited and activated macrophages. Comparison with C2, C4 and lysosomal enzyme release

To quantitate the secretion of complement component C3 by guinea pig peritoneal macrophages an enzyme-linked immunosorbent assay was developed. C3 secretion was studied in resident, elicited and activated macrophages and compared with release of hemolytically active C2 and C4, as well as the lysosomal enzyme beta-D-2-acetamido-2-deoxyglucosidase. Resident macrophages secreted about 6 ng C3/10(6) cells/h into culture supernatants over a period of 12 h. Corynebacterium parvum-activated cells were found to secrete 3 times that amount at nearly constant rates. There was a stepwise increase in secretion of functional C2 and C4 when comparing resident, elicited and activated macrophages; secretion was 2--4 times higher in activated than in resident cells.

Cartilage specific collagen activates macrophages and the alternative pathway of complement: evidence for an immunopathogenic concept of rheumatoid arthritis

We studied the effect of human interstitial collagen types I, II, and III on serum-free cultured mouse macrophages and on the complement classical and alternative pathways in human and guinea-pig serum. Type II collagen produced a dose-dependent consumption and conversion of C3 and factor B both in the homologous and in the heterologous system. This effect on the alternative pathway was reproduced in genetically C4-deficient guinea-pig serum and could be triggered by native, triple helical type II molecules, by their component alpha chains, and the CNBr peptide mixture. Addition of type II collagen to the mouse macrophage cultures induced not only a dose- and time-dependent secretion of lysosomal enzymes, but also the generation of a supernatant factor cytotoxic for mouse mastocytoma P 815 cells. Collagen of types I and III were conspicuously less active or inactive in all assays. The studies demonstrate properties of the collagen specific for cartilage which, on a molecular level, suggest its direct, local participation in the production and perpetuation of rheumatoid arthritis.

Low zone desensitization: a stimulus-specific control mechanism of cell response. Investigations on anaphylatoxin-induced platelet secretion

The biologic activity of the anaphylatoxic peptides C5a and C3a is regulated efficiently at the target-cell level by the phenomenon of desensitization. Desensitization of platelets is stimulus specific and can be induced by low concentrations of anaphylatoxins without any preceding secretory event. In contrast to activation to secretion, desensitization is Ca++ independent but much more time consuming, especially at lower temperatures where both processes differ markedly in reaction velocity. This low zone desensitization insures that secretion from platelets only occurs when high amounts of anaphylatoxins are rapidly generated in the vicinity of the target-cell. Consequently, stimulus-specific unresponsiveness of the target cells can be induced by slowly increasing the concentration of the respective stimuli in their vicinity. Cellular control seems to act as a first-line mechanism of regulation, whereas the role of fluid-phase control is considered as preventing longer persistence and systemic accumulation of active anaphylatoxins.

Activation of the alternative pathway of complement: efficient fluid-phase amplification by blockade of the regulatory complement protein beta1H through sulfated polyanions

Current concepts of activation of the alternative pathway of complement (APC) focus on the central role of an amplification mechanism triggered by C3b which is covalently bound to the surfact of activating substances. Using sulfated polyanions as model substances, an efficient fluid-phase activation of complement is demonstrated in contrast to solid-phase activation. It is shown that particulate high-molecular weight sulfated polyanions are capable of reversible binding the guinea pig and human regulatory protein beta1H. This fixation leads to an extensive activation of C3 and factor B because the regulatory function of beta1H is blocked in the fluid-phase C3b-dependent amplification system of the APC. Addition of beta1H-depleted C4-deficient guinea pig serum reconstitutes the physiological control mechanisms of the APC. Guinea pig beta1H, purified to homogeneity, is described as a 160000 dalton protein of a single-chain structure. In addition, highly specific and sensitive test systems for beta1H are described.

The role of complement in the function of the monocyte - macrophage system

In parallel to the behavior of many agents that activate complement via the alternative pathway and can stimulate macrophages to secrete lysosomal enzymes we investigated the interaction of mouse peritoneal macrophages cultured in a serum-free medium with various stimuli such as zymosan, polyanions, collagen type II, and immune complexes prepared from tetanus toxoid and pooled human anti-tetanus toxoid F(ab)2. All these stimuli induced the release of hydrolytic enzymes from macrophage in culture. The release was time and dose dependent and is not associated with loss of the cytoplasmic enzyme lactate dehydrogenase or any other sign of cell death. The mechanism of macrophage activation by these various agents is unknown. Macrophages have surface receptors for Fc and C3b with the capacity to bind immune complexes or C3b, respectively, and this is followed by activation of the cells. Activation via the Fc part can be excluded in these experiments. The possibility therefore arose that macrophages might be stimulated by endogenous C3 via the C3b receptor, since it is known that all the substances mentioned above can activate C3. To confirm this hypothesis we tried to inhibit this reaction by using an anti-C3-Fab preparation. There was hardly any detectably enzyme release after adding the anti-C3-Fab (dose dependent) together with the various stimuli to the macrophages. An unrelated Fab preparation showed no inhibitory effect. Furthermore, incubation of macrophages and the stimuli together with beta 1H and C3bINA abolished the effect to activate the macrophages. The observations now presented focus attention to the possibility that endogenous C3 could play a role in the stimulation of mouse peritoneal macrophages by various activators of the alternative pathway.

Activation of the alternative pathway of complement by mycobacteria and cord factor

The ability of a number of mycobacteria and some of their components to activate complement was examined. Mycobacterium bovis BCG (Glaxo strain), Mycobacterium leprae, Mycobacterium lepraemurium, and cord factor activated the alternative pathway of complement in normal human serum and normal and C4-deficient guinea pig sera and generated biologically active products. BCG (Pasteur strain) and muramyl dipeptide did not activate complement. The relevance of activation of complement by mycobacteria to their induction of granulomas is discussed.

Cytolysis of fibroblasts by C3a

C3a was found to be more cytolytic to transformed than to primary fibroblast cultures from mouse and man. Fibroblasts made quiescent with caffeine were lysed by the same concentrations of C3a as untreated cells. These findings may have implications in tumour immunity.

Use of C6- and C7-deficient human sera in quantitative hemolytic assays for C6 and C7

Quantitative hemolytic assays for C6 and C7 using as R reagents sera from patients deficient in these components are described. The assays gave linear results. Normal range for serum C6 was found to be 21,400--41,700 C6 hemolytic units/ml; for serum C7 the normal range was 5540--9860 C7 hemolytic units/ml.

Platelet activation: a new biological activity of guinea-pig C3a anaphylatoxin

3H-serotonin-release from labelled gp-platelets is established as a sensitive method for testing a new biological activity of gp-C3a anaphylatoxin in an autologous situation. Time-, dose- and temperature-dependent release reactions as well as specific inhibition by carboxypeptidase B and anti-C3a antibodies show that C3a is a potent and specific inducer of platelet activation. Inactive C3a does not induce 3H-serotonin-release but specifically inhibits the action of C3a on platelets.

Studies on C3 convertases. Inhibition of C5 convertase formation by peptides containing aromatic amino acids

The influence of various peptides containing the aromatic amino acids phenylalanine and tyrosine on the formation of the enzyme EAC1423 of the complement system from component C3 and enzyme EAC142 was investigated. Kinetic analysis of enzyme EAC1423 formation and studies on the binding of the C3b fragment of 125I-labelled component C3 to enzyme EAC142 both showed that binding of the C3b fragment of component C3 was decreased by the peptides. Kinetic studies on component-C3 turnover in the fluid phase of enzyme EAC142 failed to reveal effects of the peptides. However, an initial lag in component-C3 turnover occurred that at constant component-C3 concentration was inversely proportional to enzyme EAC142 concentration. This lag in enzyme EAC142 activity is considered as an indication that the interaction of enzyme EAC142 with component C3 possibly does not follow simple Michaelis-Menten kinetics, as was previously assumed. It is shown that the stages after enzyme EAC1423 formation are not influenced by the peptides, suggesting a high degree of specificity of the peptides for the inhibition of enzyme EAC1423 formation.

Antibodies to Acholeplasma laidlawii membrane lipids in normal guinea pig serum

Acholeplasma laidlawii is killed and lysed by fresh normal guinea pig serum (GPS) without additional antibodies. Prior incubation of GPS with whole A. laidlawii organisms abolishes the killing activity of GPS. In the present study it was demonstrated that antibodies are present in normal GPS. The classical pathway, not the alternative pathway, of the complement sequence was activated by these antibodies in fresh normal GPS. The antibodies in GPS belong to the IgG class of immunoglobulins. They are directed predominantly against the membrane phospholipids of A. laidlawii. These antibodies may be induced either by natural infection of guinea pigs with A. laidlawii or by antigenic determinants of other microorganisms of food antigens.

Biosynthesis of pro-C3, a precursor of the third component of complement

A precusor of the third component of complement, pro-C3, was detected in studies of cell-free synthesis and intracellularly in homogenates of liver tissue cultures. The molecular weight of pro-C3 was indistinguishable from that of intact native C3 secreted in vitro by liver or peritoneal macrophages, but its structure was different. Pro-C3 is a single polypeptide chain, whereas C3 secreted by cells in culture consists of two polypeptide chains (mol wt 120,000 and 76,000) linked by disulfide bonds.

Cytolytic effects of the complement cleavage product, C3a

Purified C3a, a cleavage product of the third component of complement,was incubated with various cell types of human and mouse origin. All the tumour cell types tested were lysed by low concentrations of C3a, whereas normal human lymphocytes were relatively resistant. No lysis was produced by C3 or C3b. The possible role of C3a in immunity against tumours is discussed.

Activation of complement by the alternative pathway as a factor in the pathogenesis of periodontal disease

Dental plaque and a bacterium, Actinomyces viscosus, isolated from plaque that can reproduce periodontal disease in germ-free rats, are activators of complement by the alternative pathway. It is suggested that this process is involved in the pathogenesis of chronic inflammatory periodontal disease.

In vitro synthesis of factor B of the alternative pathway of complement activation by mouse peritoneal macrophages

Factor B of the alternative pathway of complement activation was shown to be synthesized and secreted by unstimulated mouse peritoneal macrophages. The activity of B in the culture supernatants from macrophage monolayers was detected by consumption of C3 in reaction mixtures containing supernatant and guinea pig factors C3, D and insoluble C3b. Using a monospecific antiserum, factor B in concentrated culture supernatants was shown by immunodiffusion and immunoelectrophoresis to be identical to factor B in mouse plasma and to form a characteristic complex with cobra venom factor in the presence of D. A steady rate of factor B secretion was observed for 4 days providing the medium was changed every 24 h. Cycloheximide (0.5 mug/ml), an inhibitor of protein synthesis, caused inhibition (90%) of factor B production. Incubation of culture medium containing 14C-labeled amino acids with the macrophage monolayer resulted in incorporation of radioactivity into factor B as detected by autoradiography of precipitation lines formed with anti-B antiserum; This indicated that synthesis of factor B had occurred. In the same culture supernatants the presence of newly synthesized C3 was also demonstrated.

Interactions between Mycoplasma pneumoniae and guinea pig complement

The "toxic" effect of guinea pig serum (GPS) on Mycoplasma pneumoniae cells was tested under various conditions, using rounding and killing of the cells as test systems. Both activities could be inhibited by heat inactivation (56 C, 30 min). Killing required both Ca2+ and Mg2+, rounding only Mg2+. Both activities were temperature dependent and no rounding or killing occurred at 4C. Incomplete complement sequences with natural of artificial defects in C1, C4, or C6 resulted in lost or reduced killing. The rounding activity was only slightly affected. Anti-C3 antiserum blocked both phenomena; incubation of GPS with 10 mg of inulin per ml reduced the rounding activity, and the same treatment of GPS deficient in C4 inhibited rounding totally. Properdin factor D was shown to be necessary for rounding by GPS, with defects in either C1 or C4. By immune adherence bound C3b could be demonstrated on M. pneumoniae cells after GPS treatment, no antibodies against M. pneumoniae could be found in GPS by immune fluorescence. The results give evidence for complement being the toxic factor in GPS. Efficient killing requires the intact complement sequence. Furthermore, M. pneumoniae cells are able to activate the alternate pathway of complement. Activation of this pathway results in rounding of the cells, which are partly able to recover after this reaction. Biological consequences for the mycoplasmas are death or damage and possibly opsonization, even in the absence of specific antibodies. The host, too, is possibly affected by products of the reaction. The interaction of M. pneumoniae and complement could be involved in the early stages of the development of M. pneumoniae disease.

Complement-dependent B-cell activation by cobra venom factor and other mitogens?

It has been proposed that two distinct signals are required for the triggering of the precursors of antibody-forming bone marrow-derived cells (B cells): (a) the binding of antigen or of a mitogen to the corresponding receptor sites on B-cell membranes and (b) the interaction of activated C3 with the C3 receptor of B lymphocytes. There is growing evidence that B-cell mitogens and T (thymus-derived cell)-independent antigens are capable of activating the alternate pathway of the complement system (bypass). Therefore, the effect of another potent bypass inducer was investigated with regard to B-cell activation and the role of C3. Purified, pyrogen-free cobra venom factor was mitogenic for both T and B lymphocytes (cortisone-resistant mouse thymus cells and lymph node lymphocytes from congenitally athymic mice). Venom factor could substitute for T cells by restoring the potential of antibody formation to sheep red blood cells in mouse B-cell cultures supplemented with macrophages or 2-mercaptoethanol. Venom factor may be capable of conferring activated C3 to the C3 receptor of B lymphocytes: preincubation of lymphoid cells with homologous serum or plasma, 10 mM EDTA, and sepharose-coupled venom factor converted with serum to an enzyme active against C3, inhibited their capacity to subsequently form rosettes with sheep erythrocytes sensitized with amboceptor and C5-deficient mouse complement. In the absence of EDTA, preincubation of freshly prepared B-cell suspensions with C3-sufficient homologous serum also blocked their subsequent interaction with complement-sensitized erythrocytes and at the same time rendered them reactive to an otherwise T-cell-specific mitogen. Moreover, mitogen induced B-cell proliferation in lymph node (but not in spleen) cell cultures, appeared to depend on the availability of exogenous C3: zymosan-absorbed fetal bovine serum (only 8.3% site-forming units remaining) supported T-cell activation by phytohemagglutinin, concanavalin A, and venom factor, but failed to sustain B-cell stimulation by pokeweed mitogen, lipopolysaccharide, and venom factor. T-cell-dependent antibody formation in composite cultures containing T cells or T-cell-substituting B-cell mitogens, B cells, and macrophages, always required the presence of C3-sufficient serum.