Estimation of classical pathway of mouse complement activity by use of sensitized rabbit erythrocytes

Enhancement of the blood-circulation time and performance of nanomedicines via the forced clearance of erythrocytes

The rapid elimination of nanoparticles from the bloodstream by the mononuclear phagocyte system limits the activity of many nanoparticle formulations. Here, we show that inducing a slight and transient depletion of erythrocytes in mice (~5% decrease in haematocrit) by administrating a low dose (1.25 mg kg^-1) of allogeneic anti-erythrocyte antibodies increases the circulation half-life of a range of short-circulating and long-circulating nanoparticle formulations by up to 32-fold. Treatment of the animals with anti-erythrocyte antibodies significantly improved the targeting of CD4⁺ cells in vivo with fluorescent anti-CD4-antibody-conjugated nanoparticles, the magnetically guided delivery of ferrofluid nanoparticles to subcutaneous tumour allografts and xenografts, and the treatment of subcutaneous tumour allografts with magnetically guided liposomes loaded with doxorubicin and magnetite or with clinically approved 'stealthy' doxorubicin liposomes. The transient and partial blocking of the mononuclear phagocyte system may enhance the performance of a wide variety of nanoparticle drugs.

Crucial role of the terminal complement complex in chondrocyte death and hypertrophy after cartilage trauma

OBJECTIVE

Innate immune response and particularly terminal complement complex (TCC) deposition are thought to be involved in the pathogenesis of posttraumatic osteoarthritis. However, the possible role of TCC in regulated cell death as well as chondrocyte hypertrophy and senescence has not been unraveled so far and was first addressed using an ex vivo human cartilage trauma-model.

DESIGN

Cartilage explants were subjected to blunt impact (0.59 J) and exposed to human serum (HS) and cartilage homogenate (HG) with or without different potential therapeutics: RIPK1-inhibitor Necrostatin-1 (Nec), caspase-inhibitor zVAD, antioxidant N-acetyl cysteine (NAC) and TCC-inhibitors aurintricarboxylic acid (ATA) and clusterin (CLU). Cell death and hypertrophy/senescence-associated markers were evaluated on mRNA and protein level.

RESULTS

Addition of HS resulted in significantly enhanced TCC deposition on chondrocytes and decrease of cell viability after trauma. This effect was potentiated by HG and was associated with expression of RIPK3, MLKL and CASP8. Cytotoxicity of HS could be prevented by heat-inactivation or specific inhibitors, whereby combination of Nec and zVAD as well as ATA exhibited highest cell protection. Moreover, HS+HG exposition enhanced the gene expression of CXCL1, IL-8, RUNX2 and VEGFA as well as secretion of IL-6 after cartilage trauma.

CONCLUSIONS

Our findings imply crucial involvement of the complement system and primarily TCC in regulated cell death and phenotypic changes of chondrocytes after cartilage trauma. Inhibition of TCC formation or downstream signaling largely modified serum-induced pathophysiologic effects and might therefore represent a therapeutic target to maintain the survival and chondrogenic character of cartilage cells.

In Vitro and In Vivo Differences in Murine Third Complement Component (C3) Opsonization and Macrophage/Leukocyte Responses to Antibody-Functionalized Iron Oxide Nanoworms

Balancing surface functionalization and low immune recognition of nanomedicines is a major challenge. Opsonization with the third component of the complement protein (C3) plays a major role in immune cell recognition of nanomedicines. We used dextran-coated superparamagnetic iron oxide nanoworms (SPIO NWs) to study the effect of surface functionalization on C3 opsonization in mouse serum and subsequent macrophage/leukocyte recognition in vitro as well as on intravenous injection into mice. Previously, we found that in mouse serum, SPIO NWs became opsonized with C3 via complement lectin pathway. Crosslinking the dextran shell with epichlorohydrin significantly decreased C3 opsonization and uptake by mouse peritoneal macrophages. Crosslinked nanoworms (NWs) further functionalized with polyethylene glycol (PEG) or with PEG-antibody (Ab) (~160 IgG molecules/particle) did not show an increase in C3 opsonization and peritoneal macrophage uptake in vitro. Following tail vein injection into mice, plain crosslinked NWs and PEGylated crosslinked NWs showed very low C3 opsonization and mouse leukocyte uptake. However, Ab-decorated crosslinked NWs showed significant C3 opsonization and high level of complement-dependent uptake by leukocytes in mice. Decreasing the number of conjugated Abs to 46 IgG molecules/particle significantly reduced C3 opsonization and leukocyte uptake. Using fresh mouse lepirudin plasma rather than serum showed better correlation with C3 opsonization in vivo. The reason for this difference could be related to the known instability of complement classical pathway in mouse sera. Our data illustrate that fine-tuning in nanoparticle surface functionalization with Abs is required to avoid excessive complement activation and complement-mediated immune uptake in mice, and raise issues with in vitro immunological assays of nanomedicines intended to mimic in vivo conditions.

Biocompatibility of Biopolymers

This study examines the biocompatibility of two different syn thetic copolymers; a water soluble copolymer based on [N-(2-hydroxypropyl) methacrylamide] (HPMA) and an insoluble polymer based on 2-hydroxyethyl methacrylate (HEMA). Activation of classical and alternative complement pathways, phagocytic function, bone marrow status, and humoral immune re sponses were assessed after long-term application of the copolymers to mice of the C57BL/10ScSn strain. Histological examination was also performed on sec tions of liver, spleen and kidney. Our results indicate that a total dose of 2 g of HPMA copolymer/1 kg of body weight and 2.5 x 109 particles/mouse of HEMA microspheres did not affect any of the immune parameters that were studied.

Purification and characterization of human and mouse complement C3

Complement component C3 is the most abundant complement protein in plasma, central to all three complement activation pathways and essential to complement amplification. Thus, it is one of the most extensively studied complement proteins. This chapter describes the purification of C3 from human and mouse plasma using protein precipitation, followed by classical ion exchange chromatography and gel filtration. The biochemical and functional characteristics of the purified C3 are typically assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and hemolysis assays. The hemolysis assay is a standard technique to assess complement activity monitoring the lysis of red blood cells.

Functions of the complement components C3 and C5 during sepsis

Activation of the complement system is a key event in the pathogenesis of sepsis. Nevertheless, the exact mechanisms remain inadequately understood. In the current study, we examined the role of complement C3 and C5 in sepsis in wild-type and C3- or C5-deficient mice induced by cecal ligation and puncture. When compared to wild-type mice, C5(-/-) showed identical survival, and C3(-/-) presented significantly reduced survival. Interestingly, this was associated with significant decreases in plasma levels of proinflammatory mediators. Moreover, although septic C3(-/-) animals displayed a 10-fold increase of blood-borne bacteria, C5(-/-) animals exhibited a 400-fold increase in bacteremia when compared to wild-type mice. These effects were linked to the inability of C5(-/-) mice to assemble the terminal membrane attack complex (MAC), as determined by complement hemolytic activity (CH-50). Surprisingly, although negative control C3(-/-) mice failed to generate the MAC, significant increases of MAC formation was found in septic C3(-/-) mice. In conclusion, our data corroborate that hemolytic complement activity is essential for control of bacteremia in septic mice. Thus, during sepsis, blockade of C5a or its receptors (rather than C5) seems a more promising strategy, because C5a-blockade still allows for MAC formation while the adverse effects of C5a are prevented.

Extravasations and emigration of neutrophils to the inflammatory site depend on the interaction of immune-complex with Fcgamma receptors and can be effectively blocked by decoy Fcgamma receptors

Extravasation and emigration of neutrophils to the site of inflammation are essential early steps in the initiation of many antibody-mediated autoimmune diseases. The Fc domains of cell bound autoantibodies or immune-complexes (IC) are capable of triggering the neutrophil emigration via complement and FcgammaRs-mediated mechanisms. To define the clinical relevance and the relative contribution of these 2 pathways in IC-mediated neutrophil emigration, we have neutralized the FcgammaR-binding activity of IC with a recombinant dimeric Fc receptor, CD16A-Ig, and investigated the early events of IC-induced inflammation in mice. Systemic administration of purified CD16A-Ig blocked IC-induced inflammation, mast- cell degranulation, and extravasation of neutrophils in a reversed Arthus reaction. Although the binding of CD16A-Ig to IC did not alter the complement-activating properties of IC, no evidence for complement-dependent neutrophil emigration was observed. These results suggest that interaction of IC with cells expressing FcgammaRs at the inflammatory site results in the secretion of chemoattractants, which mediate complement-independent emigration of neutrophils in this cutaneous acute inflammation model. Furthermore, blocking the interaction of IC to FcgammaRs expressed on inflammatory cells by administering high-avidity Fc fusion dimers of low-affinity FcgammaRs is an effective way of preventing IC-induced acute inflammation in autoimmune diseases.

Deficiency of the mouse complement regulatory protein mCd59b results in spontaneous hemolytic anemia with platelet activation and progressive male infertility

Basal complement activity presents a potential danger for "self" cells that are tightly protected by complement regulators including CD59. Mice express two Cd59 genes (mCd59a and mCd59b); mCd59b has approximately a 6-fold higher specific activity than mCd59a. Consistently, mCd59b knockout mice present a strong phenotype characterized by hemolytic anemia with increased reticulocytes, anisopoikilocytosis, echinocytosis, schistocytosis, free hemoglobin in plasma, hemoglobinuria with hemosiderinuria, and platelet activation. Remarkably, mCd59b(-/-) males express a progressive loss of fertility associated with immobile dysmorphic and fewer sperm cells after 5 months of age. This work indicates that mCd59b is a key complement regulator in mice and that CD59 is critical in protecting self cells; it also provides a novel model to study complement regulation in human diseases.

Improved innate immunity of endotoxin-tolerant mice increases resistance to Salmonella enterica serovar typhimurium infection despite attenuated cytokine response

During infection with gram-negative bacteria, exposure of immune cells to lipopolysaccharide (LPS) from the bacterial cell membrane induces a rapid cytokine response which is essential for the activation of host defenses against the invading pathogens. Administration of LPS to mice induces a state of hyporesponsiveness, or tolerance, characterized by reduced cytokine production upon subsequent LPS challenge. In the model of experimental Salmonella enterica serovar Typhimurium infection of mice, we assessed the question of whether complete LPS tolerance induced by repetitive doses of LPS interfered with cytokine production and host defense against gram-negative bacteria. Although production of various cytokines in response to serovar Typhimurium was attenuated by LPS pretreatment, LPS-tolerant mice showed improved antibacterial activity, evidenced by a prolongation of survival and a continuously lower bacterial load. We attribute this protective effect to three independent mechanisms. (i) Peritoneal accumulation of leukocytes in the course of LPS pretreatment accounted for enhanced defense against serovar Typhimurium during the first 6 h of infection but not for decreased bacterial load in late-stage infection. (ii) LPS-tolerant mice had an increased capacity to recruit neutrophilic granulocytes during infection. (iii) LPS-tolerant mice showed threefold-increased Kupffer cell numbers, enhanced phagocytic activity of the liver, and strongly improved clearance of blood-borne serovar Typhimurium. These results demonstrate that despite attenuated cytokine response, acquired LPS tolerance is associated with enhanced resistance to infections by gram-negative bacteria and that this effect is mainly mediated by improved effector functions of the innate immune system.

Anti-inflammatory activities of Trichilia glabra aqueous leaf extract

Trichilia glabra L. aqueous leaf extract exerted a significant antiinflammatory effect 'in vivo' in the zymosan-induced inflammation model. The extract impaired the 'in vitro' activities of polymorphonuclear leukocytes and complement, components of mouse immune system closely related to the inflammatory response induced by zymosan. In particular, a significant reduction in the phagocytic capability and respiratory burst response of mouse polymorphonuclear leukocytes together with an inhibition in the hemolytic activity of mouse complement was observed.

Resistance to both complement activation and phagocytosis in type 3 pneumococci is mediated by the binding of complement regulatory protein factor H

To study the role of surface-associated proteins in the virulence of Streptococcus pneumoniae, we used two serotype 3 strains, ATCC 6303 and WU2, and two PspA-negative mutants of WU2, an encapsulated one, JY1123 (Caps(+)/PspA(-)), and an unencapsulated one, DW3.8 (Caps(-)/PspA(-)). ATCC 6303 and WU2 were highly virulent in mice, while the virulence of JY1123 was slightly decreased (50% lethal doses [LD(50)s], 24, 6, and 147 CFU/mouse, respectively); DW3.8 was avirulent (LD(50), 2 x 10(8) CFU). In vitro, ATCC 6303, WU2, and JY1123 (Caps(+)/PspA(-)) strongly resisted complement activation and complement-dependent opsonophagocytosis, whereas DW3.8 (Caps(-)/PspA(-)) was easily phagocytized in fresh serum. Trypsin treatment of ATCC 6303, WU2, and JY1123 (Caps(+)/PspA(-)) resulted in enhanced complement activation and complement-dependent opsonophagocytosis. Trypsin had no deleterious effect on the polysaccharide capsule. In addition, trypsin pretreatment of ATCC 6303 strongly reduced virulence upon intraperitoneal challenge in mice. This indicated that surface proteins play a role in the resistance to complement activation and opsonophagocytosis and contribute to the virulence of type 3 pneumococci. In subsequent experiments, we could show that the modulation of complement activation was associated with surface components that bind complement regulator factor H; binding is trypsin sensitive and independent of prior complement activation. Immunoblotting of cell wall proteins of the virulent strain ATCC 6303 with anti-human factor H antibody revealed three factor H-binding proteins of 88, 150, and 196 kDa. Immunogold electron microscopy showed a close association of factor H-binding components with the outer surface of the cell wall. The role of these factor H-binding surface proteins in the virulence of pneumococci is interesting and warrants further investigation.

Selection of a C5a Receptor Antagonist from Phage Libraries Attenuating the Inflammatory Response in Immune Complex Disease and Ischemia/Reperfusion Injury

A C5a-receptor antagonist was selected from human C5a phage display libraries in which the C terminus of des-Arg74-hC5a was mutated. The selected molecule is a competitive C5a receptor antagonist in vitro and in vivo. Signal transduction is interrupted at the level of G-protein activation. In addition, the antagonist does not cause any C5a receptor phosphorylation. Proinflammatory properties such as chemotaxis or lysosomal enzyme release of differentiated U937 cells, as well as C5a-induced changes in intracellular Ca2+ concentration of murine peritoneal macrophages, are inhibited. The in vivo efficacy was evaluated in three different animal models of immune complex diseases in mice, i.e., the reverse passive Arthus reaction in the peritoneum, skin, and lung. The i.v. application of the C5a receptor antagonist abrogated polymorphonuclear neutrophil accumulation in peritoneum and markedly attenuated polymorphonuclear neutrophil migration into the skin and the lung. In a model of intestinal ischemia/reperfusion injury, i.v. administration of the C5a receptor antagonist decreased local and remote tissue injury: bowel wall edema and hemorrhage as well as pulmonary microvascular dysfunction. These data give evidence that C5a is an important mediator triggering the inflammatory sequelae seen in immune complex diseases and ischemia/reperfusion injury. The selected C5a receptor antagonist may prove useful to attenuate the inflammatory response in these disorders.

Sex-limited protein: in vitro and in vivo functions

Mouse complement component C4 exists in two isoforms, C4 and a protein with expression restricted to male animals called sex-limited protein (Slp). Although Slp is about 95% homologous to C4, it is generally believed to be non-functional, at least in conventional haemolytic complement assays. In a previous study, however, we showed that Slp is haemolytically active in a C1-inhibitor (C1INH)-regulated, EDTA-resistant mouse complement activation pathway. To study other possible implications of this finding, we generated constitutively expressing Slp-transgenic mice. The transgene was crossed into otherwise Slp-deficient C57Bl/6J and NZB mice. Members of the third backcross generation of C57Bl/6J mice were tested for functional Slp and classical and alternative complement pathway activities (CH50 and AP50 levels, respectively). Slp-transgenic C57Bl/6J mice showed enhanced CH50, but normal AP50 levels when compared with non-transgenic littermates. To discover a possible protective role for Slp in spontaneous systemic lupus erythematosus (SLE) in NZBxNZW (NZBxW) mice, the third backcross generation of Slp-transgenic NZB mice was mated with NZW mice and the development of SLE in the female offspring was followed. In these introductory experiments, Slp-transgenic NZBxW animals presented with a significantly extended life span. Our results imply that Slp is a mouse complement component with functions which partially resemble some of those of human C4A.

Cutting Edge: Fc Receptor Type I for IgG on Macrophages and Complement Mediate the Inflammatory Response in Immune Complex Peritonitis

The contributions of Fc receptors (FcRs) for IgG (FcγRs) and complement to immune complex (IC)-mediated peritonitis were evaluated in BALB/c-, C57BL/6-, FcRγ chain-, and FcR type III for IgG (FcγRIII)-deficient mice, backcrossed to the C57BL/6 background. In BALB/c mice, but not in C57BL/6 mice, neutrophil migration was markedly attenuated after complement depletion. In mice lacking FcRγ chain, neutrophil migration was abolished, whereas it was unaffected in FcγRIII-deficient mice. Huge amounts of TNF-α (TNF) were found in the peritoneal exudate of BALB/c and C57BL/6 mice but were absent in mice lacking FcRγ chain or FcγRIII. Surprisingly, a functional inhibition of TNF in BALB/c and C57BL/6 mice had no effect on neutrophil infiltration. These data provide evidence that in IC peritonitis, the activation of FcR type I for IgG on peritoneal macrophages and the activation of the complement cascade, but not the interaction of ICs with FcγRIII and the subsequent release of TNF, initiate the inflammatory response in BALB/c and C57BL/6 mice.

The complement system of the marsupial Monodelphis domestica

The activation requirements and pathways of the serum C' system of the marsupial Monodelphis domestica were characterized using standard hemolytic procedures. The existence of distinct classical and alternative activation pathways was established on the basis of their ionic requirements, hemolytic capacity at different temperatures, kinetics of hemolysis, and differential susceptibility to the classical pathway inhibitor carrageenan. For the most part, the activities of these pathways were influenced by factors and conditions in a manner similar to the way they affect the activity of eutherian complement. These observations provide further support for the idea that Monodelphis domestica would serve as a useful model for comparative immunological studies in mammals.

Immunomodulatory activities of Cedrela lilloi and Trichilia elegans aqueous leaf extracts

The effects of Cedrela lilloi and Trichilia elegans (Meliaceae) aqueous leaf extracts on several parameters of the mouse immune system were studied. Both extracts showed a strong anticomplementary activity and inhibited the phagocytosis of opsonized sheep erythrocytes and the activation of the oxidative metabolism by opsonized zymosan on peritoneal macrophages. The in vitro proliferation of spleen T-lymphocytes was also impaired. Furthermore, treatment of mice with the extracts diminished the delayed-type hypersensitivity response to sheep erythrocytes. These results suggest that both extracts exert a marked immunomodulatory effect on the mouse immune system.

Impaired IgG-dependent anaphylaxis and Arthus reaction in Fc gamma RIII (CD16) deficient mice

The family of receptors for IgG (Fc gamma R) plays an essential role in antibody-mediated effector functions of the immune system. However, the specific contribution of each of the Fc gamma R classes to in vivo immune reactions is still unclear. Here, we demonstrate that mice deficient for the ligand-binding alpha chain of Fc gamma RIII lack NK cell-mediated antibody-dependent cytotoxicity and phagocytosis of IgG1-coated particles by macrophages. Strikingly, these mice lack IgG-mediated mast cell degranulation, are resistant to IgG-dependent passive cutaneous anaphylaxis, and exhibit an impaired Arthus reaction. These results indicate a prominent role for Fc gamma RIII in inflammatory and anaphylactic responses, making this receptor a potential target in immunotherapy.

C1-inhibitor prevents PEG fractionation-induced, EDTA-resistant activation of mouse complement

Fractionation of mouse serum by precipitation with a critical amount of polyethylene glycol 6000 (PEG; 11% w/v) results in a classical and alternative pathway-independent activation of the terminal complement route. The activation can take place after the separation of an activating principle together with the terminal route components from a natural regulator. The isolation and identification of the regulatory component preventing this activation in serum, is subject of this paper. The regulator was purified by fractionated PEG-precipitation (15-25%), followed by heparin-Sepharose affinity, Mono Q anion-exchange, and Superose 12 gel filtration chromatography. The regulator appeared to be a single-chain protein with a Mr of 96 k. A protein with similar activity purified from human serum had a Mr of 104 k and was functionally and antigenically indistinguishable from C1-INH. The mouse 96 k protein inhibited C1-esterase activity indicating that this protein is indeed C1-INH. Mouse C1-INH regulates the PEG fractionation-induced bypass activation of complement, but does not interfere with the assembly or the lytic activity of membrane attack complexes. alpha 2-Macroglobulin appeared also to be capable of inhibiting the PEG-precipitation-induced activation process, but with lower efficiency.

Rapid isolation of human complement component C9 to verify the specificity of a haemolytic C9 microassay

A sensitive, haemolytic microassay of human complement component C9 was developed. The assay is based on the principle of reactive (C5b6-initiated) haemolysis and uses commercially available C9-depleted serum as reagent for C9. The specificity of the assay was verified by rapid, activity-guided isolation of the haemolytic component from human serum using high-performance liquid chromatography (HPLC) on a system for fast protein liquid chromatography. This isolation yielded a single component with characteristics of C9. The results suggest that rapid, activity-guided isolation as a new application of HPLC can be a useful tool to demonstrate the specificity of a functional assay.

Effects of protein intake on immune parameters in mice surviving streptococcal infection

Groups of mice were fed for 2 weeks on isocaloric diets containing 5, 7, 20 and 40% (w/w) casein, respectively, then injected intraperitoneally with group B streptococci, and observed for their survival rates. The mice fed 7% or 20% casein had lower mortalities than those fed 5% or 40% casein. In order to explain the different survival rates, other groups of mice were fed on the experimental diets and examined for the number of leukocytes in the blood, of spleen cells and thymocytes, for IgG and IgM antibody titres to the streptococci, for haemolytic titres of sera, the amount of complement component 3 (C3), for chemiluminescence and opsonic activity of peritoneal exudate cells (PEC) and spleen cells (SP), production of superoxide anion from PEC and SP, and production of immunoglobulins from cultured SP. After 2 weeks on a 7 or 20% casein diet mice showed increased serum levels of IgM antibodies reactive with the whole bacterial cells on days 3-5 when they were immunised with a sublethal dose of group B streptococci. The mice fed on the 7% casein diet also showed a higher C3 titre than the other diet groups when assayed by enzyme immunoassay. Furthermore, opsonophagocytic activity was highest when PEC or SP taken from mice on the 20% case in diet were incubated with radiolabelled microorganisms in the presence of fresh serum taken from the 7% casein group. The production of superoxide anions from PEC and SP was lowest in the mice fed on 5% casein when activity was expressed as nano-mol per animal. It is suggested from these results that the greater activity of phagocytic cells in the presence of increased amounts of C3 and IgM explains the heightened resistance in the mice fed on a 7% casein diet, and that suppressed opsonophagocytic activity resulting from the decreased number of leukocytes in the blood and other phagocytic cells explains the lowest resistance in the 5% casein group. However, mice fed on a 40% casein diet showed all these immunological parameters untouched, and their lowered resistance could not be explained. Different factors seem to be operative in them.

In vivo anti-complementary activities of the cobra venom factors from Naja naja and Naja haje

The kinetics of complement (C) depletion and recovery of C levels upon injection of BALB/c mice with cobra venom factors (CVF), from N. naja (C3- and C5-depleting) and N. haje (selectively C3-depleting) were studied. The animals received i.p. or i.v. injections of either of the two preparations. CH50 and hemolytic C3 and C5 levels were followed as parameters of residual complement activity. N. naja CVF turned out to be as efficient in depleting total complement activity as N. haje CVF. Decreased CH50 values could largely be ascribed to C3 depletion. Complement consumption after N. naja CVF, however, lasted longer than after N. haje CVF administration. Estimated functional half-lives of N. naja and N. haje CVF were 11.5 and 4.5 h, respectively. Inhibition ELISAs showed that, after in vivo administration of either of the two CVF preparations, antigenic C3 and C5 kept circulating for days.

Functional assay of C5-activating and nonactivating cobra venom factor preparations in the mouse system

This paper deals with a new, functional assay of cobra venom factor (CVF) preparations with or without C5-activating property. Existing methods lack sensitivity and use diluted human complement as target of inactivation. An adapted assay using diluted mouse serum as complement source was hampered by underestimation of C3 depletion by bystander lysis and an overvaluation of C5 consumption resulting from C3 inactivation in the reagent used. These disadvantages prompted us to develop the new assay which is based on the incubation of CVF preparations with undiluted mouse serum. After incubation, residual total C activity, as well as functional C3 and C5 are estimated by titration. The procedure permits the assessment of CVF activities with minimal interference from undesired processes. The conditions in the new assay approach the in vivo situation in mice by the use of undiluted serum from the same animal species.

Mouse strains with typical mammalian levels of complement activity

Common laboratory mouse strains have very low complement levels relative to humans, rats, guinea pigs, rabbits and other mammals, which limits the value of the mouse as an experimental model. We therefore tested serum complement levels of 43 mouse strains and 11 rat strains, for the purpose of selecting a convenient laboratory animal having high complement levels. Total complement activity was determined with both erythrocytes and human tumor cells as targets. Eight mouse strains were identified that have complement levels comparable to those of other mammals. These mouse sera lyse tumor cell targets as well as sera from humans, rats or guinea pigs, although they are somewhat less active than rabbit sera. They are relatively inefficient in lysing erythrocyte targets, yet are as active as rabbit serum in this assay. Target cell lysis was demonstrated to be via the classical pathway of complement activation. Of the eight 'high complement' mouse strains, four were recently derived from wild mice, and one, SF/CamEi, was derived from wild mice in 1951. The three other strains, BUB/BnJ, DA/HuSn and RIIIS/J, were developed more than 40 years ago, but apparently were not tested previously for complement activity. Using the BUB mouse as a representative of the 'high complement' mice, we assayed levels of the nine complement components, in an attempt to identify the cause of high complement activity. No difference in levels of C1, C2, C4, C8 or C9 was detected between BUB and BDF1 mice. C2 activity was very low in both strains. C3, C5, C6 and C7 activities were higher in BUB mice than in BDF1 mice, indicating that variation in these complement components is responsible for the difference in total complement activity. The genes determining the 'high complement' phenotype appeared to be semi-dominant in F1 hybrids. The 'high-complement' mouse strains, and recombinant strains derived from them, will be useful in a wide range of biomedical research.

Rapid isolation and characterization of native mouse complement components C3 and C5

A rapid, 1 day procedure for the purification of mouse complement factors C3 and C5 is described. The method is based on fractionated precipitation by polyethylene glycol 6000, followed by Mono Q anion exchange chromatography on a system for fast protein liquid chromatography (FPLC). For C3 isolation, an additional FPLC separation step using Superose 12 (gel filtration) was used. C3 was purified 71-fold with a yield of 32% as measured by biological activity; the preparation contained no detectable contaminants as judged by SDS-PAGE. A comparable procedure for the isolation of C5 resulted in a preparation with a considerable contamination which could be easily removed by affinity chromatography using antibodies directed against these contaminants. With this combined procedure C5 was purified 536-fold with a yield of 28% based on biological activity. SDS-polyacrylamide gel electrophoresis revealed that mouse C3 and C5 had apparent Mrs of 170,000 and 190,000, respectively. Under reducing conditions the alpha and beta chains showed Mrs of 107,000 and 62,000 for C3, and 104,000 and 85,000 for C5.

Tumor necrosis factor/cachectin. Induction of hemorrhagic necrosis in normal tissue requires the fifth component of complement (C5)

TNF induces hemorrhagic necrosis (HN) when injected into skin exposed to bacterial agents but not when injected into normal skin. In this paper, we present several lines of evidence suggesting that TNF requires the fifth component of complement (C5) to induce HN in skin exposed to bacteria. First, mouse strains that do not have C5 did not develop HN after injection of TNF and bacteria into skin. Second, plasma from C5-sufficient mice could correct the defect in these C5-deficient mice. Third, heating at 56 degrees C for 30 min inactivated the capacity of plasma to reconstitute C5-deficient mice. Fourth, CVF, which is known to inactivate complement, abrogated the capability of C5-sufficient mice to respond. Fifth, depleting plasma of hemolytic activity while generating C5a did not affect the capacity of the activated plasma to reconstitute C5-deficient mice. Finally, only the plasma fraction containing molecules of the size range of C5a reconstituted C5-deficient mice. These findings indicate that C5a and not the membrane attack complex is required for HN. Although we do not know through which mechanism C5a participates in the development of HN, we propose that the described HN response is related to a local defense mechanism in which TNF and C5a lead to the disruption of capillaries in the direct vicinity of bacteria. By this mechanism the rapid spread of bacteria or their products into the circulation is prevented. Such a tissue response is consistent with the known higher susceptibility of C5-deficient mice to bacterial infections and provides a model with which to search for the multiple steps involved in this important local defense mechanism.

An improved sensitive and simple microassay of mouse complement

A simple and fast hemolytic microassay was developed for the determination of classical pathway complement activity in mouse serum. The assay is based on hemolysis of sheep red blood cells (SRBC) that are sensitized with polyclonal mouse antibodies. The degree of hemolysis was measured in the reaction supernatants by photometric reading in an ELISA plate scanner at 405 nm wavelength. It was found that some batches of unpurified mouse anti-SRBC antibodies gave insufficient hemolysis. Analysis of two antibody preparations indicated that this might be caused by anti-complementary factors in the ascites fluid, and by an excess of non-complement fixing IgG1 antibodies. For optimal and standardized results, removal of anticomplementary factors and enrichment for complement fixing IgG2 antibodies was required and was achieved using protein A purified anti-SRBC IgG. In our assay it is possible to determine CH50 titers in triplicate in 80 microliters samples of individual mouse sera with high sensitivity. Using this rapid one-step method large numbers of tests could be performed in 1 day.

Neutrophil accumulation and cutaneous responses in experimental cutaneous candidiasis of genetically complement-deficient mice

Mice deficient in the fifth component of complement were studied for their ability to respond to and clear experimental cutaneous Candida albicans infections. The complement-deficient animals took longer to clear the infections and developed a significantly greater delayed hypersensitivity response to Candida than did normal animals. However, although the serum of the complement-deficient animals was incapable of generating in vitro chemotactic activity for neutrophils after appropriate stimulation, the epidermal neutrophilic infiltrate in the Candida-infected skin of these animals was equivalent to that in the normal animals. The progression of the infection, including the early relocation of the invading Candida pseudohyphae to a more superficial site in the stratum corneum and the thickening of the epidermis itself, was also similar in the complement-deficient and normal animals. Therefore, although mice lacking the fifth complement component cannot generate complement-derived serum chemotactic factors and are somewhat less efficient in clearing experimental cutaneous candidiasis, the accumulation of neutrophils in the Candida-infected skin of these animals and their initial cutaneous responses to the infections are normal.

House dust allergen activates the classical complement pathway in mouse serum

A house dust fraction was tested for complement activation in mouse serum using a microtitre complement fixation assay. It was observed that the preparation was a potent activator of the classical, but not of the alternative pathway suggesting an analogy with the complement activation in human serum. The activation showed similarity with that by classical complement activators such as aggregated IgG, DNA, lipopolysaccharide (LPS), but some discrepancy with mite allergen was observed. The contamination of the preparation with LPS was negligible and could not account for the anticomplementary effect. The role of DNA fragments in the activation of mouse complement by the house dust fraction is discussed. Our results suggest that the mouse is suited to study the role of complement activation by house dust constituents in the induction of the IgE response.

Assay of classical and alternative pathway activities of murine complement using antibody-sensitized rabbit erythrocytes

Methods for measurement of classical complement pathway activity (CH50) and alternative complement pathway activity (ACH50) in mouse serum using rabbit erythrocytes sensitized with guinea pig anti-rabbit erythrocyte antibody have been established. The assays measured CH50 values in mouse sera that could hardly be determined by the conventional method using antibody-sensitized sheep red blood cells. Mouse serum ACH50 values determined by the method were also 5-7 times higher than those obtained in conventional assays with rabbit erythrocytes. Both the CH50 and ACH50 values varied with the strain among the 25 different strains of mice studied. BALB/c (nu/nu, male), LT/SuJ and Jcl-ICR27 strains exhibited higher CH50 values, and NIH (nu/+), ICR (nu/nu), NOD (male) and AKR strains showed lower values. The ACH50 was higher in C3H/HeN (male), C57BL/6J (male), Jcl-ICR27 and BALB/c (nu/nu, male) mice, and lower in ICR (nu/nu), NOD (female) and AKR mice. Sera from 16 out of the 25 mouse strains showed ACH50 values comparable to or higher than those in man. As for CH50, however, even the highest value seen in BALB/c (nu/nu, male) mice corresponded to about three-fifths of an average value in man. It is concluded that the complement system of mice, especially the alternative pathway of complement activation, functions as actively as that in man. It was also found that male mice have higher CH50 and ACH50 values than female mice. The differences in these parameters between males and females were only slight at the age of 4 weeks and became conspicuous after 6 weeks at which time both the CH50 and ACH50 virtually reached their respective peak levels of activity.

Study of the optimal reaction conditions for assay of the mouse alternative complement pathway

The optimal reaction conditions for hemolytic assay of alternative complement pathway activity in mouse serum were investigated. A microtiter system was used, in which a number of 7.5 X 10(6) rabbit erythrocytes per test well appeared to be optimal. Rabbit erythrocytes were superior as target cells over erythrocytes from a number of other animal species. The optimal conditions were as follows: an incubation temperature of 39 degrees C, an ionic strength of about 200 mM, and a magnesium concentration of 2.5 mM. Incubation during 60 min was not sufficient for an end-point titration. Addition of 1 mg of zymosan A per test well, however, enhanced and accelerated the hemolytic activity of mouse serum via the alternative pathway resulting in a maximum value after 45 min. This, most probably, proceeded by a mechanism involving the formation of a zymosan-C5-convertase and bystander lysis of the target cells. In contrast to the normal alternative pathway assay the zymosan-potentiated test did, most probably, not involve natural antibodies. Cobra venom factor was more efficient in enhancing the sensitivity of the assay for the mouse alternative complement pathway than zymosan. This makes this factor very useful for testing C-poor body fluids.

Measurement of modulation of mouse complement levels in vivo, utilizing a microtiter hemolytic assay

The complement system, with its protein components, plays a fundamental role in host defense as the major immunological mechanism of innate immunity. Effects of immunotoxic agents on serum complement have not been studied due to the lack of an assay capable of measuring the in vivo effects of compounds in the mouse, the species of choice for immunotoxicological testing. A microtiter hemolytic assay was developed and utilized to measure modulation of serum complement in vivo in B6C3F1 mice. In order to validate this functional assay. Cobra Venom Factor (CVF) was used to produce decomplementation. CVF administered intravenously produced a dose-dependent suppression of complement activity when evaluated 24 hours after a single injection. Administration of 25 or more anticomplementary units (ACU/kg) completely abolished functional hemolytic activity. The duration of the effect was dose dependent with 100 ACU/kg suppressing the response for 48 hours. A decomplemented state could be maintained for up to 6 days, with a second injection. A third injection failed to prolong the decomplementation. Elevated complement levels were obtained following a single injection with Pyran Copolymer. Pyran, a macrophage activator, produce a dose dependent increase in serum complement levels 8 days after administration. The microtiter hemolytic complement assay represents a useful tool capable of evaluating the in vivo effects of agents on serum complement in the mouse.

Complement inhibitory and anticoagulant activities of fractionated heparins

Almost monodisperse heparin fractions (Mw/Mn less than 1.1) were obtained by gel filtration of a commercial heparin. These fractions were assayed for anticoagulant activity (thrombin times and APTT), chromogenic anti-factor Xa activity, inhibitory activity for the human classical complement pathway, carboxyl group content and total sulfate content. Linear relationships were observed between the molecular weight of the heparin fractions and the anti-coagulant activities as determined by thrombin time- and APTT-assay and the classical complement pathway inhibitory activity. On the other hand a hyperbolic-like relationship was observed between the molecular weight of the heparin fractions and the chromogenic anti-factor Xa activity. The heparin fractions did not show significant differences with respect to the carboxyl group and total sulfate content. Low- and high affinity heparin fractions were obtained by affinity chromatography using immobilized AT III. High- and low-affinity fractions greatly differed not only with respect to their APTT activity, but also where their complement-inhibitory activities were concerned. The latter in contrast to literature data available. These differences could not be explained by the observed differences in molecular weight of high and low affinity heparin respectively.

In vivo and in vitro effects of sodium azide on mouse complement

A microtiter hemolytic assay was utilized to determine sodium azide (NaN3) modulation of B6C3F1 and C3H mouse serum complement levels in vivo and in vitro. Functional complement was expressed in CH50 units per milliliter. Experiments were performed to determine the in vitro effect of NaN3 on complement mediated lysis of IgM sensitized rabbit erythrocytes. Concentrations of 5, 10, 20, 30, 40, 60, and 80 mM NaN3 were added to microtiter wells containing Tris buffer, IgM sensitized rabbit erythrocytes, and serum complement from naive female C3H mice. Although NaCl and KCl controls had an inhibitory effect, NaN3 demonstrated a significant dose-dependent inhibition of complement-mediated lysis. In the three in vivo experiments, female B6C3F1 mice were exposed to NaN3 and physiological saline (vehicle control). Complement hemolytic ability was evaluated after a 1-day, single iv injection of 0.2, 2.0, and 20.0 mg/kg NaN3; at Days 1, 2, 3, 4, and 6 of a 6-day time course study after ip administration of 20 mg/kg NaN3; and at the end of an 11-day study involving daily injections of 10, 15, and 20 mg/kg NaN3 given ip. No significant changes in complement-mediated hemolysis were observed in the in vivo experiments. These studies indicate that NaN3 does not affect mouse complement levels in vivo. However, NaN3 suppresses in vitro complement hemolytic ability.

Microassay for colorimetric estimation of complement activity in guinea pig, human and mouse serum

A sensitive colorimetric microassay for determining haemolytic complement activity was devised. It is carried out in U-welled microtitre dishes covered with plastic tape, which are incubated in a waterbath and subsequently centrifuged. The supernatant is transferred to flat-bottomed microtitre dishes and haemolysis is estimated by automatic measuring of the absorption using an interference filter of 405 nm in a Titertek Multiskan. Advantages of the method described are saving time and materials, and avoiding the use of radioactive nuclides. This microassay may therefore be a useful substitute for macro and semi-micro tests for colorimetric determination of serum complement activity and for microassays based on the release of a radio-isotope.

Determination of serum bactericidal activity with the aid of luminous bacteria

Nonmarine luminous bacteria belonging to the genus Vibrio cholerae were extremely sensitive to the bactericidal activity of human serum. Luminous bacteria incubated in a medium containing serum showed a decrease in their in vivo luminescence that was directly proportional to the decrease in the viable count and was a function of the serum concentration. Both immunoglobulins and the complement system were required to exert the serum bactericidal activity. Serum lacking immunoglobulins or certain complement components, especially C3, did not affect the luminescence. The bactericidal effect of the serum on luminous bacteria was diminished by the presence of lipopolysaccharide or by pretreatment of the serum with different species of killed bacteria. As found in other systems, the bacteriolytic activity of serum was only augmented by lysozyme, but was not lysozyme dependent; although the luminous bacteria were converted into spheroplasts in serum containing 0.5 M sucrose, their in vivo luminescence was almost not affected. This system could easily distinguish between the C classical pathway and the properdin pathway. Ethylene glycol-bis (beta-aminoethyl ether)-N,N'-tetraacetic acid, which inhibits only the classical complement pathway, did not inhibit the decrease in luminescence as did EDTA. Thus, it was possible to distinguish between deficiencies in complement components participating in both pathways and complement components that were involved only in the classical pathway. This system could also be used as a substitute to the hemolytic system in complement fixation tests.

A study of the sensitivity of erythrocytes to lysis by heterologous sera via the alternative complement pathway

In order to get insight in the distribution of alternative complement pathway activities as detected by lysis of xenogeneic erythrocytes in the presence of magnesium and ethyleneglycol-bis-(2-aminoethyl)-tetra-acetic acid (EGTA) over the species, the 156 heterologous combinations of erythrocytes and sera out of thirteen animal species were tested. An order could be noticed in the species with respect to serum complement activity tending to negative correlation with the sensitivity of the corresponding erythrocytes to lysis by heterologous sera. So far, the most sensitive erythrocyte for each individual serum must be considered to be the target cell of choice for developing assays for alternative complement pathway activity in the serum involved. In this series of animals only for rabbit serum no sensitive target cell was found. The order observed, in connection with the failing lysis of erythrocytes by homologous sera, suggests further that in restriction of heterologous hemolysis in general one erythrocyte-associated, species-nonspecific regulatory principle may be involved, whereas in homologous restriction, most probably, also species-specific factors play a role.

Antitumour activity of endotoxin, concanavalin A and poly I: C and their ability to elicit tumour necrosis factor, cytostatic factors, and interferon in vivo

Concanavalin A, endotoxin, poly I: C, and tumour necrosis serum (TNS) were compared for antitumour activity against Meth A sarcoma transplanted in syngeneic BALB/c mice and their capacity to induce tumour necrosis factor (TNF), heat-stable cytostatic factors, and heat-labile interferon in the blood of normal and Corynebacterium parvum-pretreated mice. All the agents induced hyperemia and inhibition of mitosis at 4 h, and by 24 h many tumours had a dark necrotic centre. Subsequent tumour growth was inhibited and in some of the treated mice tumours regressed completely. Poly A: U and normal mouse serum did not induce regression and their effects were less marked in all other respects, suggesting that these events may be linked. The necrotizing effects of concanavalin A and poly I: C are unlikely to be mediated by TNF, because neither agent could mimic endotoxin in eliciting RNase-resistant necrotizing and regressing activity in the serum of mice pretreated with C. parvum. Poly I: C did not induce strong cytostatic activity in the sera of C. parvum-treated mice, and for this and other reasons these factors are unlikely to be responsible for the observed effects. Concanavalin A, endotoxin, and poly I: C induced high levels of serum interferon but purified interferon had only weak antitumour activity in the Meth A system, suggesting that interferon may not be the mediator. From these and other data it is concluded that there is no clear relationship between the capacity of the agents to induce tumour necrosis and their capacity to elicit TNF, cytostatic factors, and interferon.

Effects of immunological adjuvants on the mouse complement system. I. The inability of the polyanion heparin to act as an adjuvant is paralleled by inefficient alternative complement pathway inhibition

Interference with hemolytic complement activity by polyanionic substances was studied in relation to the ability of these compounds to act as an adjuvant for a dead listeria vaccine. Heparin appeared a poor inhibitor of the mouse alternative pathway not only in contrast to its effects on the mouse classical and the human classical and alternative pathways, but also when compared to two polyanions with known adjuvant activity: dextran sulfate and suramin. For the three polyanions mentioned a correlation between adjuvant activity and mouse alternative pathway inhibition was observed. These findings suggest a possible causal relationship between interference with alternative complement pathway activation and adjuvant activity.

Spontaneous regression of Friend virus-induced erythroleukemia IX. Role of complement in leukemia regression

The role of complement was examined in the immunologically-mediated spontaneous regression of erythroleukemia induced by the RFV strain of the Friend virus complex. Hemolytic complement levels were not significantly altered during the leukemic, regressed and recurrent phases of the disease. No correlation was observed between leukemia regression and complement levels in normal, C5-deficient and hybrid mice. No correlation was observed between serum complement activity and leukemia recurrence or mortality due to leukemia. The data suggest that hemolytic complement, and thus those immune effector functions specifically dependent on full complement activity, are not involved in leukemia regression and do not influence the course of the disease.

Involvement of membrane-associated sialic acid in the resistance of sheep erythrocytes to lysis by mouse complement

The sensitivity of the murine complement system to regulation by membrane-associated sialic acid was investigated. Therefore the C-mediated lysis of sialic acid-rich sheep erythrocytes, sialic acid-poor rabbit erythrocytes and enzymatically desialylated sheep erythrocytes was studied. Mouse complement differed from human and guinea pig complement in that besides the alternative, also the classical pathway appeared sensitive to regulation by surface sialic acid. The possible reaction mechanisms behind the selective sensitivity of the murine classical pathway to membrane-linked sialic acid are discussed and will be subject of further study.

Interactions of killed Listeria monocytogenes with the mouse complement system

Incubation of mouse serum with Listeria monocytogenes involved activation of the alternative complement pathway, resulting in depletion of both classical and alternative pathway activity. The activation process gave rise to reactive (calcium- and magnesium-independent) lysis of, specifically, rabbit erythrocytes, which become resistant to this form of hemolysis by sensitization with antibodies. The possible implications of these findings for L. monocytogenes as an intracellular parasite and for rabbit erythrocytes as target cells for mouse alternative complement pathway activity are discussed.